Technical Guidelines

Book Content

Part I Architectural Guidelines ........................................................................................................................... 1 1

2

3

4

5

Introduction ........................................................................................................................................... 1 1.1

Eco-efficacy of the building envelope ............................................................................................... 1

1.2

Objectives of the SWIFT (Switchable Façade Technology) Project................................................. 4

1.3

References ....................................................................................................................................... 6

1.4

Iconography ...................................................................................................................................... 6

A SWIFT Change in the Historical Evolution of Glazing ....................................................................... 7 2.1

Brief history of glass and glazing...................................................................................................... 7

2.2

Chromogenic Glazing: Electrochromic and Gasochromic devices ................................................ 17

2.3

From passive to dynamic devices: environmental and aesthetic concerns ................................... 20

2.4

The Integration of Switchable Glazing in Daylight Design.............................................................. 25

2.5

References ..................................................................................................................................... 32

2.6

Iconography .................................................................................................................................... 32

Guidelines for architects and end-users ............................................................................................. 33 3.1

The need for switchable façades.................................................................................................... 33

3.2

Application criteria: control strategies and design considerations.................................................. 37

3.3

Architectural Potential of Switchable Glazing ................................................................................. 49

3.4

A “chameleon” skin for a sustainable architectural envelope ......................................................... 53

3.5

References ..................................................................................................................................... 55

3.6

Iconography .................................................................................................................................... 56

Description of the case studies ........................................................................................................... 57 4.1

Practical integration of an Electrochromic façade at TU Eindhoven .............................................. 57

4.2

Practical integration of an Electrochromic façade at office room in Rome..................................... 62

4.3

Practical integration of switchable glazing in offices in Freiburg .................................................... 65

4.4

References ..................................................................................................................................... 72

4.5

Iconography .................................................................................................................................... 72

Building integration and simulation results ......................................................................................... 73 5.1

The reference office........................................................................................................................ 73

5.2

Simulation tools and methodology.................................................................................................. 73

5.3

Daylighting and artificial lighting ..................................................................................................... 74

5.4

Optimisation of the control strategy ................................................................................................ 75

5.5

Energy savings ............................................................................................................................... 76

5.6

Peak load reductions ...................................................................................................................... 77

5.7

References ..................................................................................................................................... 77

5.8

Iconography .................................................................................................................................... 78

Part II: Technical Guidelines ............................................................................................................................ 79 1

Introduction ......................................................................................................................................... 79

2

Gasochromic and electrochromic system components ...................................................................... 79

3

4

5

6

2.1

Gasochromic system and its components...................................................................................... 79

2.2

Electrochromic system and its components ................................................................................... 81

Profile systems for windows and facades ........................................................................................... 84 3.1

Window designs.............................................................................................................................. 84

3.2

Facade designs .............................................................................................................................. 86

Prototype data..................................................................................................................................... 88 4.1

Gasochromic glazing ...................................................................................................................... 88

4.2

Electrochromic glazing.................................................................................................................... 89

4.3

Prototype frames ............................................................................................................................ 89

Planning a project ............................................................................................................................... 90 5.1

Requirements for switchable facade frame profiles (both systems)............................................... 91

5.2

Project-specific requirements ......................................................................................................... 93

Mounting instructions .......................................................................................................................... 95 6.1

General glazing guidelines ............................................................................................................. 96

6.2

Special instructions for working with switchable glazing ................................................................ 96

7

Documentation of a project ................................................................................................................. 97

8

Literature ............................................................................................................................................. 99

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Architectural and Technical Guidelines

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Part I Architectural Guidelines 1 Introduction 1.1

Eco-efficacy of the building envelope

Man can be considered as a living being that, placed in a defined environment, maintains with it a series of relationships that are necessary to know and to control so as to optimise any architectural project. These relationships are, basically, energetic exchanges of different type determined, in general, by the fact that the human body tends to keep stable his own conditions (homeostasis) as regard to a surrounding environment that changes dynamically, eventually modifying its characteristics through intelligent techniques and complementary systems 1 (energetic resources, defensive barriers, etc.) . In other words, we may say that, since the environment seldom supplies to the human body the proper mixture needed in every single moment, man has settled some “improving devices” that may act as “interfaces” between the inner micro-environment of the body and the external macroenvironment of Nature, in order to modulate the interaction of environmental stimuli and to create a system of interchanges, whose characteristics may be adjusted, on request, on the basis of particular exigencies. Obviously, amongst them, there is Architecture (Fig. 1.1.1).

1.1.1 The Villa Adriana in Tivoli

Being aware of the basic relationship between built structures and environment (1.1.2), it is worth noting that in the current debate - albeit recently - people have started to talk of the building envelope as a “skin” and not only as a “protection” from external agents, something that “breathes”, that modulates, in the wider sense of the word, climatic and environmental conditions between inside and outside, as if talking of a living organism. For this reason, the definition of the edifice as a “built organism” is really significant, since, just as a living being, its prevailing element results in the exchange of matter and energy with the context; moreover, when something out of normality happens, the living creature may react, mistakes can be corrected, functions can be revised. It is interesting, therefore, to try to incorporate analogues considerations even in the current process of architectural design and scientific research, so as to develop buildings with complex, variable and adjustable relationships between inside and outside, and with adaptable qualities from the thermal and visual point of view. On the other hand, we do live in a world that is dynamic and constantly evolving: a living organism much like our own bodies. The places where we live, the work we perform, even our institutional references (religious, cultural, political, etc.) change and vary from day to day, so it is fundamental for us, and for the built environments that surround us, to take 2 part, or at least be aware, of these changes . In this sense, thinking of the building envelope as a “membrane”, or as the 1.1.2 Archaic temples in Delphi, Greece “skin” of the built organism, implies, on the one hand, a confirmation of the osmotic quality of an exchange process that concerns fluxes of energy and information, just like a cell (1.1.3); and on the other, it implies anticipating the increasingly predominant role that the constructive solution of this component has conquered within the expressive and technological experimentation. In fact, by adopting the concept of skin to illustrate the meaning of the architectural envelope in the overall functioning of the built organism, we intend to explicitly emphasise the sensible and, somehow, living nature of a part of the building that is appointed to mediate the relationship between man and the environment; hence, an element that, being initially mainly a Contract ENK6-CT1999-SWIFT

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static protective barrier, has gradually specialised in a complex selective and polyvalent structure, a dynamic filter able to promptly react to the solicitations coming from the context, and even able to show the beating of life inside the buildings. Obviously, such an outcome should derive from a dialectic exchange with the natural and environmental aspects characterising a given site, thus revealing, to the building envelope, a sensitiveness comparable to the one expressed, in other ways, in biological sciences. As a matter of fact, it is undoubtedly significant the fact that the technological research is trying to find the inspiration and the analogies useful to define the roles and the performances that a “sustainable” building envelope should meet, driving a parallel with the biological, vegetal and animal world. It is already well established, actually, that just the Nature has developed during its evolution an incredible multiplicity of strategies aimed at saving energy, matter and information, at their rational use, and, in general, at the optimisation of metabolic exchanges, both in material and immaterial terms (1.1.4).

1.1.3 Structure of a cell

Indeed, the attempt to imitate some aspects of the biological world has recently given rise to a new discipline within the science of materials. In this research context, the greatest aspiration seems to be the capability of realising components able to perform as a projected version of the human skin, where the sensitivity and adaptability acquired by the device may make it react to changing external factors, or, anyway, contribute to modify its initial status in favour of a specific required performance. Science and technology have had as a fundamental stimulus the idea of realising materials able to perform in an “intelligent” way, i.e. self-modifying and self-controlling; actually, a surface that modulates its coloration, according with the fluctuation of external stimuli, is a clear example of a transformism comparable to the dynamic reaction of a “sensible” and “intelligent” skin, that, in relation with the surrounding environmental conditions, reacts basing on his planned capability to change. Within the building industry, on the other hand, the need for the integration of reactive and adaptive techniques is also strictly dependent on the disadvantages, already widely known, of passive systems (1.1.5), that allow a constant and univocal reactivity set on intermediate values, and respond only partly to extreme situations. Those considerations gave the chance to accelerate the research on more efficient and dynamic systems, able to provide differentiated performances and to adapt both to the variability of external changes and to varied exigencies of users.

1.1.4 Examples of natural evolution

A major interest, obviously, has been concentrated on the transparent component of the envelope, considered to be its weakest part, easily penetrable, and thus difficult to manage for the control of passing solar radiation and heat. The transparency of the glazed envelope gives the chance to erase the boundaries between the interior of a building and the outside world; this could be desirable aesthetically, but may imply major climatic drawbacks, both for illumination and thermal concerns. In winter, for example, the advantage performed by glass façades represents a huge potential for energy gain from the solar radiation; those heat gains can even compensate, for a large part, the heat losses. In summer, however, such solar gains are less desirable and they can have to be reduced through appropriate control measures. Here comes the definition of switchable dynamic transparent materials, i.e. materials endowed with the capacity to modulate their degree of light and energy transmittance, transparency, translucency and even colour, in a reversible way, so as to shield the incoming solar radiation, eventually up to its total preclusion. If applied on a transparent support, they can give it Contract ENK6-CT1999-SWIFT

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the possibility to control the luminous and energetic flux for a predetermined period of time, then coming back to the initial state and repeating the same operation several times. Whether those devices will gain wider application has yet to be determined; however, the concept of those dynamic systems is to allow designers a greater flexibility in responding to changing programmatic requirements, and to obtain visual and thermal comfort.

1.1.5 Nouvel; Fondation Cartier, Paris


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1.2

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Objectives of the SWIFT (Switchable Façade Technology) Project

As a result of intensive R&D (Research and Development), a new class of glazing, which can allow for changing the transmittance of the windows by coating technology (Electrochromic, EC, and Gasochromic, GC), is on the way to enter the market. The integration of those “switchable” devices in the building transparent envelope may provide a reliable, clean, efficient and safe building cladding, incorporating the functions of high-performance windows, efficient solar shading and daylight provision. Thus, switchable façade technology can represent a big step towards a more sustainable building envelope, important for the promotion of modern concepts of building architecture, in which daylight becomes a fundamental factor, introducing transparency in inhabited spaces, while increasing living comfort and working conditions for the occupants. The energy consumption is reduced by an optimum balance between daylight provision and solar shading; the primary energy demand for heating, cooling and lighting shall be consequently minimised.

1.2.1 The SWIFT Logo

Nevertheless, a lot of technical, engineering, architectural and general public interest questions are yet to be answered, and the SWIFT (Switchable Façade Technology) Project, funded by the European Commission within the Framework FP5, has been set up to give a contribution in this direction (1.2.1). Actually, for the realisation of switchable façades, the state of the art is different for the two main options, i.e. Electrochromic and Gasochromic devices; anyway, for both 3 technologies there is a need for research and innovative work . Within three years duration, this interdisciplinary industry related project has been aimed at leading the switchable façade technology to the market, developing a relevant, reliable, user-oriented and comprehensive knowledge basis. Within four major work packages, the SWIFT project has answered important questions in the areas of Characterisation, Reliability, Building Integration, and Sustainability (Environmental and Economic Impact), paving the way towards a broad implementation of switchable technologies, giving insights into their benefits and limits, and providing guaranteed and objective guidance and performance information to end users (1.2.2).

1.2.2 Switchable façade simulations

These tasks have been performed through the following work items: - Realistic and comprehensive characterisation of switchable glazing façades in the areas of thermal, visual, solar and shading performance; - Assessment of allowable load limits in magnitude and time duration for a reliable performance of the complete façade system; - Investigation and evaluation of possible failure modes with a defined methodology (FMEA); - Definition and integration of complete working system components; - Development of control strategies for switchable façades and artificial lighting/HVAC; - Investigation of performance and acceptance by the end-user in a real environment; - Investigation of European market, energy savings and CO2-reductions; - Adapted life-cycle-analysis of switchable façades with respect to indicators of energy and CO2-emissions; - Investigation of end-user comfort parameters. In particular, the first work package, Characterisation, has focused its attention on the full characterisation of the materials in the lab, so as to develop building components models that describe the performance of the Contract ENK6-CT1999-SWIFT

1.2.3 Laboratory measurements

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switchable façade in sufficient detail (1.2.3). Switching conditions and reactions to meteorological changes have been characterised realistically, while outdoor testing provided dynamical data of real installations to be used as validation basis under real environmental conditions. Comparing test cell monitoring with simulated results has permitted the analysis of 3 discrepancies so as to identify possible errors or simplifications . The work package on Reliability has investigated the durability and reliability of the technologies; it included outdoor and indoor testing as well as a failure risk analysis. The conditions for minimised failure risks have been identified (FMEA, Failure Mode Effect Analysis) and have been applied to all functional parts of the complete façade (glazing, control unit, electrical connections, etc.). The experimental tests have investigated conditions for the reliable use of switchable glazing through continuous cycling under outdoor exposure, while several accelerated indoor tests have been performed included 3 modified version of standard test procedure (1.2.4).

1.2.4 SWIFT test box in Grenoble

In Building Integration, pilot test façades have been designed and built in Eindhoven (TU/e), Rome (ENEA) and Freiburg (ISE) in combination with adapted lighting and suitable control systems (1.2.5). Monitoring and evaluation of user acceptance, by questionnaires and assessment studies, have given detailed information on the performance of the technologies, while the use of the façade models in simulation tools has permitted the integration and the modelling of switchable façades in lighting and energy building simulations. A representative “reference office”, with defined variations exemplifying a large number of cases in reality, has been designed and described to compare simulations. In addition, since switchable façade technology saves energy and reduce CO2 considerably only if façade, artificial lighting and HVAC installations work together co-operatively, the activities have been focused on the optimisation of the interaction between these three components. Putting all information and expertise together has permitted the development of guidelines for designers, end-users and builders, drawing also on results 3 from other work packages .

1.2.5 SWIFT EC test room at TU/e

Finally, in Sustainability, data have been collected, extended and produced, supporting the knowledge on the impact of SWIFT technologies on the environment. Specific advantages and disadvantages have been checked in a marketing study and investigation of possible application area, while climatic variations have been estimated so as to establish a market potential from the information obtained. Environmental impact has been analysed with respect to a selected set of indicators (energy, CO2) rather than a complete LCA, Life Cycle Analysis (1.2.6). Similarly, detailed simulation results of selected cases illustrated the potential reductions of installed peak power and cooling energy load 3 compared to conventional façade options . Summarising, hence, amongst the SWIFT project a comprehensive sound scientific and commercial basis for the implementation of switchable façade technologies in Europe has been developed. It is believed that those investigations could contribute very much to the aim of improving the quality of life, health and employment especially through more reliable planning and improved realisation of better comfort in inhabited spaces. The geographical spread of participants has, moreover, allowed treating the related aspects of daylighting and solar control under different climatic conditions. Probably, awareness of these factors will lead architectonic objects of the near future to be designed in new and innovative ways. It will be important to achieve a balance between the way they fit into the urban plan, their Contract ENK6-CT1999-SWIFT

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architectural form, their relationship with the environment, their typology and their technology. This will naturally also lead to an increasing complexity of the design task, which only could be tackled with any degree of success by means of an “holistic” approach to planning, based on advanced integrated energy concepts and interdisciplinary co-operation between the architects, façade planners and consulting engineers. Since the complexity of the façades relates to an increased demand for high quality services, it is believed that façade designer engineers and other planning profession will benefit from the results disseminated in the project, so as to develop the required skills and knowledge basis to provide optimised building envelopes in combination with adapted lighting 3 and heating control .

1.2.6 LCA Principles

1.3

References

1.

Serra Florensa R., Clima, Lugar y Architectura, IMEAT, Madrid, 1989.

2.

Guzowski M., Daylighting for sustainable design, Mc Graw-Hill, 2000.

3.

Commission for the European Communities, Switchable Façade Technology - SWIFT Project, Proposal description, June 2000.

1.4

Iconography

All the pictures and drawings included in the text are made by the author, except:

- Images n° 1.1.3, 1.2.6 are courtesy of José Flémal (UCL). - Images n° 1.1.4a, 1.1.4b, are taken from the Gimp-Savvy Copyright-Free Web Site: http://www.gimpsavvy.com/PHOTO-ARCHIVE/. - Image n° 1.2.1 is taken from the Project SWIFT Public Web Site: http://www.eu-swift.de. - Image n° 1.2.2 is courtesy of Laurens Zonneveldt (TNO-TU/e). - Images n° 1.2.3 is taken from the Project SWIFT Documentation Report: Commission for the European Communities, Switchable Façade Technology - SWIFT Project, Midterm Assessment Report, October 2001, swift-coord-mtr-011031midterm report.pdf. - Images n° 1.2.4 is taken from the Project SWIFT Documentation Report: Wilson H.R., Heck M., “Results of Visual Inspection”, in WP2- SWIFT Project, 2002, swift-wp2-ip-020626-visual_inspection_results_v3.pdf.


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2 A SWIFT Change in the Historical Evolution of Glazing 2.1

Brief history of glass and glazing

The mysterious physical, optical and aesthetic properties of glass have st always intrigued man (2.1.1). Even the most sophisticated 21 century person is amazed and bemused by this solid, rigid, uncrystallised, “supercooled” liquid ant its treatments (2.1.2). The product and the process used to manufacture it seem to smack of alchemy, for glass is nothing but coarse sand and soda ash transformed into smooth transparent forms. Actually, natural glass has existed since the beginnings of time, formed when certain types of rock melted as a result of high-temperature phenomena such as volcanic eruptions, lightning strikes or the impact of meteorites, and then cooled and solidified rapidly. Stone-age man is believed to have used cutting tools made of obsidian (a natural glass of volcanic origin also known as hyalopsite, Iceland agate, or mountain mahogany) and tektites (naturally-formed glass).

2.1.1 A modern curtain wall

According to the ancient Roman historian Pliny, who wrote his Naturalis Historia in 77 AD, Phoenician merchants transporting stone actually discovered glass (or rather became accidentally aware of its existence) in the Syria region, around 5000 BC. Pliny tells how the merchants, after landing, rested cooking pots on blocks of nitrate placed by their fire; with the intense heat of the flames, the blocks eventually melted and mixed with the sand of the beach to form an opaque liquid. Pliny’s anecdote now is considered apocryptical, but it contains an accurate recipe for producing glass: heat plus silica and soda ash. Anyway, it took two thousand years after its discovery for the idea to emerge that glass was a material that could be used for windows rather than simply for vessels or pots. This may have been because the climate of the place of its “invention” did not require man to create sealed transparent enclosures, and also perhaps because making flat glass was not easy. However, once this imaginative leap had been made, new conceptual languages in architecture became possible, which are still 4 being developed and explored .

2.1.2 H&DeM; SUVA Building, Basel

The earliest man-made glass objects, however, mainly non-transparent glass beads, are thought to date back to around 3500 BC, with finds in Egypt and Eastern Mesopotamia. In the third millennium BC, in central Mesopotamia, the basic raw material of glass was being used principally to produce glazes on pots and vases. It was then, above all, Phoenician merchants and sailors who spread this new art along the coasts of the Mediterranean. The oldest fragments of glass vases, on the other hand, date back to the th 16 century BC, and were found in Mesopotamia. Hollow glass production was also evolving around this time in Egypt, and there is evidence of other ancient glassmaking activities emerging independently around Mycenae (Greece), China and North Tyrol. After 1500 BC, Egyptian craftsmen are known to have begun developing a method for producing glass pots by dipping a core mould of compacted sand into molten glass and then turning the mould so that molten glass adhered to it. While still soft, the glass-covered mould could then be rolled on a slab of stone in order to smooth or decorate it. The earliest examples of Egyptian glassware are three vases bearing the name of the Pharaoh Thoutmosis III (1504-1450 BC), who brought glassmakers to Egypt as prisoners following a successful military campaign in Asia. th

There is little evidence of further evolution until the 9 century BC, when glassmaking revived in Mesopotamia. Over the following 500 years, glass production centred on Alexandria, from where it is thought to have spread Contract ENK6-CT1999-SWIFT

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to Italy; history tells us it was just Alexander the Great who founded the famous glass works after he founded the city itself in 332 BC. The first glassmaking “guidelines”, on the other hand, date back to around 650 BC, since instructions on how to make glass are contained in tablets from the library of the Assyrian king Ashurbanipal. A major breakthrough in glassmaking was the discovery of glass bowling, sometime between 27 BC and 14 AD, generally attributed to Syrian craftsmen from the Sidon-Babylon area. The long thin metal tube used in the blowing process has changed very little since then. In the last century BC, the ancient Romans began blowing glass inside moulds, increasing the variety of shapes possible for hollow glass items. The Romans also did much to spread glassmaking technology. With its conquests, trade relations, road building and effective political and economical administration, the Roman Empire created the conditions for the flourishing of glassworks across the Mediterranean and eastern Europe. During the reign of the emperor Augustus, glass objects began to appear throughout Italy, in France, Germany and Switzerland. Roman glass has been found as far a field as China, shipped along the silk routes. It was the Romans who began to use glass for architectural purposes, with the discovery of clear glass (through the introduction of manganese oxide) in Alexandria around 100 AD. Cast glass windows, certainly up to about one square meter - albeit with poor optical qualities - began to appear in the most important buildings in Rome and the most luxurious villas of Herculaneum and Pompeii. Glass, however, did not totally replace shutters at the windows of Roman homes; actually, probably they did not discover the art of grinding and polishing cast flat glass to make it transparent. Instead of glass, the rich generally used thin, transparent sheets of alabaster to enclose wall openings.

2.1.3 The Parthenon in Athens

2.1.4 The Villa Adriana in Tivoli

However, the nature of the climate was not providing the functional imperative for the fully introduction of the glazed window. In fact, if we look at Vitruvius famous Ten books on Architecture, glass is completely absent; for all his careful analysis of the relationship between the function of buildings and their design, Vitruvius restricts his comments on comfort and climate to recommendations for room placement and orientation. On the other hand, a study of Vitruvius, or of Greek and Roman buildings still standing, shows how the nature of the architecture was comparatively independent of the glazed window concept (2.1.3). There is so much light and heat outside for most of the year that the building interior is seen as a retreat (2.1.4). Of course, window openings formed part of the architectural syntax, but light is often designed to penetrate constructions through columns or holes in the roof (2.1.5). The centuries after Vitruvius saw the gradual development of the idea of glass being an important material in windows, and not merely act as a transparent weather shield; the coloured glass used as an illuminated painted surface, found in Constantine’s Church of St. Paul in Rome, dated 337 AD, is one of those exempla. With the geographical division of the empires, glass craftsmen began to migrate less, and eastern and western glassware gradually acquired more distinct characteristics. Alexandria remained the most important glassmaking area in the East, producing luxury glass items mainly for export. In Rome’s western empire, on the other hand, the city of Köln in the Rhineland developed as the hub of the glassmaking industry, manned, however, by mainly eastern craftsmen. On the other hand, it was in Germany that the Latin term glesum (a Germanic word meaning 4 transparent/luminous) was in use, giving us the name we now utilize .

2.1.5 The Pantheon in Rome

The decline of the Roman Empire and culture slowed progress in the field th


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th

of glassmaking techniques, particularly through the 5 century. Middle Eastern craftsmen dominated the craft until German invader broke their monopoly around 600 AD. Towards the year 1000, a significant change in European glassmaking techniques took place. Given the difficulties in importing raw materials, soda glass was gradually replaced by glass made using the potash obtained from the burning of trees. At this point, glass made north of the Alps began to differ from glass made in the Mediterranean area, with Italy, for example, sticking to soda ash as its dominant raw material. th

The 11 century saw the development in Germany of a technique for the th production of glass sheets, described in the 12 century by the German monk Theophilus as the Cylinder method. By blowing a hollow glass sphere and swinging it vertically, gravity pulled the glass into a cylindrical “pod” measuring as much as 3 metres long, with a width of up to 45 cm. While still hot, the ends of the pod were cut off and the resulting cylinder reheated, cut down in length, flattened out, and smoothed (2.1.6).

2.1.6 The Cylinder method

On the other hand, another type of sheet glass, Crown glass (also known as the “spinning method”), started to be relatively common across western Europe. With this technique, a glass glob was blown, the crown of which (opposite the blowhole) was then removed from the bowling iron, stuck on the punty and spun. Spinning the semi-molten ball then caused it to flatten and increase in size, but only up to a limited diameter of about 600-700 mm. The panes thus created were then joined with lead strips and pieced together to create windows (2.1.7). Those two methods were generating intrinsically different products. In fact, while the cylinder method made larger, comparatively even sheets in terms of thickness, but with surfaces damaged by the necessary reheating and 2.1.7 The Crown Glass spinning method physical flattening, the spun glass was more brilliant, with its untouched finish, but with many air bubbles, concentric rings and uneven lens forms in the centre. However, as they were made in gradually increasing sizes, and as the techniques to cast and then fix them to buildings were consolidated and perfected, they permitted the glories of the Gothic Ages and were still to be used for the next 800 years (2.1.8). Nevertheless, the creation of glass walls characterising the evolution of northern architecture was not only the direct consequence of the technical advances in the formation of glass panes, but also partly a result of climate. The large openings suggested by the idea of “frame” implicit in Gothic Architecture would, actually, have been impossible without the creation of a membrane to keep the northern regions’ weather out, with its long winters and often overcast skies. Moreover, the need for protection from the cold and the rain went together with an increasing appreciation of light (regardless of transparency) and colour (with the development of stained glass), that gradually replaced the instincts for mystery and darkness characterising the previous ages (2.1.9).

2.1.8 The St. Chapelle in Paris

Glazing remained, however, a great luxury up to the late Middle Ages, with royal palaces and churches the most likely buildings to have glass windows; the brilliant bits of coloured glasses with their complex designs were, in fact, probably prohibitively expensive, so even the rich still often shuttered their apertures, and the Middle English word for windows – “wind eyes”- underlines the fact that wall openings enclosed in glass were, for all 5 practical purposes, substantially non-existent . While the northern Europeans were creating their architecture of glass in the great age of Gothic, the city of Venice was enhancing the product to new levels of quality. The Venetian merchant fleet ruled the Mediterranean waves and helped supply Venice’s glass craftsmen with the technical know-how of their counterparts in Syria, and with the artistic influence of Islam. The Venetians were originally renowned for decorative glassware Contract ENK6-CT1999-SWIFT

2.1.9 The Cathedral of Chartres th

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and glass vessels, but they soon expanded their expertise into window glass and lenses for spectacles. A 1271 ordinance laid down certain protectionist measures such as a ban on imports of foreign glass and a ban on foreign glassmakers who wished to work in Venice. th

Until the end of the 13 century, most glassmaking in Venice took place in the city itself. However, the frequent fires caused by the furnaces led the city authorities, in 1291, to order the transfer of glassmaking to the island of Murano, also making it easier for the city to keep an eye on one of its main assets and ensuring that no skills or secrets were exported. The arrival of Italian Renaissance architectural thinking (2.1.10) in northern Europe wrought a radical and irreversible change in building morphology. Glazed enclosures started to lose their powerful impact and conceptual driving force towards the consideration of the material as part of a broad syntax, in which the quality of manufacture became more important than the part it played in building elevations (2.1.11).

2.1.10 The Palazzo Farnese in Rome

Anyway, this drive for quality, together with the comparatively free trade in products and skilled craftsmen, with the subsequent sophistication of the th th market, produced responses in the glass-makers, and the 16 and 17 centuries saw new efforts in the industry to make a better product. Important glassmaking industries developed throughout Europe, and in 1688, in France, a new process was developed for the production of plate glass, principally for use in mirrors, whose optical qualities had, until then, left much to be desired. Actually, the high polish on spun crown was still coming with a limit on size, while the larger sheets available in blown cylinder were characterised by an uneven thickness and flatness, and a dull, sometimes marked, finish.

2.1.11 Detail of Palazzo Farnese

The new technique, the first real innovation in glass making for many centuries, completely revolutionised the skills needed to make glass. A large pouring pot was heated in the furnace and the molten glass poured into it. The pot was then moved mechanically to a casting table, originally made of masonry with a copper top, and poured into a mould, specifically made using iron bars. The treacly mass was then rolled by means of a copper or iron cylinder and, once set, taken to an annealing oven where it stayed for several days before cooling. However, the contact with the copper table surface and the roller still required the complicated part of the process: grinding and polishing. The necessitated grinding was made by spinning a wheel above the plate and pouring water and gradually finer abrasive sand into the interface, while polishing was then carried out using hydrated ferric oxide powder. When polishing was finished, the glass was turned over and the reverse side treated in the same way. The process was very long and expensive, because of the skills needed to avoid breaking the glass or damaging its surface, but the result of this “Plate 4 Pouring” was flat glass with good optical transmission qualities . th

The 18 century saw the new and improved materials assume a natural place in the architecture of the time, with great oscillations in terms of popularity of use between crown cylinder and plate glass. Glazing and fenestration became part of the overall assembly of the external wall, expressed as a hole in it rather then as a membrane filling the space between structural members. More significantly, perhaps, in technical terms, the window had not only to be of a sufficient size for luminous and visual needs, but it had also to be opened. In this sense, the invention of the vertically sliding sash window overcame the problems of weight and hinging typical of previous side-hung systems, permitting, in northern climates, the opening for ventilation without the risk of letting the rain inside. In France, at the same time, croisé windows, composed of a pair of inward-opening glazed doors with a fixed or movable light above and a pair of louvered shutters, solved the problem of opening in hot weather, Contract ENK6-CT1999-SWIFT

2.1.12 The railway station in Milan

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while providing the control of glare and of solar penetration. It was, however, not until the mature stages of the Industrial Revolution that mechanical technology for mass production and in-depth scientific research into the relationship between glass composition and its physical qualities began to appear in the industry. All the same, while glass was being perfected and subordinated to form part of the overall architectural design, it was being put to another use in northern Europe, an use which was to transform architectural glazing and 4 our attitude to it: the development of the conservatory . th

During the early 18 century, the creation of large glass buildings for plants started to become a celebratory experience with a clear social significance; a wonderful mixture of gradually formulated science and design intuition. The principal elements of a passive solar energy system were in place since the beginning: massive masonry, high thermal capacity back wall containing heating flues, and sloping glass walls on the south side. The glazing was often openable to enable plants to be taken out, and to provide ventilation at times of potential overheating; crude “double glazing” consisted of an inner frame incorporating oilpaper. th

The first half of the 19 century saw the flowering of this building type, both as an architectural creation of great beauty, and as a form of significance for the future, laying the formal and technical foundations for a new generation of large covered daylit spaces, which the new industry and commerce was to demand as the century developed into the railway age (2.1.12). It was the emergence of iron as a structural material for use in building and the general diffusion of industrialisation that had a great impact on all uses of glass, creating expertise that resulted in the production of milestones in the history of architecture as the 1845 Palm House at Kew, or the 1851 John Paxton’s famous Crystal Palace.

2.1.13 The Galleria Vittorio Emanuele

The former is, to this day, one of the most beautiful experiences to be had in the world of glass architecture with its smooth curved glazing; a result of scale, simple form and fine and appropriate detailing. The Crystal Palace, on the other hand, and the exhibition that it housed, was a great midcentury manifestation of the British industrial pre-eminence. Its history is one of the best known, and most often told, in western architecture, as one of the world’s first “modern” buildings. With its 80.000 square meters covered by patent plate glazing, its innovative construction methods and its morphology, the Crystal Palace staked out new architectural territories, setting precedents for many of the overlaying characteristics of the new architecture to come in the subsequent fifty years and beyond. th

In short, by the middle of the 19 century, cast-iron columns and wroughtiron rails, used in conjunction with modular glazing, had become the standard technique for the rapid prefabrication and erection of the new large warehouses, market buildings and railway stations needed for urban distribution. The commercial and technical products of the industrial revolution generated a need for building forms that did not exist in the conventional architecture of the time. The creation of extensive railways systems with their termini, the requirement for large distribution market halls, the idea of the glazed shopping arcade, the covered internal street - as Galérie d’Orléans in Paris, 1829, or Galleria Vittorio Emaneule in Milan, 1867 (2.1.13) - were producing a new “brief” for architecture, with the need for very large volumes, often lofty and basically totally daylit. The new glazed roof structures accomplished those new wishes. Historically parallel to the development of these glazed halls, with their Contract ENK6-CT1999-SWIFT

2.1.14 High-rise American buildings

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wonderful transparent walls and roofs, function and commerce drove the formulation for interior spaces interrupted only by columns, thus revealing the façade as a framed opening. In the iron structural frame with a glass wall were laying the seeds of the curtain wall and the building skin that were to be developed a hundred years later. However, the real birthplace for the new iron- or steel-framed architecture has to be found in America (2.1.14), and particularly in the city of Chicago, where a devastating fire had destroyed in 1871 large parts of the downtown area. With the new palette of materials, and the newly invented “elevator”, the architects of Chicago used the resulting urban tabula rasa as a historically unique opportunity for an unprecedented series of buildings exploiting the possibilities of the frame, in which the glazing gradually occupied a larger and larger proportion of the façade.

2.1.15 The Forcault/Pittsburgh method

By the end of the century, buildings such as Adler and Sullivan’s Chicago Stock Exchange, dated 1894, or the Carson Scott Store by Louis Sullivan, built between 1899 and 1904, were turning the corner for architecture into th the 20 century. The new development of the large-scale all-glass envelope as an element th of architecture, whether for walls or roof, in the second half of the 19 century was, nevertheless, accompanied by little real improvement in the manufactured product. Until the turn of the century glass was still available only in the three basic forms: blown sheet or plate, spun “crown” and polished castplate. But striking improvements were at the horizon. A key figure and one of the forefathers of modern glass research was the German scientist Otto Schott, who used scientific methods to study the effects of numerous chemical elements on the optical and thermal properties of glass. Moreover, Friedrich Siemens gave another major contribution in the evolution towards mass production with the invention of the tank furnace, which rapidly replaced the old pot furnace and allowed the continuous production of far greater quantities of molten glass.

2.1.16 The Libbey-Owens method

The new century saw one least effort to improve broad cylinder glass with the introduction of machine blowing, using John Lubbers’ invention of 1896. However, in the production of flat glass the first real innovation came in 1904, when a Belgian named Fourcault managed to vertically draw a continuous sheet of glass of a consistent width from the tank. The molten glass was then drawn up from a slot in the so-called “debiteuse”, itself pushed down slightly into the melt by a series of rollers; size ceased to be a problem, as did the hammered surface of blown plate. The Pittsburgh Plate Company then further developed this process retaining the vertical draw of the Forcault principle, and thus producing sheet glass with a much better surface. (2.1.15). One year later, in America, Colburn developed another method for drawing sheet glass with a process that used knurled rollers rather than a debiteuse, and that turned the glass horizontally after the initial drawing. This process was subsequently further improved with the support of the US firm Libbey-Owens (2.1.16). Around the end of first World War, another Belgian engineer, Emil Bicheroux, developed a process whereby the molten glass was produced by squeezing it from the pot directly through two rollers. Like the Fourcault method, this resulted in glass with a more even thickness, and made grinding and polishing easier and more economical. An off-shot of evolution in flat glass production was the strengthening of glass by means of heat-treatment and of lamination (inserting a celluloid material layer between two sheet of glass). The latter process was invented and developed by the French scientist Edouard Benedictus, who p tented his new s fety gl ss under the n me of “Triplex” in 1910 Contract ENK6-CT1999-SWIFT

2.1.17 Mies; Barcelona Pavilion th

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patented his new safety glass under the name of “Triplex” in 1910. With the new architecture in full flood, the industry was creating the products needed to make the new dreams come true. This technical revolution was in fact accompanied by a renewal in the architectural language, in particular in Germany with the constitution of the Deutsche Werkbund in 1907 and works such as Bruno Taut’s 1914 Glass Pavilion or Gropius and Meyer’s Fagus Factory, dated 1911, in which a new form of vision was intellectually based on the belief that glass was the central material symbolising the architecture of the future. Central to this thinking was Paul Scherbaart and his book Glasarchitektur, published in 1914, which settled out a programme for the use of glass in the new projectual vocabulary, an agenda for the future that represents an 2.1.18 Chareau; Maison de Verre, Paris extraordinary imaginative leap for the potentials of the material: “We live for the most part in closed rooms. These form the environment from which our culture grows. Our culture is to a certain extent the product of our architecture. If we want our culture to raise a higher level, we are obliged, for better or for worse, to change our architecture. And this only becomes possible if we take away the closed character from the rooms in which we live. We can only do that by introducing glass architecture, which lets in the light of the sun, the moon and the stars, not merely through a few windows, but through every possible wall, which will be made entirely of glass – of coloured glass. The new environment, which we thus create, 6 must bring us a new culture” . After the war, the impact of glass started to further accelerate. In 1914, Mies van der Rohe, after having been a rather classical/vernacular designer, began to subscribe to the new aesthetic thinking becoming a directive member of the radical Novembergruppe. By 1919, he had designed an entry for the Friedrichstrasse competition in Berlin. His proposal represented an amazing shift, both for him and for architecture: an angular glass tower, who was then followed, in 1922, by an entirely conceptual project, a glass skyscraper with an amoebic plan. The glass technology implicit in those two projects, the curtain wall as a suspended assembly, was not to be available for half a century more; nevertheless, those two projects represent a testament to the power of a concept that is still vital nowadays.

2.1.19 Corbusier; Ville Savoye, Poissy

The 1920s saw wonderful exploitations of the new materials in the achievement of this innovative aesthetic. A demonstration of this change of attitude is represented by small projects such as, for example, the Tugendhat House of 1930 or the Barcelona Pavilion, built for the 1929 International Exposition, where the continuous flow of space, as well as enclosure, was obtained by the use of glass with as little interruption from framing as possible (2.1.17). By that time, Walter Gropius was creating the Bauhaus, which drew its spirit from the new architectural language, producing an architecture of glass walls for its new headquarter in Dessau during 1925-26. Other masterpieces of glass architecture date to the same period. In 1931, in the Paris Latin Quarter, Pierre Chareau was producing the Maison de Verre (2.1.18), a building of small size but of enormous technical virtuosity, which used glass in an exemplary way, with its steel supporting structure and translucent brick wall. In 1929, Le Corbusier had produced the Ville Savoye at Poissy, not far from Paris, in which the elevations built out of white planes and the long horizontal windows, with their huge pieces of plate glass, merged into a wonderful piece of plastic geometry (2.1.19). Le Corbusier’s projects, moreover, were starting to incorporate some of Scheerbart’ ideas; in the Cité de Refuge, for example, the architect designed a so-called mur neutralisant, a multiple glass wall within which Contract ENK6-CT1999-SWIFT

2.1.20 Wright; Johnson Wax Building

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tempered air flowed neutralising the effect of the cold or the solar heat outside. Unfortunately, because of omissions dictated by a low budget, the result was a technical failure, but, anyway, this intuition pointed the way to a future architectural skin, with multiple functions and which exploits glass in new ways. In the meanwhile, across the Atlantic, the potential for new technologies in general, and for glass in particular, was creating a new styling mood; the Johnson Wax Administration Building, designed by F.L.Wright in 1936, is just one of several exempla (2.1.20). By 1938, Mies van der Rohe was settling into his position as the director of the architectural department of the Illinois Institute of Technology with a great new architectural commission: to design a campus for the Institute itself. New explorations in the field of both the potential of pure transparency and, very differently, the formal potential of the glass skin had started. The Fransworth House of 1946-51, a greatest minimalist statement for a house, and the Crown Hall, of 1954-6, one of the th undisputed masterpieces of 20 century architecture, with its envelope entirely plate glazed, clearly express this new approach to architecture, in which glass becomes almost superfluous, serving only to mediate between the external environment and the occupied space within. At the same time, Mies was also producing high tower buildings, which were to have much greater, and maybe questionable, influence on the forthcoming architecture. With the Lake Shore Drive of 1948-51 in Chicago, and the Seagram Building, dated 1954-8, in New York, in fact, Mies realised the objective for glass architecture set out with the Berlin projects in 1919-21, but in terms of simple orthogonal forms rather than the faceted multiple-reflection of the earlier proposals. In the Seagram Building, moreover, Mies experimented with tinted glass, using a selenium glass which complemented the bronze of the framing and panelling of the curtain wall; the aesthetic idea was really ambitious, the glass varying in its hue according to the time of the day, from pink to blue bronze, as daylight and sunlight conditions change (2.1.21).

2.1.21 Mies; Seagram Building, NY

2.1.22 The Float Glass process

However, a part the work of the “masters” of modern architecture, with the new products on the market, glass started to become part of the architectural scene at every level. The idea of the “picture window” was added to the vocabulary of the domestic architecture, the plate glass shop window, uninterrupted by framing, became the natural instrument for marketing wares in the high street, while a “young” version of the curtain wall became the easy way to clad the new multi-storey commercial buildings. However, to fully exploit the true potential of glazed architecture, after World War II, another technical revolution was to come. In 1952, the Britain’s Pilkington Brothers Ltd. developed a process that combined the brilliant finish of sheet glass with the optical qualities of plate glass: the float process, a milestone in modern glass architecture In this process, a continuous ribbon of glass moves out of the melting furnaces and floats along the surface of an enclosed bath of molten tin. (2.1.22). The semi-molten ribbon is held in a chemically controlled atmosphere at a high temperature for a long enough time for the irregularities to flow out and for the surfaces to become flat and parallel. The ribbon is then cooled down, while still advancing across the molten tin, until the surfaces are hard enough for it to be taken out of the bath without the rollers marking the bottom surface; so, a ribbon is produced with uniform thickness and bright polished surfaces without the need for further processing. The era of modern glass technology had begun.

2.1.23 Rotterdam World Trade Centre

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Starting from those technological advances, the last third of the 20 Contract ENK6-CT1999-SWIFT

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century has seen a dramatic change in the way architects, designers and glass-makers have thought about glass, and not only in its simple flat form. Machines have been improved and perfected to produce endless ribbons of sheet glass; also developed were processes to strengthen glass through thermal and chemical tempering, to curve it, to add tints for reduced heat transmission and glare, and to coat glass with transparent metal oxide films (low-Emission coatings, solar shields, etc.), thus creating a rich and expanding palette. And evolution went on further. In the 60s and 70s, coated glass began to appear in the market, principally in hot and sunny climates, to absorb or reflect away unwanted direct solar energy radiation. However, this evolution was even a consequence of a series of “failures” in the use of glass, that, in the post-war period, international architecture had started to experience worldwide.

2.1.24 The United Nations Logo

In the 50s, in fact, the totally glazed office building as a type started to come of age, partly because of the burgeoning demand for space for office-based activity, partly because of the development of the rental sector in office accommodation that required an “universal” space suitable for a wide variety of user, and partly because of the programmes of postwar urban regeneration in some European major city (2.1.23). However, even if those buildings were often being designed by good, and sometimes great architects, a more insidious form of glass architecture, similar in superficial appearance, but fundamentally different in quality of concept, was being created. Basing on carefully judged investment calculations, the brief for office buildings was clear: maximum office floor area, with the greatest flexibility and “lettability” of use, the greatest available window area, and for the lowest cost. The curtain wall, with its slenderness, cheapness and off-thepeg quality, was an ideal response to those needs. But contrary to its historical architectural concept, as the expressive separation of a light wall from the heavy structure behind, the principle of the lowest common denominator, the mass marketing, its ubiquity, blandness and poor performance, led the curtain wall to a despised result, generally associated with the general opprobrium to which modern 4 “International Style” architecture was increasingly prone . Nevertheless, all this would not have been so awful had it not been for the intrinsic technological weakness in energy performance which these external “heat skins” incorporated. Generally single-glazed, high in their energy consumption, often too cold in winter and too hot in summer, often poorly maintained and dirty, those buildings seemed not caring about the nature of architecture, or the beautiful integration of design and technology, while the users, the office worker occupants, were not a matter of major interest by commissioner and architects. Hence, despite being seen as an ideal component in the newly expanding sector of commercial office development, soon the intrinsic weakness of the curtain wall was identified. And if any good came out of the Oil Crisis of 1972, it was the increase in the realisation that such thin glass skins were wasteful and inappropriate, because of financial and environmental concerns, but also because of comfort and health.

2.1.25 Perrault; Hotel Industriel, Paris

For these reasons, in the last 25 years, taking awareness of the problem of a controlled and optimised use of solar energy inside inhabited spaces, a new interest developed in how to use glass more wisely. The energy crisis and the emergence of ecology and of the concept of a Sustainable 7 Development as a relevant subject for architects had a slow but profound impact, with the lasting effect of a new thinking about building and materials performance (2.1.24). Those new attitudes have seen the expanding of the boundaries of Contract ENK6-CT1999-SWIFT

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architectural design, inspired sometimes by an environmental approach, sometimes by the inspiration of the material itself with brand new performances (2.1.25), and sometimes by the elegant fusion of the two (2.1.26). Environmental control, structural potential, the sheer enjoyment of the surface and the ambiguous materiality of glass, have alternated on the scene of contemporary architecture, while the increasing sophistication of the market, the proliferation of techniques to enhance performances, and the developments of alternative technologies (glass fibre, resin filled units, acrylic tubes, liquid crystals, aerogels, and, of course, chromogenic glazing) have placed a new vocabulary in the hands of the architect, as well as a new and onerous requirement grappling with the imperatives of performance, comfort, well-being, environment, energy use, resources and ecology.

2.1.26 Foster; Carré d’Art, Nimes

These guidelines are then actually intended to provide the designer with some additional information about the correct use and integration of this new technological palette in architecture.


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Chromogenic Glazing: Electrochromic and Gasochromic devices

Advanced glazing materials coming from scientific experimentation offer a wide range of options to enhance the optical and thermal characteristics of windows, and to improve comfort, appearance and the energy related performance of building envelopes; a broad and world-wide interest can be 8 predicted for the use of such technologies . Amongst others, today the first products from long years of material research are becoming available, which can adapt dynamically to the changing external climate conditions or can be switched according to 9 internal needs of users. The so-called “chromogenic” materials , in fact, are able to change their optical properties in response to external stimuli, such as an applied electrical field, ion insertion, light intensity or temperature, thanks to particular physical and chemical properties. The kind of variations that characterises chromogenic devices allows a transformation of the material, from a highly transmitting state, through a partially reflecting one, to one absorbing or scattering the whole solar or visible light spectrum. When this change is sufficient in magnitude, then the material may be useful for building and solar applications. Basically, regarding their properties and the activating factor, we can distinguish between “adaptive” types – Photochromic (responds to light intensity), Thermotropic and Thermochromic (respond to temperature) – that present the potential advantage of being self-regulating, and externally activated chromogenic “switchable” materials – Liquid Crystals, Dispersed Particle Devices, Gasochromic, Electrochromic – that, on the other hand, have the advantage of user control. Switchable materials, in fact, can be directly operated or be linked to the Building Management System (BMS), so as to respond continuously to external weather conditions (outside temperature, solar radiation), to variable factors inside the building (indoor temperature, lighting levels, internal loads), and to occupant preferences 10 and needs . Amongst the emerging “smart glass” technologies, Electrochromics (EC) and Gasochromics (GC), which can be actively controlled to modulate solar radiation, appear to be the most promising in terms of meeting broad daylighting needs and are, probably, even the most advanced as markets products; on the other hand, other technologies (Photochromic, Thermochromic) may be well suited for specific niche building applications. In any climate or situation where window-related electricity consumption and cooling peak demand are high, they may show significant benefits. In fact, they can dynamically modify their visible and total solar energy transmittance, driven by either lighting or cooling needs, thus reducing the total energy consumption, while always maintaining unrestricted visibility, which can be healthy for occupants, both ergonomically and physiopsychologically. Electrochromic glazing exploits the ability of some materials to accept or shed ions, thus influencing the transmission properties in the visible and NIR (Near InfraRed) radiation range. This phenomenon takes place in many inorganic and organic substances (through oxidation or reduction reactions), generally coated in thin (200300 nm) transparent layers. Tungsten oxide (WO3), for example, is an electrochromic material that is subject to most testing at present, because it has the greatest variation of intensity in the visible range, between transparent and dark blue. An EC device consists of different layers (three to five), each with particular properties and functions, placed between two substrates - glass or plastic - that are coated with transparent conductors (TCO).

2.2.1 Structure of an EC device

In a three-layer system, the central layer is an ion conductor (electrolyte), Contract ENK6-CT1999-SWIFT

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which is enclosed between two other thin films, an electrochromic film (electrode, WE) and an electron accumulator, or ion storage film (Counterelectrode, CE) (2.2.1). When a voltage is applied to the TCOs, an electrochemical reaction occurs in which ions are inserted or extracted from the EC layer, leading to a variation of the electron density in the electrochromic material that results in a modulation of optical properties and in the modification of the material 11 chromatic spectrum . A small potential difference is all that is required to trigger a change in state. Moreover, the device exhibits open circuit memory, so that the optical properties remain stable after turning off the voltage; in other words, once the regulation has taken place, there is no need of a continuous supply of the electric field.

2.2.2 The Flabeg E-Control® Glazing

When employed in a Double Glazed Unit (2.2.2), the standard composition comprises a laminated EC float glass outer pane (9 mm), a gap between the panes with argon filling (16 mm) and a heat-insulation low-E coated inner pane (4 mm). The thermal transmittance, or U-value (W/m²K), can vary from 1.6 to 1.1, while the soundproofing value achieves Rw 35 dB; as a consequence, EC devices not only offer protection against solar overheating in summer, but also ensure thermal insulation in winter. The darkening/bleaching process is, in general, adjustable for different light transmission values, τV= 0.52-0.16, corresponding to g= 0.40-0.16. When the tint of the glazing darkens, the transmitting radiation maximum is shifted, thereby causing the electrochromic glass to take on a pleasant blue hue; thus, the quantity of radiation let through is especially filtered in the infrared spectral range. 2

Energy consumption is less than 0.5 Wh/m for a complete cycle, and the darkening/clearing process is continuous and silent, taking up to 15 2 12 minutes for a maximum size pane (1.20 x 2.00 m ) . Gasochromic fenestration systems consist of three main components: a gasochromic Insulating Glazing Unit (IGU), a gas supply unit and a control unit. The optically active component of a gasochromic IGU is a film of WO3, which is coated with a thin film of a catalyst and located on the inner surface of the outer pane of a double or triple IGU. A double glazed GC unit (DGU) - currently with a maximum area of 1.5 × 2 1.8 m - comprises a WO3 coating on surface 2 of a tempered glass and an uncoated 4 mm float glass in a 4-8-4 configuration. For a triple glazed GC unit (TGU) a low-E coating is added on Surface 5 in a 4-8-4-16-4 configuration (2.2.3). When the GC film is exposed to a low concentration of hydrogen, H2 (well below the combustion limit of 2%), in a carrier gas of argon or nitrogen, it colours blue, reducing, for a DGU, the visible transmittance (τV) from 67% to 16%, and simultaneously the solar energy transmittance (τe) from 60% to 12%.

2.2.3 Structure of a GC device

For a TGU with improved heat insulation, visual transmittance (τV) reduces from 61% to 12%, while the total solar energy transmittance (g-value) changes from 48% to 16%. On exposure to a low concentration of oxygen, O2, the WO3 film bleaches to the original transparent state; switching occurs within 2 to 20 minutes, according to the gas supply rate. In a Triple Glazing Unit (TGU), the gas mixture is introduced into the cavity between the outer and middle panes. The second gas-filled cavity and third pane, which has a low-Emissivity coating, ensure that the IGU has good thermal insulating properties (low U-value) (2.2.4). Contract ENK6-CT1999-SWIFT

2.2.4 The Interpane GC TGU

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The gas supply unit consists of an electrolyser and a pump, and is connected by pipes to the window in a closed-loop configuration; the gas supply unit is integrated into the external building façade. One gas supply unit is able to provide sufficient gas to switch several 2 gasochromic modules (typically 10 m ). The control unit allows both manual and automatic control, it can be mounted wherever convenient within the room, and, as a future option, it could be integrated into a Building Management System, allowing the switching unit to optimise lighting conditions, thermal comfort and/or 13 building energy consumption .


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From passive to dynamic devices: environmental and aesthetic concerns

Dynamic switchable devices can incorporate some of the innovative materials mentioned above, providing new building components for controlling solar gains and daylight, according to the prevailing weather conditions and user requirements. A switchable façade can be designed to adapt in an almost “living” way to changing light and weather conditions, so as to reduce the energy consumption of the building, to create a pleasant environment for the people who live and work inside, and to make use of natural, renewable energy sources in as environmentally compatible 14 a way as possible . The building has to be manned with the ability to change its functioning to adapt itself and its users to the changes in the environment. In a sense, we may say that a building equipped with dynamic ‘active’ (or ‘inter-active’) devices should be able to behave like a person would do under changing circumstances. Actually, having compiled a knowledge base through constant trial and error, people know how to react to changes. When the weather gets cold, a person reaches for a jacket, acknowledging that, by having an insulating layer between his body and the environment, he would reduce his heat flow to the surroundings. On the other hand, when the weather is warmer, the knowledge base suggests a light sweater will do, so as to “help” his physiology to cope with a greater amount of energy.

2.3.1 The human skin

With the same freedom and creativity that characterise a person facing changeable events, thus, an “advanced” façade should not be designed as a self-referential object, but rather as an environmental filter able to enhance exchanges between the inner microclimate and the outer macroclimate, activating consequently differentiated strategies to “adapt” to different conditions, climates and functions and thus minimising its energy demand. This concept is based on the idea that a building is a little like a “third skin”, the first being our epidermis, and the second our clothes. If the former is only barely adequate, people experience discomfort and are eager to 15 employ energy consuming devices to improve their thermal condition .

2.3.2 The human eye

With the application of a biologic metaphor, hence, it is clearly understandable the reason why it seems more appropriate to describe the enveloping membrane as the “building skin”, thus emphasising its close 16 relationship with the human epidermis . Actually, the human functions performed by the skin and the eye represent really good models for how we would like the building envelope to behave, since they perform complex, involuntary and intuitive functions. The human skin (2.3.1), the largest organ of the human body, adapts to temperature and humidity helping the body to regulate heat; it can feel a breeze or the slightest touch, and, upon needs, it can repair itself; it is waterproof and, yet, permeable to moisture; it protects the rest of the body from toxins, injuries, the sun, and temperature extremes in the external environment; it preserves the stability of the body's inner environment and keeps it in place; it communicates information about physical and emotional states, betraying emotions by blushing (embarrassment), turning red (anger), blanching (fear), sweating (tension), and forming goosebumps (terror); it provides identification through unique finger and sole-prints. On the other hand, the human eye (2.3.2) is a fantastic example of extreme adaptability; it is provided with a lens that is able to self-adjust (intelligent auto-focus), responding to signals coming from the brain telling it what to look at; a shutter stops up and down so as to look after the changes in light levels; automatic lubrification keeps it clean and moist; an eyelid provides a form of ‘black out’ and shuts down when we need to sleep or to protect 16 the eye, by closing in a fraction of second, if danger is sensed . Contract ENK6-CT1999-SWIFT

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The emphasis, thus, lies on the active, dynamic and adaptive functions carried out by the building envelope, a very different issue compared to the conventional passive and static architectural approach that seems to have oriented for a long time the design of buildings. The truly dynamically-active switchable building skin, then, has to be a filter that actively regulates instead of passively protects. Rather than being a statically inert envelope, it should be provided with some of the human characteristics giving it the ability to learn, adjust and respond instinctively to prevailing immediate environmental stimuli; a variable, adaptive and dynamic membrane, self-regulating in a flexible way, able to provide security and privacy, access and views, modulate the flows of energy (light, heat) and guarantee comfortable internal conditions with a more efficient use of energy. Moreover, bringing to the extremes this biological metaphor, we may even say that the basis for this consideration 16 also contains the analogy of “evolution” . Actually, proposing the application and the integration in architecture of switchable materials providing a ‘responsive’ system that can physically react to external variations, so as to improve building energy performance and internal comfort, simply extends ideas and principles that accord with the proposition of Darwin, who held that the capacity to survive depends 16 on the ability to adapt to a changing environment (2.3.3). The animal and vegetal world teaches us that the species which survive are those who live in the environment of the planet with the least effort, i.e. those that have evolved creating a metabolism able to maintain life with the least expenditure of energy: food and waste balance each other, while the necessary energy is provided by the sun. According with the 16 alternating seasons, the animal coat moult, trees lose leaves . The ideas we are trying to emphasise now attempt to integrate the notions of adaptation to the environment as seen in natural evolution, with the concept of environmental responsibility. Evolution and adaptation are fundamental to life, and are strictly bound to an ecological design process. If the “ecological” aim in building design is to make an effort to reduce the total primary energy needs to a minimum, and ideally down to zero, by using only renewable resources to ‘feed’ a building’s comfort system, this balance has to be achieved at any climate and in any condition. This aim provides a conceptual, and maybe even aesthetic - as we will now try to explain - basis for the advanced buildings of the near future, as well as one concerned about the efficient management of natural resources and the environmental impact.

2.3.3 Animal and vegetal adaptation

Nevertheless, even though the spread out awareness of those concepts, built environments have been evolving so far in a rather opposite direction. It is, in fact, now well established that buildings pose a major load on the environment: the potential risk posed by the greenhouse effect and the resulting impacts on climate change, the damage being inflicted on fragile ecosystems by increasing development and resource extraction, the decrease of traditional fossil-based fuels, the depletion of the ozone layer, together with a general environmental deterioration, are all major problems st facing us at the beginning of the 21 century (2.3.4). Indeed, it is obvious that a correct integration of innovative interactive devices, together with an ecologically driven attitude in the way in which we conceive our buildings, both directly and indirectly, could have a priority role to play in the collective efforts required to avoid a possible significant catastrophic environmental degradation. However, before getting on with this issue, it is important to stress out another essential concept: when we talk about ecological concerns related to building design, the aim of the task is about more than “just” saving Contract ENK6-CT1999-SWIFT

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important energetic and natural perishable resources. Architecture always expresses a point of view, a perspective, but it also 17 must involve an ethical way of behaving in relation to the environment . For all of these reasons, more than ecological design, we have been talking about sustainable design, where the term “sustainable” is intended to add also the dimension of time. A sustainable development implies, hence, an ecological approach that includes also a great responsibility to the future, according to its definition 7 as to “keep in existence, prolong and maintain” . As we get to this point, however, other questions arise: aesthetics, beauty, health, well-being and quality of life can be said to be as important to an environmental approach as are energy consumption and resource depletion, since a building cannot be considered to be really “sustainable” if it is not also a pleasant place to live and work in. Therefore, more advanced forms of building ‘life’ are needed to meet the whole of the physical, physiological, and psychological human needs, but always in a strict connection with the environment that houses and “sustains” them. To accomplish those objectives, however, the problem cannot rely only upon technological issues, but rather it is referred mainly to the realisation of building envelopes able to weave together the triad between environmental, architectonic, and human considerations, into an ecological - or better, as matter stands, sustainable - approach to design. As these three layers are integrated, we move toward the realisation of a “living architecture”, one that more fully supports and engages life in all its forms. According with Alvar Aalto: “In recent decades, architecture has often been compared with science, and some have tried to make its methods more scientific, even to transform it into pure science. But architecture is not a science. It is still the same great synthetic process, a conglomeration of thousands of significant human functions, and it will stay that way. Its essence can never become pure analytical. Architectural study always involves a moment of art and instinct. Its purpose is still to 17 bring the world of matter into harmony with human life” .

2.3.5 Winged Victory of Samotrace

In any case, the introduction of “dynamically-acting” systems, will surely have first of all a dramatic impact on our traditional aesthetic conception of buildings, here intended as the expression of the architect’s creativity. Architectural space, in fact, will no more be just a container delimited by walls, but rather it will become a “scene” of the various interrelations between man and its environment; a vibrant, harmonious whole able to change according to user needs. So, what was previewed forty years ago by the intriguing and prophetic Marshall McLuhan finally becomes true: buildings will be similar to a complex nervous system, sensible entities to interact with, “objects” that may adapt to our ways of inhabiting spaces, becoming for us a real “third skin”. In other words, sustainable buildings will start to become part of the ecological system they are in contact with.

2.3.6 V.Kandinskij; Black Bow

But if space is transforming into a series of interrelations, it does not make any more sense to talk about “form” in its classical sense, i.e. as the abstract crystallisation of an idea, as the Greek representation of beauty, the Winged Victory (Nike) of Samotrace, for example (2.3.5). Therefore, what is brought into question here is one of the main postulates of the historical western culture: the conception of the aesthetic object structured as a moment of opposition - a “perennial monument”, aere perrenis, the Latin poet Oratius would say - against the temporariness of existence. Thus, no more matter to be perceived just by the sense of sight, that has the tendency to freeze the complexity of reality in abstract and lifeless images - the absolute eye-centred Alberti perspective - but rather an organism founded upon the involvement of the whole of the senses, Contract ENK6-CT1999-SWIFT

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that work together and that, in their turn, determine further transformations 18 and even the opening of a new significance . By the way, we have to admit that the artistic research - that has always anticipated the architectural one - has been working on those subjects since more than a century. Actually, the concept of an interactive coloured light has already fascinated Impressionist painters such as Claude Monet, who - in the series he devoted between 1892 and 1894 to the Cathedral of Rouen, ranging in effect from dawn to sunset, or in the canvas he painted of the House of Parliament in London, during 1904-05 - by providing a static subject under different light conditions, illustrated how the changing “envelope” of light can radically transform the way in which we perceive the reality. Then, if we think at the works of the Abstract painters, as Vassilij Kandinskij - with his Black Bow (2.3.6), 1912, or Yellow, Red, Blue (2.3.7), dated 1925 - we become fully aware of the attempt to represent with the vibrant, energetic composition and powerful expressionistic colours, exalted by the tension of black outlines, the kinetic rhythms of life, i.e. the fulfilment of our perceptions under the aspects of space and time. These first experiences had, of course, a huge influence on the artistic debate of the time, and clear examples of those new theories may be traceable in other movements, as the Dadaist - with works such as Marcel Duchamp’ Rotoreliefs (2.3.8), 1935, or the Bicycle Wheel (2.3.9), 1964 (original 1913) - as the Futurists - like Umberto Boccioni’s Unique Forms of Continuity in Space, dated 1913, where the figure strides forward vigorously - or rather as the Constructrivist - like Nuam Gabo’s Kinetic Construction (Standing wave, 1920), a sculpture that becomes visible as a wave-like, three-dimensional form only when its vertical metal rod is made to oscillate. The essential subject of those works of art, therefore, is not any more beauty intended as a static interpretation of a form, but rather a new dimension in which space and time merged together: the Movement.

2.3.8 M. Duchamp; Rotoreliefs

2.3.9 M. Duchamp; Bicycle Wheel

As Nuam Gabo declared in his Manifesto, printed in Moscow in 1920: “We proclaim: for us, space and time are born today. Space and time: the only forms where life is built, the only forms, therefore, where art should be erected. We renounce the thousand-year-old delusion inherited from Egyptian art that held the static rhythms as the only elements of the plastic and pictorial arts. We affirm in these arts a new element: the kinetic 19 rhythms as the basic forms of our perception of real time” . Naturally, some of those intuitions have also appeared in the field of architectural and urban experimentation, especially during the 60s and the 70s: the Archigram in England, the Metabolists in Japan, the Situationists in France, ArchiZoom and SuperStudio in Italy, or, more recently, the urban sculptures of Richard Serra (2.3.10). Nevertheless, it is only nowadays, thanks to major technical instruments and a more intense research effort, that those concepts seem to have the chance of finally becoming concrete productive occasions even amongst the building industry. For this reason, we could say that with the development of variable interactive devices, the “form” in itself, might be considered as a heritage of the past. On its place, we may assume the more “plastic” and sustainable (in its wider sense) concept of interrelation, that implies the sensorial - and thus, aesthetic - involvement of the user, the architectural object and its context, into a process founded on a mutual exchange of 18 information . Obviously, from the expressive point of view, there could be projects that regarding those arguments may set up an architectural image and others that may rely upon technological details, but certainly they represent one Contract ENK6-CT1999-SWIFT

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of the most promising issues of contemporary and future architecture. It means that achieving energy efficiency in a design will not necessarily have to be entirely prescriptive and narrowly functional the way sometimes it could be thought. This will refer not so much to the way in which a switchable façade will reflect the functions taking place behind it, but rather to the way in which it will interact with changes in the climate. The classic architectonic idea that the façade is representative of the building's function is being transformed. In fact, with the introduction of the climatically active building, the façade will assume the role of a dynamic environmental filter, making a significant contribution to the highly evolved building of the future - designed and equipped to take advantage of the new technologies - and laying the aesthetic and functional foundations for a new architecture, bio-climatically oriented, technologically competent, 16 environmentally conscious and with new forms of beauty .


2.3.10 R.Serra; Intersection, Basel

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The Integration of Switchable Glazing in Daylight Design

Of all the materials used in building, glass is the one that has the highest symbolical value, not least because of its direct and intrinsic rapport with light, which can pass through it as well as be reflected from it. Rather, as Le Corbusier stated long time ago, just light may be considered the truly raw material of architecture, as sound is that of music, presenting, at an aesthetic level, the architect with unique opportunities. The way in which glass behaves in relation to light (and energy) is, thus, fundamental 4 to its success, but sometimes even to its failure . As a consequence, critical consideration of switchable devices as building materials leads to the conclusion that, although they have many marvellous properties, they are not without their limitations, so a wise control of their use is fundamental so as to obtain the kind of benefits we have been discussing so far; obviously, this applies especially in terms of a correct integration of innovating dynamic devices in daylight design.

2.4.1 Corbusier; Ville Savoye, Poissy

Optimising large glazed objects to conserve energy and to provide visual and thermal comfort is always a major engineering and architectural challenge. Defining the “right” permeability of a switchable device at any time and under any sky condition, in fact, requires that planners and builders reach a compromise, because the ideal visual and solar transmittance from the point of view of energy balance and building operating expenses depends on adjustable variables, while many other parameters have to be considered in order to create comfortable conditions inside buildings. In addition, it must be considered that the success of a window in general goes far beyond the “arid” quantification of standard performance criteria such as the visible light transmittance or the total solar energy coefficient (2.4.1). How a transparent opening frames a view, admits the smell of fresh air after a rainbow, creates a particular effect of light, or connects inhabited inner spaces to the beating of the outside life, all have cultural and social meanings impossible to quantify; the consideration, or rather the ignorance, of those issues amongst our design criteria will then be the starting point to define the role and the prevalence of technology in 4 buildings (2.4.2).

2.4.2 Daylight in a L.Kahn Architecture

Therefore, a good daylight strategy should maximise the potential of architectural form while taking advantage of technologies to further refine and enhance solutions. For this reason, it is important to always consider and design switchable glazing just in terms of a technological advance that holds the promise to provide variable glazing characteristics within a single system, and not as a panacea that could solve all the problems generally related to a wrong daylight design. In order to reach this level of control and interaction with the environment, it is of fundamental importance that a good level of integration is realised between people and technology, and amongst the hardware and software elements that, both in natural and artificial forms, compose a complex daylighting system. Anyway, the use of the term control when discussing about daylighting design does not mean to create a technological system that can restrain, tame, regulate or dominate natural forces. Rather, daylight technologies have to be perceived as the opportunity to create a conversation between the natural and the built environments, modifying, altering, or shaping natural light, and integrating it into an overall (day)lighting strategy (2.4.3).

2.4.3 Foster; Carré d’Art, Nimes

Naturally, this is of even major importance when talking about switchable devices that can continuously alter their visible light transmittance, reflectance, thermal capacity, transparency or translucency, and even the colour of glazing, thus revealing to the room they envelope always different 2.4.4 Libeskind; Jewish Museum, Berlin f Contract ENK6-CT1999-SWIFT

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levels of contact to the external world. The goals of a daylight strategy can be defined from a great variety of points of view, that may consider ecological issues (energetic and natural resource depletion, environmental impact), tasks and activities (lighting needs in both qualitative and quantitative terms), systems integration (lighting, HVAC, etc.), human experience (visual and thermal comfort, healthiness, orientation in space and time, connections to the outdoor, etc.), aesthetic considerations (form, dimension and articulation of spaces, materials, etc.), as well as other concerns. Logically, it may not be possible or even necessary to address each of those objectives simultaneously; yet, analysing their potential can clarify design intentions, determine 17 priorities, and reveal potential trade-offs and/or contradictions . For several centuries, as a matter of fact, the presence of daylight in inhabited constructions has performed as a measure of time, varying in direction, angle and intensity depending on the place, the season and the time of the day, thus giving fundamental form to man’s sense of space. The daylight, drawn through openings into the interior of his built structures, enabled man, who dwelt inside, to understand his own being and the relationship that bounded him to nature. The close relationship existing between the rich play of natural light and the creation of architectural spaces, moreover, has always been seen, in a sense, as a sort of condensation and purification of its mystical power, while the wise presence of light, of a brilliant shaft penetrating the profound silence of darkness, has often been interpreted as an evocation of the sublime or even as a call for the divine, in opposition, perhaps, to the darkness world inhabited from men (2.4.4).

2.4.5 The Doric Temple in Segesta

2.4.6 The Erectheion in Athens

On the other hand, this search for light translates an ancient and diffuse tendency to “dematerialization”, a tendency that is already traceable, for example, in the Greek culture within the passage from archaic temples of the 5th century BC, as for example the Doric Temple in Segesta (2.4.5), up to the following constructions belonging to the “Classical Age”, as the Erechteion in the Acropolis of Athens (2.4.6). Through history, we can find rich examples of transcendent or spiritual qualities in architectural daylight. Gothic architecture, more than perhaps any other style, explicitly used daylight for its spiritual effects; thanks to the natural enlightening of spaces, with the vibrant and colourful changing spaces determined by rose windows, it may be described as a transparent, diaphanous architecture, a continuous sphere of light. Or we may refer to th some of the masterpieces of Italian 16 century painting, as, for example, the Caravaggio’s Calling of Saint Matthew (1599), in which the presence and the actual calling by the God is symbolically represented by a sudden shaft of light entering the scene (2.4.7).

2.4.7 Calling of St. Matthew - Detail

Notwithstanding that, in modern times, although glazing technologies have augmented their performances increasing the transparency of buildings, occupants have become further removed and disconnected from the environment because of non-operable windows and artificial technological means of providing lighting, heating and cooling, while the need of masking the glazing by opaque shading devices, so as to guarantee comfortable conditions inside living spaces, has often caused the 20 transparent box not to be transparent any more (2.4.8). In addition, from an aesthetic point of view, liberating windows from any structural limitation and allowing them to be freely constructed in any size, has not meant at all the liberation of light in architecture; rather, its vitality, once groomed with infinite care, has been allowed to scatter ineffectually, and be lost, hence producing a world of exceeding brightness, a world of homogeneous light that has eventually meant the death of space as surely as absolute darkness. So, we move toward a paradox, seen in much Contract ENK6-CT1999-SWIFT

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modern architecture, where, rather than erasing the boundaries of the building, the layer between inside and outside has become increasingly impermeable, leading to a dissociation from the external world - physically, environmentally and socially - with the result that one is no longer made to feel the individual character of a place. However, just because the use of technological devices facilitate to minimise the separation between interior and exterior spaces, it does not mean that this is necessarily always desirable; actually, the degree of environmental distinction or union always results from the combination of functional, experiential, and conceptual issues. For such reasons, it is of fundamental importance that architects reconsider the role of natural light, carefully leading it into the interior of built spaces so as to inform space with depth, and produce richly stimulating places. On the other hand, it must always be kept well in mind that daylight is not only a resource and a vital sustenance, but also a force that can create meaningful architectural experiences; the moods and the quality of an architectural space can broadly vary with its daylight levels and conditions, even transforming sometimes a dark, sober, and oppressive place into a captivating, enthralling, and polychromatic one (2.4.9). Further more, the scientific research has recently proven the close relationship existing between a correct and controlled income of daylight, indoor conditions, health, well being, and our perception of the environment. A good and balanced daylight level, with its variations and its spectral composition together with the provision for external views, in fact, is one of the main factor of indoor comfort that can positively influence health and productivity, while, at the same time, reduce suppressed feelings of panic, anxiety, disorientation and depression (SAD, Seasonal Affective Disorders), and this applies, of course, above all to working 21 spaces (2.4.10).

2.4.9 St. Etienne Cathedral in Caen

Moreover, a correct and studied presence of daylight in our buildings may be one of the most important means of maintaining our biological rhythm (circadian cycle) and connection to rhythms of nature, and a realistic way of marking important daily moments (dawn, morning, noon, afternoon, sunset and evening). Obviously, the occurrence of these luminous events may seem peculiar to a definite moment and place, since they can vary broadly, expanding or contracting according with the season and the geographical location, but, if we are aware of those dynamic patterns of daylight, we may have at disposal a very accurate instrument to orient ourselves in space and time. In fact, when daylight passes through the eye, the signals are carried out not only to the main visual areas but also to the parts of the brain responsible for the emotions and hormonal regulation, that control, for example, the rhythmic secretion of cortisol - the stress hormone - and melatonin - the sleep hormone. Thus, ocular light stimuli from the retina, resulting in signals being sent to the various glands, involve the whole of the physical (energetic exchanges), physiological (transformation of energetic fluxes into nervous stimuli) and psychological (brain interpretations of those stimuli) aspects that together create that “process of perception” assigned to inform us about the characteristics of our 22 surrounding environment . Nevertheless, it is now as well demonstrated that a great part of our social life is temporally organised in relation to a rather “mechanical time”, which is basically independent of the rhythms of our body’s impulses and needs. In other words, we are increasingly deviating from the organic and functional recurrence dictated by the natural colour, angle and intensity of the daylight, and replacing it with the 24-hours artificial timetable which is,

2.4.10 View obstructing lamellae

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17

on the contrary, imposed by the schedule, the calendar and the clock . The reassembling of this paradox passes through the assumption of a new projectual attitude towards the concepts of daylight strategies, in which the integration of interactive dynamic devices can give a huge contribution to modulate the relationship between enveloped spaces and external environment, carefully controlling the right income of daylight, both to ensure a contact with the variable external word, and thus bringing “life” to the building, and to guarantee acceptable comfort conditions to enveloped spaces, both in perceptive and energetic exchanges terms. Therefore, it is, in general, always necessary to be aware of the union between what we have available as natural resources and what we may then control with technological features, so as to obtain the best gain concerning energy consumption, contribution to the user’s satisfaction, 22 well-being and good performance of the visual activities .

2.4.11 Nouvel; IMA, Paris – Internal view

The question, then, becomes how to use this innovating technology, at what scale, and for what purposes. At one extreme, in fact, one may argue that an increased use of advanced technologies in architecture could turn it away from the environment, ecological awareness, and perhaps even from a sustainable future; on the other hand, if appropriately used, it is actually possible that technology could move us forward in an ecologically responsive way. Indeed, solutions with technological and architectural integrity can be found only if the benefits and limitations of innovating technologies are carefully weighted with other architectural strategies (2.4.11). We should always consider, anyway, that technology is not the absolute answer, although it is a fundamental means. Ideally, there is no distinction between an architectural and a technological approach; each approach should be so interwoven with the other that they become inseparable. This is true above all in daylighting designs that successfully combine architectural strategies and technologies for maximum ecological and experiential benefit. Yet, this synthesis is not always achieved, though it is through architectural daylighting strategies, not technology for its own sake, that the greatest ecological, luminous, and 17 human meaning can be achieved . High performance window systems represent an element that is 23 necessary, but not always sufficient, in an efficient daylighting design , especially when dynamic switchable envelope/lighting systems may respond in real-time to temporal changes in sun and sky conditions to control daylight intensity and solar heat gains. In most building applications today, the window performance is considered in a rather “static” way as a single building component (2.4.12). Traditional engineering design, in fact, takes generally a worst-case perspective, analysing performance under peak heating, lighting and cooling conditions. With variable fenestration components, however, 24 design today has to take a more “enlightened” perspective . Not only there can be significant variability in the external climate and associated thermal and lighting conditions, but occupant needs can vary sensibly in interior spaces, in terms of preferences and associated differences in clothing and metabolic levels and in the nature of visual tasks present in a given working environment, while the effects of changing office tasks and changing company business needs should also be addressed. As a consequence, if the desired building conditions should be maintained within relatively constant comfortable ranges, while the external forces can 2.4.12 Nouvel; Cartier Factory, St.-Imier highly change in a relatively short time, what is needed is an innovating Contract ENK6-CT1999-SWIFT

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type of dynamic and interactive control. A clear example may be the situation where daylight external levels vary by a factor of ten in a matter of seconds, as the sun, for example, moves behind a cloud. Given this significant degree of external changes, it is natural that a switchable dynamic glazing system, in co-operation with dimmable artificial lighting, should be endowed with the ability to respond to such variability in order to maintain interior (luminous, in this case) 25 levels at a narrower dynamic range . This kind of consideration upon switchable glazing performance leads to a perspective of glazing and façade systems as an integrated part of an overall building performance. Buildings, hence, have to be designed and operated more as a single functioning system rather than as a collection of loosely coupled distinct parts, so as to avoid the realisation of an uncomfortable and inefficient building that is expensive to operate (both in ecological and economical terms), and theoretically even difficult to retrofit. This integrated approach looks at the consequences of each individual decision on the whole building; beginning from the planning stage, glass and fenestration systems manufacturer should be partnered with artificial lighting systems and furniture suppliers, in order to provide integrated daylight solutions. Building Management Systems (BMS) that control the overall building operations should, therefore, be designed and operated in order to be able to finely tune an interactive façade that can help to modulate heating and 25 cooling loads and lighting energy needs .

2.4.13 H&DeM, SUVA Building, Basel

The settlement of the different systems throughout the day (and the year) will thus consist of a series of trade-offs. Each assessment and optimisation operation must be repeated for the different spaces inside the building on a recurring basis, requiring an extensive control network and automation system, and emphasising the need for models able to predict 24 accurately overall building performance . In terms of daylight design guidelines, as different studies already well 26 explain , in general each task calls for a different need in terms of quality and arrangement of the space, disposal of workstations, furnishings, surroundings, equipment, and, of course, luminous environment. The ambience of a workplace has to go towards the occupants’ requirements, which are defined by cultural, social and educational concerns, and which relate to the functionality, aesthetics and ergonomics of the rooms and their setting. The design must then address and support user’s biorhythms (orientation in space and time); occupants need appropriate visual contact with the external world, with the cycle of luminous events, seasons and weather conditions: quality of the view, size and orientation of the openings, field of view in relation to the surroundings, arrangement of the workplace, visual and sun protection, ventilation, operability of windows, and so on, must always be included in the overall design of inhabited spaces (2.4.13). The workstations and their surroundings (i.e. the whole room) have to be designed in accordance with human needs: users have to be able to concentrate without any disturbance (privacy), and be in the condition of conversing with other room occupants when necessary or desired (communication). The spaces should be organised in order to facilitate the observation of the windows, of the whole room, the entrance and the exit, as well as the activity of the colleagues. Sombre and indistinct zones should be avoided, while everything should be immediately visible (information). The rooms should always offer a certain degree of variation and surprise; lighting then, both in natural and artificial forms, should never distract as a result of being excessive (glare, reflections), not functional Contract ENK6-CT1999-SWIFT

2.4.14 Piano; IMAX Theatre, Berlin

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(position, angle and orientation) or creating an inappropriate atmosphere 26 (light colours and temperature) . Notwithstanding that, daylight does have its drawbacks: direct sunbeams on a task, or diffuse light coming from bright clouds or a reflective building can be the cause for discomfort and glare (2.4.14). In general, the luminance ratios in the field of view must be contained within defined and limited ranges; too large, and the adaptation of our eyes will be difficult; too small, and the estimation of depths and distances can 20 be difficult . The position of the opening in the façade and its architectural composition are also important. An appreciated solution can make use of an opening divided up into two different parts: the upper part can bring direct light 2.4.15 Nouvel, IMA, Paris - Internal view farther into the room or avoid overheating and reflectance on the tasks (if properly masked with, for instance, a switchable glazing in its fullycoloured state), while the lower can be charged of providing an unobstructed view to the outside world. Moreover, a structure, as for example a frame, between the two parts may provide a visual break and, at the same time, the opportunity to attach a light-shelf or a shading device. Dark-coloured elements in the interior part of the façade, such as black frames or shades, should, in general, be avoided, because contrast in the field of view can be liable of the creation of ‘visual noise’ that affect the luminosity ratio of the window, causing the eye to continually adapt (2.4.15). In a horizontal blind system, then, for example, the individual strips should be slim, light-coloured and narrow, for the wider the strips, the larger the 2.4.16 Nouvel; IMA, Paris - Internal view 20 undesirable light-dark patterns . In a working environment, it would be important for each employee to be able to control the overall lighting level and glazing setting according to his (or her) peculiar needs. But since people’s preferences are never the same, nor they do perform the same task at the same time, it would be better to leave the general control to a central system, anyway leaving to the occupant at least a partial over-ride capacity. Actually, the lighting needs of a normal-vision young person will differ broadly from the requirements of an older worker with eyesight deficiencies. Similarly, the lighting required to paper reading or handwriting will be different from what is needed to work at a computer terminal. However, most people are luckily flexible, intelligent and adaptive, and 24 tend to carry out solutions that function . Consequently, management façade systems must provide the same level of adaptability and flexibility by intelligently responding to changing human needs, while preferably always comprehending and “tolerating” some form of occupant control (2.4.16). Regarding artificial lighting systems, it is, in general, the combination of natural and artificial lighting that can create a visually stimulating situation in a working environment. However, it should always be kept in due consideration that the unique feature of daylight is that it is not just light but 20 also a vital source of environmental information . Therefore, the artificial lighting should not be considered as a substitute for poor daylight design, but rather it must be designed to illuminate the space in a good and comfortable way at times that there is no daylight available. Good integration between natural and artificial lighting will make it possible to gradually dim the amount of electric light if there is enough natural illumination, and if its modulated ingress does not disturb in any way interior activities (2.4.17), and thus save energy. Contract ENK6-CT1999-SWIFT

2.4.17 Glare in a working environment

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In the design and installation of the control system for a switchable façade, it would be always preferable to foresee the use of sensors or other devices that could, according to predetermined strategies (lighting levels, occupancy sensors, w-e/holiday, night-time schedules, etc.), regulate the setting of the glazing and the level of artificial light in accordance with the specific needs and preferences of the users, switching on and off in order to control trigger points and fine tuning. Obviously, the whole of these features is not consistent with the simple substitution of the conventional glazing materials with the newly available innovating devices, but rather it must determine a complete reformulation of the entire project, from the environmental strategy up to the detail specific solutions. In this logic, hence, this new interaction between technical equipment, building envelopes and environmental natural forces has necessarily to become a central element in the configuration of spaces, not being absolutely a “bond” for the design, but rather a real starting point for good architecture.


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Wigginton M., Glass in Architecture, Phaidon Press, London, 1996.

5.

Corbella O.D., Corner V.N., “The window relevance for the architectonic design in tropical climate”, in Proceedings of the PLEA 2002 Conference, Toulouse, July 2002.

6.

Scheerbart P., Glass Architecture, Alpine Architecture, November Books Ltd, 1972.

7.

World Commission on Environment and Development, Our Common Future, Oxford Univesity Press, 1987.

8.

Lampert C.M., Yan-Ping M., Fenestration 2000 – Phase III. Advanced Glazing Materials Study, Lawrence Berkley Laboratory, University of California, 1992.

9.

Granqvist C.G., “Electrochromic Coatings for Smart Windows: a Status Report”, in Renewable Energy, 2nd World Renewable Energy Congress, vol.1, Pergamon Press, Oxford, 1992.

10. Lampert C.M., “Chromogenic Switchable Glazing: Towards the Development of the Smart Window”, in Proceedings of the Window Innovations ’95, Toronto, June 1995. 11. Lee E.S., Di Bartolomeo D.L., Selkowitz S.E., “Electrochromic Windows for Commercial Buildings: Monitored Results from a Full-Scale Testbed”, in Proceedings of the ACEEE 2000 Summer Study on Energy Efficiency in Buildings, Asilomar, August 2000. 12. Flabeg Pilkington, EControl®- The thermal multitalent, Architectural Products, 2001. 13. Wilson H.R., et al., “The optical properties of gasochromic layers”, in Proceedings of the 4 Conference on Coatings on Glass, Braunschweig, Germany, November 2002.

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14. Compagno A., Intelligent Glass Façade – Material, Practice, Design, Birkhauser, Basel, 1995, rev. ed. 2002. 15. Travi V., Advanced Technologies, Birkhauser, Basel, 2001. 16. Wigginton M., Harris J., Intelligent Skins, Architectural Press, Oxford, 2002. 17. Guzowski M., Daylighting for sustainable design, Mc Graw-Hill, 2000. 18. Prestinenza Puglisi L., Silenziose Avanguardie. Una storia dell’architettura 1976-2001, Testo & Immagine, 2001. 19. Alley R., Catalogue of the Tate Gallery's Collection of Modern Art other than Works by British Artists, Tate Gallery and Sotheby Parke-Bernet, London 1981. 20. Zonneveldt L., De Groot E., "The Daylight Challenge", in International Lighting Review, Philips Lighting, n. 1/2001. 21. Van den Beld G., "Light and Health", in International Lighting Review, Philips Lighting, n. 1/2001. 22. Fonseca I.C.L., et al., “Quality of light and its impact on man’s health, mood and behaviour”, in Proceedings of the PLEA 2002 Conference, Toulouse, July 2002. 23. Selkowitz S.E., Lee E.S., “Advanced Fenestration Systems for Improved Daylight Performance”, in Daylight ’98 Conference Proceedings, Ottawa, May 1998. 24. Selkowitz S.E., “Integrating Advanced Façades into High Performance Buildings”, in Proceedings of the 7 International Glass Processing Days, Tampere, Finland, June 2001. 25. Selkowitz S.E., “High Performance Glazing Systems: Architectural Opportunities for the 21 th Proceedings of the 7 International Glass Processing Days, Tampere, Finland, June 1999.

st

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Century”, in

26. Kramer H., “Mastering Office Lighting”, in International Lighting Review, Philips Lighting, n. 1/2001.

2.6

Iconography


- Images n° 2.1.6, 2.1.7, 2.1.15, 2.1.16, 2.1.22, 2.2.1a, 2.2.1b, 2.2.2, 2.2.3, 2.2.4 are courtesy of José Flémal (UCL). - Images n° 2.1.18, 2.1.19, 2.4.1 are courtesy of Prof. Arch. Giorgio Peguiron (University of Rome). - Images n° 2.1.20a, 2.1.20b are courtesy of Valérie Mahaut (UCL). - Image n° 2.1.25 is taken from the United Nations Official Web Site: http://www.un.org. - Images n° 2.3.3a, 2.3.3b, 2.3.3c are taken from the Gimp-Savvy Copyright-Free Web Site: http://www.gimpsavvy.com/PHOTO-ARCHIVE/.


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3 Guidelines for architects and end-users 3.1

The need for switchable façades

From linen fabric impregnated with oil up to the most recent technological evolution, glazing options have made some huge strides since people first tried to bring light into interior spaces. Actually, the history of glass in architecture has often left its mark on the very history of architecture itself, and it is far from difficult to understand why. In order to understand and correctly integrate switchable glazing in architecture, it is important therefore to take into account the complex interactions that an actively controlled transparent surface can have with 27 the external solar radiation (3.1.1). As it has been explained so far, a window is one of the most complex components in the overall building structure; it can give us daylight, views, may be opened to let fresh air in, and transmits the sun's energy for warmth. On the other hand, it protects us from rain, wind, noise, burglary and, sometimes, from undesired radiation (ultraviolet, radio waves, etc.).

3.1.1 Foster; Bundestag Dome, Berlin

The heat loss has been substantially reduced through the development of innovative glazing in the past decades. However, there is always a need to find a balance between transmission and protection. Maximal heat insulation results in reduced daylight and solar energy transmission, while maximally transmitting glazing reduce thermal comfort appreciably. A transparent façade, therefore, has always to be designed in order to reflect the needs of the users and the requirements of the building. Having too few windows, for example, may reduce the availability of vistas psychologically important especially in working spaces, and may increase the need for artificial electric lighting; nevertheless, at times, direct sunlight can be disturbing, and the delicate balance among all these factors may change throughout the day and from season to season. Moreover, a glazed window transmits not only natural light, but also, in its frequent single-glazed form, a great amount of heat, while its controlled transmission of the solar spectrum is in general difficult to achieve. During a cold night, an uncoated glazed surface lets heat out; on the contrary, during a hot day, it lets solar energy in, increasing cooling loads. For modern buildings with well-insulated construction and high percentage of glass, thus, it becomes more and more important to find this narrow path between opening to the environment and protecting from its extremes. In addition, the general performance requirements of a window system can change with the location, the climatic region, the orientation and the type of building, the exterior obstructions and shading, the interior spatial arrangement, as well as the needs imposed by different visual tasks and individual occupant variable choices.

3.1.2 Pelli; Canary Wharf, London

For these reasons, specifying façade solutions for energy efficiency can be a very complex affair; there are many design and context variables that interact with each other, making selection and optimisation more difficult. All things considered, wherever fixed optical properties are built into the glazing design solution, there has to be some kind of compromise in performance over time. For example, if a building façade uses highly reflective glass to control cooling loads, on an overcast day the room will seem dull and electric lights will have to be turned on (3.1.2). A clearer glazing solution may admit more light but at a penalty of solar loads and glare. Even for a north-facing façade, the solution has not to be taken for granted; however, especially for east-, west-, and south-facing Contract ENK6-CT1999-SWIFT

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façades - combined with seasonal weather conditions - one should be aware of a huge dynamic range in incidental and environmental conditions. The conventional remedies to the problems of light intrusiveness and unwanted overheating, for a long time, have been recognised in architectural solutions such as external overhangs; but they, too, are fixed devices that work well at some times and not at others (3.1.3). Other solutions lie in manually controlled shading systems, such as roller shutters, venetian blinds, curtains, operable shades, drapes. Some of those may be effective and add to the aesthetics, but nobody can assure that occupants are going to effectively manage an operable façade; in fact, in working spaces, users generally tend to feel it’s not their job to optimise the use of the building, with the result that shading devices will often be kept totally closed, with the consequence that the window is permanently no longer transparent (3.1.4).

3.1.4 Piano; Beyeler Foundation, Basel

In addition, specific disadvantages of some external systems, as fragility to strong winds, low efficiency and maintenance of the mechanical parts decrease the number of useful design options. For the above explained reasons, the search for a better comfort and the optimisation of energy management in buildings has recently favoured the experimentation and the development of innovative dynamic and interactive devices for the transparent building envelope, able to automatically dim the amount of solar radiation entering the windows. Amongst those Holy Grails of the fenestration industry, smart “switchable” glazing such as Electrochromic and Gasochromic glazing, finally make an old visionary dream come true. The vision of a building skin with variable characteristics, in fact, had been already suggested by Mike Davies in his article A wall for all seasons in 1981, where he presented the idea of a multifunctional skin that could act as a nanometric absorber, radiator, reflector, filter, and transfer device (3.1.5): “What is needed is an environmental diode, a progressive thermal and spectral switching device, a dynamic interactive multi-capability processor acting as a building skin. The diode is logically based on the remarkable physical properties of glass, but will have to incorporate a greater range of thermal and visual adaptive performance capabilities in one polyvalent product. This environmental diode, a polyvalent wall as the envelope of a building, will remove the distinction between solid and 28 transparent” . The turning point Davies was stressing out laid in recognising the enormous energy potential of the solar radiation striking the façades of buildings, both for thermal and daylight aspects; an ideal source of energy that does not pollute the environment and is present everywhere, in more 29 or less abundant quantities, at all time of the year .

3.1.5 Mike Davies’s Polyvalent Wall

So, the polyvalent wall “will dynamically regulate energy flows in either direction depending upon external and internal conditions, monitor and control light levels and constant ratios as necessary at all points in the envelope. [...] It is a dynamic performance element, which responds to continuously changing environmental conditions. [...] A “window” with those properties would have significant effects on architecture. We would be in possession of the first dynamically adaptive building material of a 28 large range of possibilities and properties” . So, architecturally speaking, the façade would take on a chameleon-like character: “The polyvalent wall is thus a chameleon skin adapting itself to 28 provide best possible interior conditions” . This comparison is not hazardous, since the chameleon, thanks to hormones that affect special pigment-bearing cells in its skin, is able to Contract ENK6-CT1999-SWIFT

3.1.6 A “switchable” chameleon?

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change its body colour in response to emotions (fear) or to react to light, temperature, and other environmental changes, becoming, for example, darker to absorb solar radiation and, thus, to get warm quickly, or assuming a clearer colouring, when external temperature raises up. Following this speculative proposition, the building skin, thanks to the recent advances in technologies already mentioned, can nowadays be able to evolve conceptually into an envelope with the ability to switch between transparent and partially opaque, modify its tint, and vary its optical properties (3.1.6). However, before getting on with this issue, we must say that buildings have been constructed and occupied for millennia without the need for the introduction of a variable behaviour; so, it can reasonably be asked why these concepts should be so relevant now.

3.1.7 The Earth, our ultimate house

The case for the “dynamic switchable envelope”, in fact, lies above all in the increasingly sophisticated requirements for energy efficiency and comfort, which have accompanied the development of complex building forms and contents in their more recent productions. One of the primary functions of buildings is to protect its inhabitants from the extremes of climate, and, as such, they must act as moderators in order to produce internal conditions that vary only within bounds contained into comfortable limits for the occupants. Recently, then, this moderation action has been further complicated by the fact that buildings themselves incorporate systems that introduce (thermal and energetic) loads, and thus contribute to the environmental equations 30 that determine internal conditions . On the other hand, it is just the incapacity of the passive building to provide comfortable conditions that leads to the expensive installation of those building technology systems - although, we must say, often an “improper” design can be accounted for increasing the problem determining enormous energy consumption for heating, cooling, lighting or ventilation, with the consequent depletion of traditional energy resources (fossil fuels) and the increasing environmental pollution caused by the emissions of CO2 and other greenhouse gases. As a consequence, it is easily understandable the reason why, above all in today’s extensively glazed and traditionally fully air-conditioned office buildings, a switchable façade, incorporating devices such as electrochromic and gasochromic glazing, could have both dramatic ecological as well as economical consequences (it is, by the way, significant the fact that the two terms, eco-nomy and eco-logy, have the same Greek root, oikos, that means house, residence, 3.1.7). Switchable dynamic glazing provide a means to adapt the building to specific needs varying with time and weather conditions. By continuously adapting to changing light and weather conditions, a dynamic building skin can assure adequate levels of illumination inside the building and sufficient solar protection against overheating, thus reducing the primary energy consumption of the building and creating a pleasant environment for the people inside (3.1.8). This helps globally to reduce the global greenhouse effect by limiting emissions, and locally to keep the investment and operational cost of building technology as low as possible. We must consider, in fact, that buildings now account for nearly half of all the energy consumption across most of the developed world, and that the energy budget related to them is burdened not only by heat losses, but, above all, by the energy needed for ventilation, cooling and lighting of 29 inhabited spaces . Contract ENK6-CT1999-SWIFT

3.1.8 Flabeg EC Façade, Dresden

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Moreover, the use of a façade incorporating switchable windows in combination with internal protection systems can provide benefits such as improved occupant comfort and perhaps performance and productivity providing a balance between the amount of solar radiation let in the room and the disturbance given by glare and contrast - while always maintaining an unrestricted visibility and transparency to the outside. Finally, this innovating glazing technology will allow permanent and undisturbed interaction between the occupants and the external environment, thus creating, as we are going to show below, challenging tools for the architects and designers of today and tomorrow.


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Application criteria: control strategies and design considerations

We are living a time of innovation (3.2.1). New products for the building envelope are dedicated to improve comfort, appearance and the energy performance of buildings. Keywords are: solar control, daylighting, thermal performances. The emerging concept of the window is becoming more a multi-functional 31 interactive “agent” rather than simply a static piece of coated glass . A traditionally passive building component has been transformed by switchable glazing into a dynamic device able to react and participate in building integration activities, with the consequences they may impose in terms of human well-being and performance; for this reason, the application and integration of those innovative devices requires a fundamental change in our conception of design and functions of the 32 building envelope . With the innovation in technology comes the opportunity for more comfort, and better productivity (that influence building economics far more than does energy consumption alone), but only if the integration and control strategy is well adapted to the needs of the users. Research should provide powerful design tools to help get the most out of those promising devices, so it is of fundamental importance to understand how they should be integrated in architecture in relation to all the other components that can help create liveable and comfortable conditions inside inhabited spaces. In architecture, sometimes, design decisions can be fairly simple; but the design of a building façade, as previously highlighted, involves a complex set of factors. Heating, cooling, and lighting considerations alone send calculations off in many different directions. Then there’s thermal comfort, visual comfort, and performance issues; and the proposed solution has to be sensitive to climate, building orientation, occupant activity (computeroriented vs. paper tasks) and so on.

3.2.1 Piano; G.Pompidou Centre, Paris

However, if buildings are designed for people and not only for aesthetic or profit reasons, they must always provide the right environment for the wellbeing of the occupants and their activities; the value of a building, in fact, relies not only upon its rentable net area but also upon the quality of the space it envelopes (3.2.2). We have to strike a balance between the quantitative considerations (How much light do we need for this space?) and the qualitative part (What will the space look and feel like?). The following strategies and design considerations include comments on several themes which are relevant in terms of required performance, and principally: • Dynamic control of transmitted solar flux so as to reduce cooling loads. • Control of direct and indirect glare and reflections. • Improvement of the light distribution in occupied spaces. • Design of fenestration devices as part of an integrated building system. • Provision of lighting systems that support changing occupant needs and enhance health, comfort, satisfaction, performance, and energy savings. • Provision of decision support tools that can assist architects, designers, engineers and owners in evaluating and choosing amongst all the different 33 available options . Control Strategies Contract ENK6-CT1999-SWIFT

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The need for variability has already been demonstrated at the beginning of this chapter; the notion is not new (3.2.3), nor is it necessary complex. In architectural design, the openings for views and light have long been considered as weak points in terms of energy transmittance, and, despite the recent enormous increases in glazing performance, including the development of low-Emissivity coatings, this problem still remains. Short-wavelength solar radiation is able to pass through glass, and is not always welcome; what variability may offer is the chance to control some characteristic of the transparent surfaces, modifying the performances carried out by the devices. The use of variation in the building skin, besides, is already well ascertained, since the venetian blind and fabric curtains, for instance, 30 represent two of the simplest - and, at the same time, oldest - examples . Those shading systems can give radiation and at the same time behind the glazing, they are a functional and variable nature contradictory requirements.

protection against the intrusion of solar provide privacy. Nevertheless, if used potential heat collector, so the multiof such devices poses problems of

The lack of information on the distribution of operating conditions in the 30 future is yet another difficulty . For example, the wishes of the user at one given moment may contradict the needs of the building for the next hours; a solar gain in the morning may contribute to peak loads later in the afternoon. During winter months, this solar gain may be welcome to reduce heating loads, but it is useful only if it can be admitted in a manner 3.2.3 Rietveld; Schroeder Haus, Utrecht 34 that does not contribute to thermal discomfort and glare . In addition, we must consider that many built spaces are not used for a great part of their time. In general, residential buildings remain at least partially unoccupied during working hours, while commercial buildings are not inhabited at night; these two time periods have very different climatic and environmental characteristics and needs. The other major variation imposed on buildings comes from the constantly changing habits of users and accommodation strategies, while - further more - the way that people interact with the architectural envelope is another constant source for differentiation. As a consequence, the idea of introducing dynamism in the external cladding of a building to respond to these changes, rather than relying on energy consuming building services, 31 can offer tremendous advantages (3.2.4). The concept of switchable glazing aims to respond to this complexity, with solar-optical properties that change in response to variations of external and internal factors. As already stated, their use in commercial buildings can reduce the peak-electricity demand and the cooling, lighting, and total electricity consumption associated with windows in many ways (in comparison with conventional fenestration technologies). The darkening of the glass can protect the interior from overheating when the solar radiation increases in the course of the day, and minimise the cooling load as well as reducing both glare and reflection on computer screens. Although a switchable glazing cannot protect from direct glare from the sun, it can be effective for mostly all other external glare sources like bright clouds, bright façades or other dazzling surfaces nearby, meaning that its use can contribute to eliminate the need of additional window fittings such as external blinds or drapes for solar control and glare reduction. However, unlike the all-or-nothing solution of exterior blinds, even in its most coloured state, a switchable window always permit unobstructed view to the outside. Its maximum benefit can be obtained when the glazing is used in 3.2.4 Nouvel; IMA, Paris conjunction nd in str tegic integr tion with dimm ble electric lighting Contract ENK6-CT1999-SWIFT

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conjunction and in strategic integration with dimmable electric lighting control. In fact, since switchable glazing can be lighter when there is little sunshine, the need for artificial lighting can be consequently reduced. They further have the possibility to be linked to the building's management 35 system (BMS) and to adjust continuously to changing exterior environmental conditions, occupant preferences and utility needs. In principle, each pane may be adjusted individually, according to the parameters specified by the user; this may be done in a manual interaction, probably, with central control systems. However, it seems to be more practical to control several windows together in groups, thereby synchronising the individual controls and their degree of colouring. Switching may take place simultaneously in a room, in a complete façade or for the whole building. The choice of grouping for a specific building project has to consider the homogeneity of room specifications, the load variations and user acceptance.

3.2.5 A Flabeg EC Controller

In fact, within the scope of an individual building climate concept, integration of the switchable windows into the building control system allows the power saving potential to be utilised to the full. By doing that, an optimum level of energy savings and efficiency in the building's energy balance can be achieved, thus providing the lowest energy usage at the most comfortable temperature (3.2.5). For optimum power utilisation, the building control system should always aim to reach the state that achieves the lowest energy consumption while maintaining visual and thermal comfort. It is, however, good practice to specify tolerance ranges, so as to prevent the system from reacting to changes of short duration, caused for example by passing clouds.


The control logic for a switchable façade system can include a complex set of strategies: solar gain control with a view to optimised energy saving, glare control, maintaining desired illuminance levels, and view control. Whether the automated control sets preferences to the solar control by responding to the indoor temperature, to daylight requirements by responding to desk illumination, or to the visual comfort by responding to glare, has to be decided in any case. The switchable façades allow the exploitation of these options for a simultaneous optimisation of comfort and of energy consumption. However, the identification of the control strategy better suited to a specific case is obviously one of the tasks that has to be clarified already in the planning process of a building project, even prior to the implementation of the switchable glazing system. In general, it is believed that in warmer climates (cooling loads driven), solar control is much more important than lighting control. For example, in a cooling-dominated situation, control algorithms based on daylight illuminance to reduce electric lighting and increase the use of natural light can result in high energy consumption levels due to the use of air conditioning systems to prevent overheating; controls related to space cooling can yield better performances through solar heat gain reduction. In heating-dominated geographic locations, on the contrary, the best performance can be assured by a control strategy that leaves the switchable glazing in its fully-bleached position during the heating season; however, this may result in glare and visual comfort problems for occupants in much the same way as conventional glazing (3.2.6). An appropriate solution would be to use internal, light-scattering blinds to combat the glare, without changing the solar gain significantly. Contract ENK6-CT1999-SWIFT

3.2.7 Coenen; NAI, Rotterdam

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Naturally, one might argue that a well-managed exterior blind/shades system, directly adjusted by occupants, could achieve similar benefits. However, when manual control is the only option, field experience suggests that the energy-saving potential is rarely achieved in practice, since users may react to acute visual discomfort by pulling down a blind, but they will seldom make the gradual changes needed to optimise energy saving (3.2.7). Given the range of user activities that can occur in a space, nevertheless, it is always also important, from a psychological point of view, to provide occupants with at least a partial over-ride capability and the facility for local fine-tuning, so that people do not feel that the system is out of their control, nor become dissatisfied because of a highly automated environment.


A BMS, in fact, cannot always fully accommodate user preferences for the illumination of a given task type, position, and field of view as well as addressing conditions and concerns including glare, direct sun, view, brightness, colour rendition, and a multitude of others. We may envisage, consequently, a user over-ride with a remote controller at any time, but with a central system that is able to return to its default settings when the occupant is absent (occupancy sensors) or after a given period of time. Probably, the user control would not be used very often, and would not thus greatly affect the overall energy efficiency strategy where much of the hour-to-hour adjustment is left to a properly designed and calibrated automated system. However, it is an essential feature to 33 avoid annoyances and complaints (3.2.8). In addition, since switching occurs in a controlled and slow manner so as to provide a uniform appearance over the entire process, another aspect can be the feedback by the controller to the occupant, so that the user can determine whether the glazing is at rest or rather if it is in the process of switching to another state. For all of the aforementioned reasons, it is fundamental that a "smart" controller be able to optimise under widely differing conditions and “adapt” to contextual situations, where for example, the desires for view, energy savings, and visibility may conflict with each other. In fact, since the control of the windows, of the lighting levels in the room and of the heating and cooling equipment are logically dependent on each other, an ideal controller should manage all together: switchable glazing, glare protection devices and artificial dimming electric lighting. Computer simulations and façade tests carried out within the SWIFT project suggest that, in general, the most appropriate control strategy should preferably adjust the switchable glazing according to (a combination of) the solar radiation and the indoor temperature levels. We can basically distinguish between a heating and a cooling “mode”. During heating-dominated periods (winter), the switchable modules are generally kept in their bleached (transparent) state by the controller. The control system triggers the setpoint of the glazing just to protect from glare effects from indirect sources, while the glare protection from direct sources (sun) is provided by the use of venetian blinds (horizontal stripes for southern and northern orientations, vertical stripes for eastern and western). Since the blinds are mounted inside the glazing, it means that most of the solar radiation penetrating the façade can be translated into solar gains, even if the blinds are kept down, thus contributing to reduce the energy required for heating the spaces. During cooling-dominated periods (summer, but also spring and autumn in Contract ENK6-CT1999-SWIFT

3.2.9 SWIFT EC test room at ENEA

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most commercial buildings because of internal loads) the façade is coloured by the management systems when the optimised setpoint (i.e. solar radiation on the façade and/or indoor temperature) is reached, so as to optimise the needs for lighting and cooling (3.2.9). This means that, sometimes, the façade could be switched to a coloured state and the electric light could be turned on, although the available daylight would have been sufficient for the bleached state but is not for the coloured; however, in that case, the cooling energy required to prevent overheating would have been much higher than the energy demanded for artificial lighting. The user is always endowed with the capacity of over-riding the central control system and temporarily change the state of the glazing into a more transparent (or coloured) level according to its preferences and/or visual needs (glare from indirect sources, contrast, temporary need for lower or higher illumination). Nevertheless, after a predefined period of time the automatic control system takes over the control again and change back the setting of the glazing to the previous one. For instance, a possible scenario of how a switchable device may work in an office setting could be the following: a thermosensor (for a control strategy that is optimised for cooling-dominated situations) can measure the temperature inside the room and compare it to a specified level. If the incoming solar energy is insufficient, the glazing is switched to its clear state and the artificial lighting is adjusted to ensure that the minimum level required is reached. If glare from direct sources is a problem, it is eliminated with the internal blind.

3.2.10 SWIFT GC glazing at ISE

As the internal temperature increases, due to major solar gain triggered by an increase in daylight penetration, the glazing switches to its coloured state and the electric lights are consequently appropriately adjusted. Solar gains are thus minimised and cooling energy is needed only under extreme situations (3.2.10). When there is no longer direct sunlight, the glazing is bleached again. As the day darkens, the electric light brighten to the extent that is needed. As a conclusion, in all practicality both the user and an automated system should be able to control switchable façades in order to improve the overall performance of the system and the occupant satisfaction. For public (lobbies, glazed hallways, cafeterias, offices, etc.) or open-plan shared spaces, some lack of autonomy regarding the window system can be acceptable to occupants, and in this case, multi-pane control would allow more flexible management than single-operating windows. For example, in a composite façade unit, an automatic controller could activate the upper windows separately from the lower windows.


On the contrary, for private installations, it is advisable that manual controllers be coupled to an automated system, and be mounted on walls adjacent to windows. As always, any general rule should be adapted 32 according to the specific requirements of the case . Design Considerations In order to reach the benefits mentioned above, some considerations must now be given to the potential use of electrochromic and gasochromic glazing, depending upon aesthetic issues, visual and thermal comfort for the user, orientation and climatic conditions. Switchable windows can indeed provide unmitigated transparent views and a level of dynamic illumination control never before seen in building Contract ENK6-CT1999-SWIFT

3.2.12 EC (top) and GC samples

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glazing materials. Naturally, they may not be able to fulfil both energyefficiency, thermal and visual comfort objectives in all circumstances and under any conditions. However, following some general rules of design and correct integration can contribute to broaden the applicability of these devices in architecture. 31 32 33 34

For this reason, we can draw on recent publications on the subject 38 40 43 , supported by the field experience directly conducted by the author within the SWIFT project, to identify how switchable devices can be used appropriately in occupied buildings (3.2.11). In the following design considerations, the analysis will focus its attention first on the appearance of those innovative devices; then, we will move on to considerations about daylight control, respectively with the device in fully-coloured and fully-bleached state, and then to glare effects, view and privacy and thermal performance; after that, we will shift our attention to switching speed and to cycling and, finally, we will address the problems related to costs/benefits.

3.2.13 SWIFT EC window at ENEA

Appearance In general, regarding aesthetic characteristics, the chromogenic windows reported here both switch from a clear state to a deep Prussian blue, even if with a slight difference in coloration between electrochromic and gasochromic (3.2.12). For the application in fenestration systems, the coatings present excellent optical clarity and a good uniformity of coloration. To all outward appearance, in substance, the switchable windows look exactly like conventional solar-control windows with the exception that one can change their intensity of coloration.

3.2.14 SWIFT GC glazing at ISE

Transitional appearance (during switching) can be considered to be less important than a permanent non-uniformity, even if good synchronisation (or colour matching) between a group of windows during and after switching is rather important. The degree of optical homogeneity reached by industrial products is anyway high and probably sufficient for all applications, not presenting pin holes, inactive areas, or other coating aberrations. Concerning the possible alteration of the luminous environment and the differences in colour perception due to the switching of the glazing, user 36 37 assessment studies have highlighted that the majority of the users may actually perceive a distortion in their visual external environment, but are not necessarily bothered by that. In fact, although the colour of the view outside can sometime seem rather 36 “unnatural”, it does not have to be necessarily unpleasant (3.2.13). Nevertheless, it is interesting noting that, during tests and monitoring, some users did not perceive at all an alteration in the outdoor environment - even when the window was in the fully coloured state - unless when asked about. This could mean that not only the tint of the glazing in its fully-coloured state is, in general, quite well accepted by test-users, but, in addition, that slow automatic adjustments in the transmission level of the 37 glazing will probably be unnoticed and therefore not bother users . Regarding the potential alteration of the internal luminous environment, it must be considered that the strong blue hue of the glazing when fullycoloured may, in some case, affect brightness and colour perception, posing some problems for tasks that require accurate colour rendition, as, for example, in retail and medical buildings, food markets, museums, etc. On the other hand, the level of alteration may broadly change according to the tint of the original colour, the artificial lighting and the type of glazing Contract ENK6-CT1999-SWIFT

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(electrochromic or gasochromic). Different backgrounds, for example, may entail significant effects on the perceived colour of the glazing, although windows are all switched at the same state (3.2.14).


Occupants will also be likely to notice the strong blue colour if bleached and coloured devices are juxtaposed in the same window wall, creating a contrast effect that may influence their perception of brightness in the space. Windows switched to different transmission levels within the same window wall would make these effects more apparent (3.2.15). Subjective human factor studies are further being performed to determine preferences for transmission range, direct sun control, and switching speeds for different tasks, all the more reason why thorough window designs and control strategies should be considered so as to optimise the performance of switchable glazing in buildings. 3.2.16 SWIFT EC test room at TU/e

Daylight, Glare, View and Privacy The performances achieved by switchable glazing systems may vary broadly according to the particular task accomplished in the space that they envelope. For reading, writing, and object-manipulation tasks, in fact, the most significant and immediately evident advantage guaranteed by a switchable window is the simultaneous provision of views and the control of interior illuminance. A controlled intensity of direct solar illumination, in fact, can be surely adapted to “traditional” working environments, while direct and indirect glare or reflections can usually be avoided by changing the position of the task or the eye. Throughout the day, then, an unobstructed view can give benefits providing relaxation and ocular relief, and a visual link with the outdoors. With a computer-based activity, on the contrary, the requirements of visual comfort are more stringent due to the self-illumination of the task. The intensity of light incident on the PC screen and on opposing room surfaces must be carefully controlled so as to prevent disturbances on the image and direct reflections. To avoid eye fatigue and glare, background 38 luminance within the occupant’s field of view must also be well managed .


Concerning the visual and solar transmittance levels of a switchable window, a very low transmittance in its fully-coloured state may present great advantages because visual comfort can be improved, while, simultaneously, solar gains can be reduced to a level that expensive external shading is not any more required. In general, switchable glazing alone cannot simultaneously provide control for direct light, solar protection and assure an optimal daylight level for every task, view and solar angles. If a switchable window should act as both the protector and the admissor of light, it is difficult to find an optimal balance between energy-efficiency and direct solar control, since, satisfying one criterion would be detrimental to the other (3.2.16). 38

Besides, preferences in general change from occupant to occupant . The main benefit given by the use of a switchable glazing, compared to a “traditional” static window system equipped with external shading devices for solar control, is however the possibility of having an unrestricted view through most of the day, which is the primary role of most windows (3.2.17). A low visible transmittance, in addition, can reduce the percentage of time in which high window brightness can cause glare. Nevertheless, since a coating with sufficiently high transmittance to retain visibility in its fullycoloured state is fundamentally unable to attenuate glare from directly incident sunlight, internal blinds will still be required for direct glare control, though the frequency of their use may be reduced appreciably. Concerning the fully-bleached (clear) state, a high visible and solar transmission level can help to decrease the energy consumption for Contract ENK6-CT1999-SWIFT

3.2. 18 SWIFT EC test room at TU/e

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heating (solar gains) and artificial lighting, improve contact with the outside environment, widen the installation of switchable windows even to buildings where daylight availability is basically poor, and increase interior illuminance level and room brightness. If we compare a switchable glazed unit to a static glazed pane of higher transmittance, the artificial lighting energy required to maintain a given level of illuminance in the room is obviously greater. This is because the static glazing always transmits as much or more daylight as the dynamic one in its clear state, which, in addition, could often be switched to control direct sunlight, thus requiring some added artificial lighting sources. Overall, however, the higher-transmittance static glass may result in more glare problems and cause major cooling loads. In an occupied space, in addition, people would add and often pull down the blinds for visual and solar control, in this way destroying the apparent advantage given by the traditional static transparent opening.

3.2.19 Light level at sunset

Glare caused by direct sun is almost always a comfort problem. Uncomfortable occupants are likely to be less productive, close their window awnings and augment their use of artificial lighting systems (3.2.18). 39 Good shading thus means minimal complaints for the occupants . As some studies show that occupants are more tolerant of glare from windows provided that the light source is accompanied by a view, there is hope that switchable glazing would be sufficient to reduce glare to accepted levels in most situations. Those studies suggest that lighting fluctuations coming from a natural source are generally quite well accepted, while people tend to find 40 changes in the artificial lighting environment rather disturbing . Controlling the intensity of direct sun, anyway, determines in general a rather unique situation for visual comfort, as many variables have to be considered at the same time: size, position, uniformity and intensity of openings and luminous sources in the field of view, type of visual task, etc. Moreover, it must be considered that the subjective response to a lighting environment is a complex issue, as already highlighted, and impressions of glare discomfort are influenced also by other visual sensations, many psychological variables, testing conditions and individual variation. The net effect of these factors on the judgement process can lead to a systematic error resulting in variability of the ratings, which may not 41 correlate to the variability in the stimuli being rated . Low solar positions exacerbate direct sun effects for south-facing windows in winter; north-facing openings, on the other hand, receive low direct sun less frequently during mostly unoccupied periods (early morning and late afternoon, in summer months), while east- and west-facing windows will experience this problem throughout the year. If the sun (or its reflection) is in the field of view, its luminance can range 2 from several million cd/m - when it is near the horizon - to over a billion 2 cd/m - when in its highest position - seriously decreasing the visibility of other surrounding objects, and thus augmenting the sensation of pain or annoyance that is created by a high or non-uniform brightness (3.2.19). In addition, even where there is no direct sun discomfort glare can occur if the glazing - or a shading device - is not able to control the bright sky luminance. The average luminance of the sky, in fact, can range from 2 2 2.000 cd/m for overcast skies to 8.000 cd/m for clear skies, while cloud 2 luminance can reach 30.000 cd/m . As a consequence, for these conditions, blocking direct and indirect glare with a protection device is fundamental to allow visual comfort.



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Switchable glazing can decrease the frequency of discomfort glare due to window brightness compared to static glazing; as already said, it cannot fully avoid glare from direct sources, as when the sun is in the field of view, but this reduction may be sufficiently effective for diffuse sky conditions with high luminance. Under sunny or partly cloudy conditions and with relatively slow switching speed (as we have at the moment), instantly deployed interior shading devices is an ideal response to this need. 36 37

Nevertheless, as from the results of user assessments , although the necessity of using internal blinds to protect against direct glare sources, occupants can be significantly bothered by not being able to see through the windows. Opaque shading systems such as venetian blinds at a cut-off angle can satisfy both of these requirements; this solution is generally preferred to the curtain blind. With venetian blinds, in fact, the modes of operation include tilt angle and retraction (up, down), which satisfies the criteria needed for solar heat gain control, daylight distribution and, partially, view. With roller shades, on the contrary, one controls the degree of shade retraction, so that the view and the daylight are also automatically blocked when glare control is needed. Commercially available products now offer several methods of control; simple manually operated keypads have tilt open/close as well as up/down options for venetian blinds. It must be considered that automated shading systems have a higher initial cost and an added maintenance cost compared to other shading schemes; however, the operation should be more reliable than with manually 31 operated systems .


Careful calculation of expected energy savings are needed to determine cost-effectiveness for this approach. More detailed discussion of these devices is, however, beyond the scope of this paper. Concerning glare and reflection effects on PC screens, direct illumination can decrease the visibility of VDT tasks by reducing contrast or washing out the screen image. In general, old cathode screens are considered to be more susceptible to those problems, while newer display technologies, such as liquid-crystal screens with anti-reflection coatings, can be even viewed under some direct sun conditions. To fully avoid those effects, again, shading devices are needed to block direct glare sources (3.2.20). Switchable glazing can contribute to minimise the need for those additional protections, since solar control and glare reduction should be sufficient nearly at all times, leading to better views and daylight provision. However, for computer tasks, replacement of older screens with newer LCD displays or improved anti-reflection coatings could further mitigate this problem. Regarding view and privacy, if a low transmittance state is used to control direct sunlight penetration, the visibility of external objects through the glazing may be possibly reduced in some cases, since contrast sensitivity (the capacity to distinguish differences in luminance) can be decreased. To ensure visual privacy during the day for most subjects and tasks, a low transmission level (as the one we have at our disposal now) can be considered to be sufficient to avoid inspection from outside, reducing the contrast of objects viewed through the window (3.2.21). At night, or when the subject is directly illuminated by a source of light, however, a lower visible transmission is needed to ensure privacy than can be offered by non-scattering, chromogenic glazing. The condition of privacy perceived by the occupant is probably a more 3.2.22 The Flabeg E-Control® spectrum i t t th h l i t tf li i Contract ENK6-CT1999-SWIFT

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important, though more complex, issue; occupants may not feel in privacy, if they fear themselves being watched. For applications where privacy is a fundamental aspect, therefore, opaque shades or other architectural devices will always be advisable. Thermal performance Concerning thermal performance, again, balancing between visual and solar energy transmittance depends on many factors; in fact, to avoid or foster overheating caused by direct and diffuse solar irradiation, alternate control strategies and/or shades are advisable. In all practicality, for convective and conductive heat transfer, the EC and GC devices, provided in double or triple glazed units (DGU and TGU) are surely able to assure a satisfactory U-value in any condition (U = 0.9-1.6 2 W/m K). However, the perception of comfort by a person depends not only on simple air temperature, but also on the temperature of the surrounding surfaces; the ‘mean radiant temperature’, actually, exerts a large effect when the person is close to the window, both in winter and summer situations, because of the radiative exchanges between a hot (or cold) surface and the occupant. For this reason, electrochromic and gasochromic coatings are always used in insulating units, keeping the switchable layer on the external pane of the window. Solar gains through the switchable windows in fact are reduced by a factor of approximately 3, when changing from the bleached to the coloured state (3.2.22). The switchable glazing rejects heat by absorption, rather than reflection, and so the outer pane of the DGU or TGU can get quite hot when directly irradiated; however, the glazing unit ensures that the heat is not transmitted to the inside, thus keeping the temperature of the interior pane at a significantly lower rate, even in cooling-dominated conditions, as during summer months. By contrast, in winter, the inner surface temperature of the glazing in its fully-bleached state may be significantly higher than that of the external pane. In addition, low-Emissivity coatings, gas fillings inside the unit cavity or proper blinds or shading devices on inner glazing surface will further reduce the radiative effect, providing interior glass surface temperatures closer to interior air rates, and improving thermal comfort in the vicinity of 33 the window .

3.2.23 A 20 min. SWIFT EC sequence

On the other hand, positioning the switchable pane on the outside of the unit can be functional from another point of view, as it could help accommodate wiring through the framing, in such a way that defective frames can be replaced form the outside (similar to most curtain wall applications). Switching speed In general, colouring and bleaching times are affected by environmental conditions (temperature) and glazing area. Switching speed can also vary with the number of cycles; typical times, for normal window size panes, are from 10 to 20 minutes. In theory, a hypothetical window presenting a fast switching speed (2 to 3 minutes) could be used to ensure visual comfort in buildings, particularly if used without exterior or interior shades, and in the case of personal control by the user. In fact, in this case, direct light sun control could be fairly immediate, if no other options for its management are available (e.g. reposition task or eye, or draw the shade). For example, if the switchable glazing was used by the occupant to avoid glare, as in the situation where the sun is intermittently obscured and revealed by transient clouds, a slow colouring of the glazing might reach Contract ENK6-CT1999-SWIFT

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its limit after visual discomfort has been alleviated, especially when the deeper coloration of the window was chosen. The resulting user annoyance could even lead to a reduction in task performance. However, for these fast adaptations to environmental conditions the current technology is too slow (3.2.23); the question remains whether the users would not be bothered by those sudden change in illumination level. In fact, instantaneous switching can also have undesirable side effects, such as distraction or unexpected alteration of the diurnal connection to the outdoors. Moreover, as we have explained above, variations in lighting intensity can provide information about the weather conditions, the time of the day, the seasons, and result in positive health effects, while a switchable glazing controlled to always maintain the same interior illuminance could be detrimental to interior light level variations, resulting in monotonous visual conditions. It must also be considered that too rapid switching can thermally shock the glass causing stress and possible shattering. The slower switching speed that is achieved in practice by the current generation of switchable glazing is certainly sufficient to allow control according to thermal comfort (indoor temperature), which is generally also a good energy-saving strategy. One more time, the general control strategy has to be optimised according to specific requirements, and, thus, again, interior shades are recommended to decouple the aspects of visual and thermal comfort. Since switching speed is influenced by various factors, as above explained, a multi-pane controller between windows of various dimensions has to asynchronously consider those differences; use of smarter algorithms that have a memory of site conditions is recommended to improve comfort and to adapt to pre-set situations.

3.2.24 SWIFT test box at ISE

Cycling Cycling, or repeated colouring and bleaching, defines the sustained performance of a switchable glazing over its expected life of 20-30 years. Performance goals for typical building applications may vary from 8.000 to 25.000 cycles, assuming an average of one to three cycles per day. In fact, it is possible to preview no cycling at all during an overcast winter day (device always fully-bleached), two-three cycles on a cloudy day, and one full cycle on clear winter days, in case the strategy has been optimised both for energy-efficiency and direct sun control. Of course, those consideration may vary considerably according to building and site parameters such as glazing area, illuminance set-point, weather, window orientation or other control strategies (glare, temperature, etc.). On the other hand, the number of cycles per day may also increase appreciably if the user is provided with the possibility to over-ride the automatic management system (for example, to improve visibility). The use of tempered glass, as is common for static solar-control glazing, is recommended to avoid breakage. A minimum change in transmission limits over the life of the device is required to ensure sustained performance over the life of the window. In addition, there may be restrictions in the change of appearance; as the devices have in their various transmittance state a different defined tonality, the initial colour should not be subjected to changes exceeding a certain range (e.g. to allow replacement of a single non-functioning module in a large glazed façade) (3.2.24).


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Costs/Benefits Switchable devices are currently surely more expensive than traditional fenestration products, though they will probably decline in cost as the technology and the manufacturing processes mature, and adequate 38 market share is gained . Nevertheless, it is important to caution against direct cost comparisons, because the use of switchable glazing means generally turning the window into an appliance with a whole new set of features and benefits for the building occupants, that can transform the building character and even reduce annual operations and maintenance costs. Thus, inclusion of hardto-quantify factors such as comfort, productivity, tenant retention and building amenity should also be included in the analysis.

3.2.25 Purely financial estimates?

A correct use of a switchable glazing can result in improved energy efficiency and reduced energy demand, with the environmental benefits of reduced consumption of fuels in power plants, reduced emissions from existing power plants, and reduced need for construction of new power plants. Moreover, a reduction of heating and cooling loads means less space required for equipment, smaller mechanical rooms, smaller shafts and less ceiling plenum height, with the consequent economic profits for the builder. Of course, the benefits in terms of energy saving and peak load reduction are dependent very much on the reference technology. The interest of switchable façades is that they may be as efficient as expensive external shading on top of low-E coated glazing, but have additional advantages as visibility and non-mechanical operation. Therefore, instead of purely financial estimates, other benefits for the client should be considered, such as increased daylighting with reduced glare or solar gain and increased access to views that do not need to be obstructed 42 or covered to maintain thermal and visual comfort (3.2.25). This all means paying attention to “human” operating costs that, mostly in working environments, generally translate into measurable consequences on satisfaction and performance. Business managers increasingly recognise that their most important financial asset is not the buildings they own, but rather the people who occupy them. Building design parameters that influence worker satisfaction are very important economic considerations too, taking in due account that an occupant’s comfort and productivity may very often be far more 43 expensive than the energy he consumes .


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Architectural Potential of Switchable Glazing

According to the control strategies and the design considerations described above, the switchable façade technology seems to be very well suited for climates with, above all, overheating problems and thus prevailing cooling needs (Mediterranean, Tropical, Sub-Tropical), or in situations where minimising solar heat gain, without affecting a direct view to the outside, is the major issue to confront. In northern climates (Central-Northern Europe, Continental climates), however, these concepts may be applicable too, mainly during summer and transitional months. In these geographic conditions, in fact, cooling needs connected to excessive solar gains can often be a necessity due to longer days and lower sun elevation than in southern climates where, in addition, cooling loads result basically from higher environmental temperatures and cannot be changed much by switching the glazing.

3.3.1 Demo-building simulations

For problems related to negative daylight conditions such as direct or indirect glare or light contrast, the use of switchable glazing may surely be helpful in almost any situation; nevertheless, as said before, additional internal shading devices (venetian blinds) may be needed for direct sun control (throughout the year, in the morning and afternoon for eastern and western orientations; in winter, at noon for southern orientations). For south-facing windows, simple external overhangs could prevent direct solar radiation during summer months, so as to avoid direct glare and overheating, because of high sun positions. In winter, a switchable glazing can guarantee control upon direct and diffuse radiation, providing natural solar gain when in its fully-bleached state. Of course, energy and demand savings for northern orientation applications are modest, but there could be a significant benefit even in these cases, in terms of glare and contrast control. Concerning the integration of switchable glazing with all the other components inside the building, and in particular with artificial lighting systems, we may say that often a good daylighting design fails to achieve the energy savings expected, due to problems in the lighting systems. These failures may comprise installation, wrong product selection (sensors and electronics) and architectural design problems (placement). Hence, the system not only has to maintain the desired illuminance levels under a wide variety of conditions, but the overall lighting design must create a visually interesting space, as the illuminance levels from artificial lighting are dimmed according to daylight (or transmission level) changes. As glazing systems become switchable and dynamic, electric lighting controls must then encompass this added performance complexity, being linked to the building energy management system too. The efficiency of a daylighting strategy is supported by a responsive artificial lighting system, endowed with the ability to dim or even deactivate itself (from 100% to 0%) according to occupancy sensors or sensed internal lighting levels. In any case, however, the glazing design must be driven by interior results as much as exterior appearance. Form, siting, and building skin decisions strongly influence daylighting performance, cooling loads, and occupant comfort. The best lighting and mechanical system can not solve architectural errors with respect to perimeter zone comfort; window and room design must always provide for both, visual and thermal comfort. Occupant satisfaction will depend on the match between environment and task needs, so it is important to know the intended use of the space lre dy during the design st ge Contract ENK6-CT1999-SWIFT

3.3.2 Details - Switching simulations

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already during the design stage. User response and acceptance of switchable windows has to be the target, since annoyed occupants tend to disable poorly designed control systems. In terms of user assessment of the SWIFT technology, bio36 37 feedbacks have highlighted that in general people easily accept a partially coloured fenestration, if a clear view to the outside is assured. It is, nevertheless, important to always provide the user with the possibility of partially over-riding the central management system by the use of a manually operated control. From an aesthetic point of view, the use of switchable glazing is surely well suited for fully-glazed envelope solutions, and in particular for all the types of buildings generally labelled as “tertiary” (offices, services, schools, educatory, hospitals, etc.), though, if designed in a proper way, it may be useful, in terms of both comfort and energy saving, and also architecturally interesting, even for other “hole in the wall” applications.

3.3.3 Piano; KPN Building, Rotterdam

In a fully- or partially-glazed façade, switchable electrochromic and gasochromic glazing could provide, both on the inside and the outside of the building, continually changing patterns according to the variable setting of switchable modules, that can be interesting both from the general comfort and from the architectural point of view (3.3.1). Moreover, the use of frames with different sizes and shapes, maybe even arranged in variable combinations of patterns and colours, could realise interesting façade solutions with variable inside (and outside) lighting conditions, that could even foster the characterisation of different spaces and parts within the same building.

3.3.4 Toyo Ito; Multimedia Installation

So, we could imagine that, as the glazing changes gradually in response to external or internal stimuli and needs, there will be noticeable differences in colour and opacity between different areas of the façade(3.3.2). In order to understand the kind of aesthetic effect this conception of the building envelope as a “living entity” may give, we may refer, for example, at some experiments carried out in Europe (3.3.3) or Japan (3.3.4). In those experiences, the integration of mini lamps or ring-like neon, lit up by a computerised system according to different strategies (advertisement, news, or even the wind direction and velocity or the level of noise detected on the building site), make the building “react” to external stimuli, enriching its envelope with a kaleidoscopic effect in some occasions, or transforming it into a diaphanous transparent film in some others, thus converting intangible phenomena into architecture (3.3.5). In addition, we may even think that the use of a building cladding endowed with the capacity of varying its reactions and interactions with external light may also be intriguing in that it could alter the “weight” of a building, as for example, in high-rise towers, with the top floors left in a fully transparent state and the lower levels gradually coloured until the base, or vice-versa. From a thermal point of view, in the design of a glazed envelope, switchable devices may be useful both in single and double-skin solutions. If we think of a single-skin façade, it is well established that, in order to provide comfortable conditions inside enveloped spaces, it often has to be coupled with additional shading devices, placed outside or inside the glazed skin, or incorporated in the cavity between the glass panes. Obviously, the advantage of exterior solar control devices, in the form of fabric blinds or louvers, fixed or movable, is that the heat resulting from the re-radiation of the device itself remains on the outside of the building; a main disadvantage, however, is that those systems are continuously exposed to environmental agents, such as wind, solar radiation and rain, Contract ENK6-CT1999-SWIFT

3.3.5 An electrochromic shadow

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which eventually can give rise to significant costs for cleaning and regular maintenance (3.3.6). A switchable device, with its colouring layer placed on the outer pane of a double or triple glazing unit, may yield the same advantages in terms of solar-control capabilities, while always maintaining a continuous view to the outside and minimising the additional costs required for maintenance. The same could even be said for the single-skin solutions that include a solar control device integrated into the glazed unit; actually, in this case, the cost for cleaning may be lower, but the maintenance could sometimes even demand the complete substitution of the entire device. Regarding interior solar control devices, it is well established that those shading systems are useful mainly for daylight control but not for solar control, because, in this case, the re-radiated heat would remain inside the room (3.3.7). For this reason, those products could be even more useful if coupled with a switchable glazing system, where the latter may provide control of solar gains according to the chosen strategy, while the former is 29 responsible for avoiding glare or contrast problems .

3.3.6 Nouvel; Fondation Cartier, Paris

In double-skin façades, the possibility of incorporating a solar control device in the cavity between the two glazed skins, thus protecting it from the influences of weather and air pollution, naturally reduces cleaning and maintenance costs. However, the use of switchable devices may be useful and interesting even in this case. In fact, double-skin façades are generally designed to create a thermal buffer zone that can afford great advantages both in heating and in cooling-dominated conditions.

3.3.7 Perrault; Hotel Industriel, Paris

In winter, a double-skin façade may reduce heat losses, because the reduced speed of the air flow in the cavity - together with its increased temperature due to solar heating - can lower the rate of heat transfer, thus maintaining higher surface temperature on the inside of the glass, and, consequently, a better utilisation of the spaces closer to the windows. In summer, the heating of the air inside the cavity creates a natural stack effect, which cause the air to rise, taking with it additional heat and 29 fostering natural ventilation . The use of a switchable device in the outer layer of a double-skin façade may yield positive effects even in this case. In winter, the device can help the natural solar heating if left in its fully-bleached position, while it can decrease the problem related to glare and contrast even without the help of additional shading devices. In summer, on the other hand, a switchable device may prevent enveloped spaces from solar overheating as above explained, and, in addition, it can also help to increase or decrease the stack effect in a solar chimney solution, since its variable colour setting can determine the level of air warming inside the cavity (3.3.8). To summarise, switchable glazing certainly has its main application in large glazed single-skin façades, but, from the thermal comfort and solar gain aspect, it still has a positive effect on double-skin solutions. The use of fully-glazed switchable façades can also contribute to augment the flexibility of office spaces, since clear openings may be set according to specific needs and variable dimensions and/or arrangements of working environments. This flexibility in the use and in the setting of the spaces, then, can further prolong the life of the building, both in environmental and social-cultural terms, with obvious economical as well as ecological benefits. On the other hand, it could even be interesting to try to couple switchable glazing with other daylighting elements, such as light-shelves, so as to implement or decrease the level of daylight penetration in the spaces, Contract ENK6-CT1999-SWIFT

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according to specific needs. For all of these reasons, it is surely clear why SWIFT systems, which can be switched back and forth between transparent and absorbing states, can be considered an ideal way to protect against sun and glare in buildings and for other solar and visual applications, while, at the same time, representing an intriguing, innovating tool, full of potential for architects and designers. If this technology does become widespread, we can expect it to change the appearance of commercial architecture in the near future. Maybe, designers seeking a uniform façade would forego the energy benefits or look for ways to mask the differences between different areas of switched modules; but, on the other hand, those who relish the idea that buildings should reflect their environments will surely find imaginative ways to employ these appealingly innovative tools.


3.3.8 Piano, Debis Tower, Berlin

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A “chameleon” skin for a sustainable architectural envelope

In order to realise Mike Davies’s idea of more than twenty years ago, the technology is now at our disposal. A “chameleon” skin able to interact dynamically with the changing weather conditions and to use natural energy sources with a minimum of technical equipment, presenting the occupants with a greater level of personal choice and interaction with the 29 environment, is then not a dream any more (3.4.1). However, despite optimism, amongst designers there are still many questions that arise about the advantages and disadvantages to these 44 systems . From the user-acceptance point of view, for example, should the switchable glazing and its control system (rather than the occupants) respond directly to varied programmatic, lighting, or thermal needs? How, why, where and when would we use devices of this type? Do users feel more comfortable or they will not accept a degree of invisible automatic control? What are the effective benefits of this type of glazing in terms of flexibility and versatility? Would we lose a degree of connection with the outside world? If the management system automatically adjusts the light transmittance of the glazing to block the sun rays from a west window on a summer afternoon, do occupants become less aware of the time of the day, the changing weather, the seasons, the movement of the Earth? Moreover, in terms of system integration: are the service systems cheap to install? Do running cost for lighting, heating and cooling effectively fall? Is the maintenance load serviceable? What happens if a pane breaks down? And, finally from the design perspective: what are the aesthetic implications of this glazing? Does using those devices can squeeze the creativity out of designers? Can they accept to live with the non-uniform 30 aesthetic of variability ?

3.4.1 The Chameleon Skin concept

The SWIFT project has actually been set up to give answer to some of those issues, clearing up many questions with regard to the opportunities and constraints of switchable glazing. However, it is important that continued research in this field will consider not only the implications of the technology in terms of energy, natural resources and visual comfort, but also its physiological and psychological impacts on human, as it has been expressed so far. In these guidelines, it has been shown how much active and dynamic systems can lead to lower energy consumption and improve the comfort level in inhabited spaces, so it is fundamental to continue support this concept, if only because it represents a need as well as a real practical possibility. 45

In fact, as market investigations showed , there is a considerable potential for the use of switchable façade technologies covering a considerable part of the shading device market, even because those technologies can be easily applied both in new constructions and in renovations, thus addressing a wide area of the building industry (3.4.2). Obviously, the specific advantages compared to traditional shading and lighting devices still have to be further investigated, in particular regarding performances assured under real application conditions, but the results obtained so far can support the idea that the use of this technology may provide, in an eco-efficient way, a reliable and “clean” building cladding, able to incorporate simultaneously the functions of high-performance windows, efficient solar shading and daylight provision, contributing very much to the aim of improving the quality of life, health and employment 46 through a better comfort in working and living spaces . In fact, if we consider that most buildings in Europe still employ single and double glazing with uncoated glass, and essentially rely on the use of air conditioning to guarantee comfortable conditions in inhabited space, it is easy to understand how, theoretically only by replacing those windows, a huge technical potential in terms of primary energy savings could be Contract ENK6-CT1999-SWIFT

3.4.2 Market Potentials

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inferred, that will correspond to a significant reduction of CO2-emissions. And if the ”developed” world is to meet the emission reduction targets outlined in Kyoto, energy savings from advanced technologies can surely play an important supporting role (3.4.3). However, in order to reach those energy savings, economical considerations, as cost-benefits and renovation cycles, have to be taken 41 into account. It has been estimated that, without being specific to future costs of installed SWIFT façades, either in the form of cladding walls or window technology, a utilisation of only 5-10% of the technical potential as economical market will probably result in 20-30 billion Euro market over a period of about 20 years (i.e. roughly 1-2 billion Euro per year) only in the renovation of existing buildings. In addition, with the starting up of the market and the consequent probable fall in the primary costs of this technology, the installations in new buildings may add to this figure, while the opening of other markets, as for example United States or south-east Asia, which are believed to be climatically favourable for the application of switchable façade technologies, could further increase their economic importance. On the other hand, if we consider that the lifetime and reliability of those devices is believed to be very high, compared to traditional products, it is easily understandable the reason why switchable façades are seen to represent a big step towards a more “sustainable” building envelope. Moreover, if governments are serious about industry development and a more energy efficient economy with low environmental impacts, it is also foreseeable the setting up of specific policies and market interventions that can create investments in the removal of barriers for the spreading of these innovating devices, while the design community can help to educate themselves, their colleagues, and their clients to create a market pull for 47 the technology .

3.4.3 Effects of global warming

As a matter of fact, if we make a comparison to some recent advances in glazing technology, as for example the application of high efficient lowEmissivity coatings, we may see that it took about 15 years to them to get to the 35% market penetration level, with a reduction in cost from about 43 500 to 5 €/m2 . Nevertheless, even if the market penetration of switchable glazing could be thought as being slower, since low-E is a much simpler technology that does not require all the integration into the building's electrical and management systems, it must be considered also that lowE's slower-than-expected market penetration was also a result of the fact that consumers could not "see" their benefits (3.4.4). On the other hand, the fact that the SWIFT windows can actually be “seen” switching could surely help people to understand the advantages they 42 deliver and maybe it will speed their availability and market penetration . In any case, a real new challenge is emerging to architects and designers that will have to give shape to those ambitions, so it is of fundamental importance that the improvements in the glazing industry for a high-quality building skin go together with the setting up of advanced energy and management concepts, so as to guarantee the interaction of the façade with the whole building and its components. Therefore, basing on the strict connection between technical and scientific information, innovating capacity and practical applications, a detailed and specific knowledge of the “new technologies”, in the field of innovating materials and control systems, will be inevitably required even to the designer, in the hypothesis of a technology transfer into sustainable architecture. The carrying out of this concept will surely pass through the assumption of a new design attitude, which has, nevertheless, to be accounted in a more Contract ENK6-CT1999-SWIFT

3.4.4 An EC (left) and a low-E Glazing

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“holistic” approach. Indeed, as explained above, the application of dynamic and interactive glazing systems is a projectual theme of huge interest, and thus it can not be relegated to the area of a formalistic experimentation or in the a-critical consideration of a fashion phenomenon. It follows that the designer has to assume a sort of “transversal” knowledge, organising it not specifically on detailed physical and material aspects, but rather on the possible functions, options and further chances they can assure. The role of the designer has to be enriched with new competence, new technical instruments that can reorient and reorganise the project; actually, it could be considered as a sort of “bridge” between different cultural and scientific contexts, trying to overtake their dialogue difficulties, towards the exploitation of the new technological potentialities and innovating solutions.

3.4.5 A new horizon is looming!

In any case, a new horizon is looming, and the principles discussed so far are probably only a beginning (3.4.5). Nevertheless, the prophetical words of Mike Davies suggest that there may be no better place to be: “A clear future for advanced high performance glass-based products exists; it is essential that multidisciplinary groups are brought together to combine diverse skills. Much knowledge exists; it is really a question of the intelligent and creative combination of science and industry. Over and above the clear technological potentials of glass, architects have not in the least lost sight of its potential beauty and visual performance. The polyvalent wall, a dynamic processor should not only be the logical response to a dynamic environment at a technical performance level but also fulfil the role of magician in its visual potential and virtuosity. Look-up at a spectrumwashed envelope whose surface is a map of its instantaneous performance, stealing energy from the air with an iridescent shrug, its photogrids as a cloud runs across the sun; a wall which as the night chill falls, fluffs up its feathers and turning white on its north face and blue on the south, closes its eyes but not without remembering to pump a little glow down to the night porter, clear a view-patch for the lovers on the 29 south side of level 22 and to turn 12 per cent silver just after dawn” .

3.5

References

27. Wigginton M., Glass in Architecture, Phaidon Press, London, 1996. 28. Davies M., “A wall for all seasons”, in RIBA Journal, vol. 88, n. 2, February 1981. 29. Compagno A., Intelligent Glass Façade – Material, Practice, Design, Birkhauser, Basel, 1995, rev. ed. 2002. 30. Wigginton M., Harris J., Intelligent Skins, Architectural Press, Oxford, 2002. 31. Lee E.S., et al., “Active Load Management with Advanced Window Wall Systems: Research and Industry Perspectives”, in Proceedings from the ACEEE 2002 Summer Study on Energy Efficiency in Buildings, Asilomar, August 2002. 32. Lee E.S., Di Bartolomeo D.L., Selkowitz S.E., “Electrochromic Windows for Commercial Buildings: Monitored Results from a Full-Scale Testbed”, in Proceedings of the ACEEE 2000 Summer Study on Energy Efficiency in Buildings, Asilomar, August 2000. 33. Selkowitz S.E., Lee E.S., “Advanced Fenestration Systems for Improved Daylight Performance”, in Daylight ’98 Conference Proceedings, Ottawa, May 1998. 34. Selkowitz S.E., “Integrating Advanced Façades into High Performance Buildings”, in Proceedings of the 7th International Glass Processing Days, Tampere, Finland, June 2001. 35. Flabeg Pilkington, EControl®- The thermal multitalent, Architectural Products, 2001. 36. Zinzi M., “User response in an occupied office room equipped with manually switched electrochromic devices”, in WP3 - SWIFT Project, 2003.


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37. Tenner A.D., “Switchable Facades and Visual Comfort; results of first user assessments”, in WP3 - SWIFT Project, December 2002 38. Lee E.S., Di Bartolomeo D.L., “Application issues for large-area electrochromic windows in commercial buildings”, in Solar Energy Materials and Solar Cells, May 2000. 39. De Herde A., Reiter S., L’Eclairage naturel des batiments, Architecture et Climat – UCL, Ministère de la Région Wallonne, 2001. 40. Lee E.S., Selkowitz S.E, “Integrated Envelope and Lighting Systems for Commercial Buildings: a Retrospective”, in Proceedings of the ACEEE 1998 Summer Study on Energy Efficiency in Buildings, Asilomar, June 1998. 41. Commission for the European Communities, Switchable Façade Technology - SWIFT Project, Progress Period 4 (24th Month), June 2002. 42. Adereck K.J., “Transforming Exterior Walls with Electrochromic Windows”, in Environmental Design+Construction, 25 November 2001. 43. Selkowitz S.E., “High Performance Glazing Systems: Architectural Opportunities for the 21st Century”, in Proceedings of the 7th International Glass Processing Days, Tampere, Finland, June 1999. 44. Guzowski M., Daylighting for sustainable design, Mc Graw-Hill, 2000. 45. Commission for the European Communities, Switchable Façade Technology - SWIFT Project, Midterm Assessment Report, October 2001. 46. Travi V., Advanced Technologies, Birkhauser, Basel, 2001. 47. Prasad D.K., Snow M., “The Role of Emerging Technologies and Tools in ‘Green’ Buildings”, in Proceedings of the PLEA 2002 Conference, Toulouse, July 2002.

3.6

Iconography


- Images n° 3.1.5, 3.4.2 are courtesy of José Flémal (UCL). - Image n° 3.1.7 is taken from the Gimp-Savvy Copyright-Free Web Site: http://www.gimp-savvy.com/PHOTOARCHIVE/. - Images n° 3.1.8a, 3.1.8b, 3.2.5, 3.2.22 are taken from Flabeg E-Control® Brochure: Flabeg Pilkington, EControl®- The thermal multitalent, Architectural Products, 2001. - Images n° 3.2.9a, 3.2.9b, 3.2.13 are taken from the Project SWIFT Documentation Report: Commission for the European Communities, Switchable Façade Technology - SWIFT Project, Midterm Assessment Report, October 2001, swift-coord-mtr-011031-midterm report.pdf. - Images n° 3.2.10a, 3.2.10b, 3.2.14 are courtesy of Helen Rose Wilson (Fraunhofer-ISE, Interpane). - Image n° 3.2.12 is taken from the Project SWIFT Documentation Report: Wilson H.R., Heck M., “Results of Visual Inspection”, in WP2- SWIFT Project, 2002, swift-wp2-ip-020626-visual_inspection_results_v3.pdf. - Image n° 3.2.24 is courtesy of Markus Heck (Fraunhofer-ISE). - Images n° 3.3.1, 3.3.2a, 3.3.2b, 3.3.2c are courtesy of Jan Wienold (Fraunhofer-ISE).


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4 Description of the case studies 4.1

Practical integration of an Electrochromic façade at TU Eindhoven

In the context of Building Integration, a full-size test Electrochromic (EC) façade has been designed, built and installed in an office building of the TU/e, the Technical University of Eindhoven (NL). On the basis of architectural considerations, the owner of the site imposed some restrictions on the installation of the glazing, determining intensive planning; those challenges could be met having University of Louvain as architectural guidance. The available chosen room is 3.6 m wide, 6.2 m deep and 2.6 m high; the windows, facing East, reach from 0.88 m above the floor to the ceiling and are divided vertically in 3 parts; walls and ceiling are white and there is a 48 blue-grey carpet on the floor (4.1.1). The planning and design of the façade involved a methodology that took account of the orientation, the sun elevation, the EC properties, building and window functions, the benefits of the environment, but also the 49 protection of building and its users from external and internal nuisances .

4.1.1 SWIFT test room, Plan view

At the design stage, three fundamental issues have been considered. The first one was to demonstrate the importance of designing the electrochromic façade considering the specific goals related to each window functions. The second issue was to show the importance of integrating these devices into architecture; it is, in fact, always fundamental to pay attention to context integration, space functions, organisation and orientation. For new constructions, the choice of EC glazing has to be taken in account at the early beginning of the project; for renovations, on the other hand, it is important to understand how this new technology can be involved in the existing context, which are its nuisances and its positive contributions. The third one was to demonstrate that often switchable glazing is not the unique solution; it can not be applied everywhere and is not an answer to every problem, while some goals can be reached by other means (normal or low-E glazing), thus showing that simple solution can sometimes answer much better to defined aims of the project, on a technical, economical or human level. The design of the façade considered the variation of the sun position in the sun-path, the different functions of the windows, the zoning of the office test-room for daylight, glare problems, and overheating protection. Course of the sun and façade orientation Four different zones have been defined considering the usual working hours and the east-orientated façade, the sun evolution between 7 and 12 am (in universal hour) and its azimuth (-90° to 0°) (4.1.2): §

In Zone 1, the height of the sun is lower than 20° and the azimuth varies from -80° to 0° (7 to 12 am); in this position the sun can be a source of direct glare when the sky is clear.

§

In Zone 2, the sun rises rapidly (from 20° to 48°), in a short time (7 to 8.30 am) and with a limited azimuth angle (between -90° and -65°), corresponding to a vertical path on the graph. Considering the rapid sun evolution in this zone, the window should be divided up horizontally in many independent frames.

§

In Zone 3, the sun does not rise as rapidly (7.30 to 11 am) as in zone 2; the graph begins to tend towards the horizontal. The height is comprised between 20° and 60°, while the azimuth varies from -65° to 20°. The window does not have to change its properties so rapidly and could be less divided up.


4.1.2 Solar Graph

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In Zone 4, the graph tends to be horizontal (10 to 12 am). The path of the sun does not rise anymore, with a height comprised between 20° and 62°, and an azimuth angle comprised between -20° and 0°.

Definition of different zones inside the office Considering the façade orientation and the structural aspect of the window, three different zones have been defined inside the office space, corresponding to a visitor zone, a user zone, and a desk zone; obviously, the functions could move inside each zone (4.1.3). To protect the user from glare caused by indirect reflections, the computer screen should be placed in a position perpendicular to the façade, and at a certain distance from it, but always keeping a circulation area around the desk and enough space for door opening. The desk zone would thus preferably be placed in zone A.

4.1.3 Zones definition

As above described, the sun responsible for direct glare in the office has an azimuth angle contained between -80° and 0°; considering that this effect can not be completely avoided by an EC glazing in its fully-coloured state, the user should preferably turn his back to this sun azimuth and therefore face the northern wall. The user should be placed everywhere along the southern part of the desk, corresponding to zone B. The visitor obviously will use the office less often, so his protection against direct glare effects is less important. It can be considered that the visitor faces the user area, being collocated in zone C. Anyway, in the general planning of the office room, it has been considered that some people could prefer to use the zone C. Hence, they could avoid indirect glare due to screen reflection or north wall reflection, but, as they face the sun coming from south-east, they could be bothered by direct glare. In this case, the window surface to be switched could be bigger, especially if the surface desk has to be protected from solar radiation too. Glare According to the visual angle of the glare source, the user could feel a more or less important discomfort; we can distinguish a glare zone (0°-5°), a tiredness zone (5°-10°), a trouble zone (10°-20°) and a discomfort zone (20°-40°) (4.1.4). However, the glare notion depends also on the human sensitivity, cause when exposed to a light source, each person will not have the same visual feeling. If the user is placed in zone B, he is naturally partially protected from direct sun; obviously, this is not the case if he is placed in zone C, cause he faces south-east. The EC minimum visible transmittance is too high to protect users from direct glare in clear sky conditions; consequently, the low sun, with an height comprised between 0° and 10°, could be uncomfortable for everyone and thus shading devices have to be purposely designed, as, for example, an internal blind system to be rolled down between 1.2 and 1.7 m. Anyway, since in this case the azimuth angle varies between -50° and 0°, the area of the window to be shaded only corresponds to the frames placed on the right. A shading device could also be placed in the central area of the window to protect the visitor, but should not have to be rolled down at any time. When the sun elevation is contained between 10° and 20° - thus corresponding to a trouble zone on the glare graph - the EC can assure a visible transmittance low enough for some users but not for others; so, even in this case, it would be better to ensure the user with an additional shading device, possibly independent from the previous one, and that could cover the height comprised between 1.7 and 2.3 m. For a sun elevation in the range between 20° and 40°, the switchable gl zing c n prevent gl re in cle r sky conditions while when the sun is Contract ENK6-CT1999-SWIFT

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glazing can prevent glare in clear sky conditions, while when the sun is higher than 40° on the horizon, the user is naturally protected by the shade provided by the ceiling. Indirect glare As indirect glare always results from reflected light, the visible transmittance modification of switchable windows can prevent this effect. The part of the window to be switched to the fully-coloured state is anyway the same that protects the user from direct reflection, while, if the user is very sensitive and would not feel the EC minimum transmittance is low enough, the blind designed to protect users from direct glare can also contribute to avoid indirect effects. Regarding glare on a VDT, it must be considered that a computer screen is a specular surface, so the user can be bothered by intensive light coming from its back. However, if the user takes place in zone C, the screen turns its back to the sun and there is no more danger of indirect reflections; the same could apply for northern wall reflections. If the occupant takes place in zone B, he could be rather disturbed by the white colour and by light reflections on the wall. A first solution could have been to paint this wall in a mat colour, a little bit darker, but this would have reduced the general light level and also increased the contrast between the window and the back part of the office. An alternative solution would have been to place an electrochromic glazing even on the left part of the window so as to protect this wall, but this would have represented a large financial outlay for something that could be resolved in another way. On the other hand, it is has been considered also the interest of equipping at least the left part of the window with a low-E glazing, provided that a blind system avoid indirect reflections, so as to show that switchable glazing and its complexity have to be designed considering a whole of parameters that include, of course, also economic means. Concerning desk surface reflections, one can determine which glazing area has to be switched in order to shadow the desk at any time, according to the different zones of the sun elevation above defined (4.1.5). If the sun is situated in zone 1 and the desk surface is diffusing, there will be probably a glare risk; for sensitive users, the right and central parts of the window comprised between 0.8 and 2.2 m should be switched in their coloured position so as to shadow the desk. In this zone, the sun height can change slowly, so the frame should be very divided up horizontally, in order to optimise the switched glazing area; this division could also permit a reduction of the switching time. With the sun in zone 2, the EC window should be switched between 0.8 and 2.8 m, so as to protect the desk surface from direct sun. On the other hand, the switching of the panes comprised between 2.2 and 0.8 m could protect the occupant from sun positions higher than 26°. However, it must be considered that in this zone the sun takes only a few minutes to rise from 20° to 26°, so it would make no sense to further complicate the frame design in order to take care of an early short period of summer sun, both for functional and aesthetic concerns.

4.1.5 Direct and indirect glare

If the sun is situated in zone 3, the EC window should be switched between 0.8 and 2.8 m, so as to shadow the desk, while, as in zone 2, the upper-switched window would not be necessary for a sun height between 20° and 26°. However, since in this case, the sun rises less rapidly, it could be interesting to take care of this low sun and to increase the horizontal frame di i i i th t I l i th f di i i b t 08 Contract ENK6-CT1999-SWIFT

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division in the upper part. In conclusion, the frame division between 0.8 and 2.2 m should be minimal, while for the window part higher than 2.2 m, the division could be greater. With a sun height corresponding to zone 4, if sensitive users put their desk close to the façade, the right-switched window could protect them from indirect reflection. Actually, as already mentioned, in this part of the graph the sun rises very slowly and the curve is very horizontal. The central part of the frame should then always be switched, while the upper frame division should be bigger to take advantage of each evolution of the sun. As a conclusion, this analysis has highlighted the need, for the right part of the window, of a lot of horizontal divisions between 0.8 and 2.8 m (zone 1); a few horizontal divisions between 0.8 and 2.8 m (zone 2); a few horizontal divisions between 0.8 and 2.2 m and a lot of horizontal divisions between 2.2 and 2.8 m (zone 3); a few horizontal divisions between 1.7 and 2.2 m and lot of horizontal divisions between 0.8 and 1.7 m and between 2.2 and 2.8 m (zone 4). For the central part, on the other hand, it would be advisable to have a lot of horizontal divisions between 0.8 and 2.2 m (zone 1); a few horizontal divisions between 0.8 and 2.8 m (zone 2); a few horizontal divisions between 1.7 and 2.2 m and lot of horizontal divisions between 0.8 and 1.7 m and between 2.2 and 2.8 m (zone 3). As a consequence, a lot of horizontal divisions would be necessary on the right and central frames of the window, while no particular horizontal divisions are needed on the left part of the façade. Consideration should be given to the visually disturbing effect of many divisions. Overheating protection Since the façade is oriented towards East, horizontal shading devices or overhangs would be ineffective to protect the window from direct sunrays. Vertical shading devices could be suited to the case, but they would reduce the daylight level at every moment, even when not necessary; moreover, if they were seasonal, they could also be expensive. The use of an electrochromic device thus seems to be a good solution in this case, because of its possibility to reduce the solar heat gain coefficient; switching to a dark state the two thirds of the entire window surface can considerably reduce overheating, while the third left can continuously provide daylight supply. Nevertheless, switching the bigger part of the window would also considerably reduce the average daylight level, so it must be considered the alternative solution of shadowing the user, so as to reduce the portion of the window to be left in a fully-coloured state and to improve the daylighting, while always reducing solar gains. A shadow on the occasional visitor could be less accurately designed. For a sun height between 0° and 20°, blinds can shadow the user zone, so switched window has only to be designed for a sun elevation comprised in the 20°-60° range. If the user takes place at 1-3 m from the façade, the part of the window to be switched should correspond to a height comprised between 1.1 and 2.8 m. On the contrary, if the user is placed at more than 3 m and the sun is high on the horizon, the lower part of the window could be bleached; when he is at less than 1 m from the façade, and the sun is low, the upper part can be bleached (4.1.6). As a consequence, the window should be divided up horizontally in several parts, so as to take into account each sun elevation and weather modification that can be important in this geographic situation.


4.1.6 Overheating protection

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If the user takes place in zone C, the area of the window to be switched could be even more important, especially if the desk has to be protected too. Consequently, the office shadow area could be bigger, thus reducing daylight supplies, and, for this reason, the central and the right part of the window would need a lot of horizontal divisions. The user is protected from direct sun radiation by the central or the right part of the switched glazing for an azimuth between -70° and 0°. When the sun azimuth is between -80 and 0°, the occupant is protected if he is placed at a distance of at least 2 m from the façade. When the sun reaches the -70° azimuth, this minimum distance falls down to 1 m. Anyway, as we can see in the sun path diagram, when the sun azimuth is between -90° to -70°, it is early morning, and at this moment, the sun takes only little time to pass over the -70° azimuth, all the more reason why there is no strict need to have an electrochromic glazing in the left part of the window.

4.1.7 Design solution 1

On the contrary, this part could be equipped with a standard low-E glazing, in order to provide continuously a colourless view and also to foster natural ventilation, if fitted into an openable frame. Light supplies The visual depth of the office could be reduced by working on colours or on the false ceiling design, linking it to the façade so as to improve daylight penetration inside the office. Ventilation, external views and physical contact with the external world The upper parts of the window should be openable so as to ensure natural air circulation, thus helping maintain a good level of air quality and evacuate the overheating during summer. The left part of the window could assure a continuous unobstructed view to the outside, since it does not need particular horizontal divisions nor shading systems, as from the analysis carried above.

4.1.8 Design solution 2

Moreover, opening this window frame it would be possible to enhance natural ventilation and to keep visual contact with the outside. Conclusions This analysis process has brought to a first design of the electrochromic façade providing the right and central part of the frame divided up horizontally in four parts to take into account the rapid sun evolution and its influence inside the office. By doing that, it becomes possible to switch to a coloured state just the part of the window responsible for glare or overheating. A non-electrochromic sun-protective low-E glazing has been placed on the left and upper parts of the window, and fitted into openable frames so as to assure a natural view and ventilation, thus providing a good air quality level and the overheating evacuation. Two blinds have been designed at 1.7 m from the floor; the first should be rolled down to 1.2 m and the second should be rolled up to 2.3 m (4.1.7). This architectural solution for the pilot façade, has been subsequently further developed, according to the available size of electrochromic frames and to contextual situations. A new scheme has been proposed and realised based on the same principles, but with an horizontal division of the frames providing two upper and lower low-E smaller openable frames (from 0.8 to 1.2 m and from 2.4 to 2.8 m), and just two EC panes (instead of 4) - with black frames on the outside and white on the inside - in the right and central part of the Contract ENK6-CT1999-SWIFT

4.1.9 The final EC Façade

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window, covering a height from 1.2 to 2.4 m (4.1.8). The left part of the window has initially been equipped with a lowEmissivity glazing to ensure visual contact with the outside, but it has later been changed into an electrochromic too. This was due to the occurrence of major contrast problems caused by big luminance differences between the left “transparent” panes and the central and right EC frames, especially when they were switched to their fully-coloured state. So, at the end, the electrochromic glazing has been installed in six 48 individual panels, in two rows of three panels above each other (4.1.9). The room has been furnished in a “standard” way, as a single cell office with an L-shaped desk, a conference table, dark blue chairs and a cupboard with yellow sliding doors (4.1.10). The user has been placed in zone C - compared to the previously explained zone definition - so as to experience the worst-case condition of the test room. The electrochromic façade has been equipped with a separate controller to modulate independently the state of each glazing, and an adapted modern lighting systems has been installed by Philips.


During the tests, people have been asked to work for several hours in the test room and have then been questioned about their preferred lighting conditions and well-being.

4.2

Practical integration of an Electrochromic façade at office room in Rome

One of the aspects of Building Integration is the evaluation of the users response and acceptance of the switching glazing technology. To obtain data and information about this issue and experiment of an occupied office room equipped with electrochromic windows was carried out at the experimental building “Casa Intelligente”, built in the research centre ENEA CR Casaccia, located in the northern outskirts of Rome. The experiment aimed at verifying if and how the smart glazings can improve the indoor environment (especially the luminous one), integrated with other shading devices and with the artificial lighting system. The experiment was carried out giving the users the possibility of setting the different light sources of the room according to their requirements. The lighting dynamics were, hence, manually run, without any planned remote control. (4.2.1) 4.2.1 Test room in Casa Intelligente

Test room The room is a 3.13x4.2 meters, it has two windows one facing west and one facing north. The window size is 1.2x1.6 and the total glazed surface is 1.2 square metres. During the experiment one subject was in the room, and he was allowed to modify the status of the west windows only, the other window always remained in the clear status. The north window remained in the clear status to check if the windows in different coloration status may affect or disturb the luminous environment for occupants. The working desk with a personal computer was located as in figure 4.2.2. An additional and movable semitransparent blind (luminous transmittance 50%) was mounted behind the window, to be used by the occupants if more shading was required during the test. The EC controller was placed on the working desk, in order to facilitate the user operations.

4.2.2 Test room plan

The artificial lighting system consisted of four luminaries, each of them using 4 lamps of 18 Watts. The lighting system is of a dimmable type, it can be remotely automated and controlled, or manually switched by the user. At maximum power an illuminance of 1000 lux is measured on the Contract ENK6-CT1999-SWIFT

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working plane.

Occupants The experiment was carried on between the beginning of August 2001 and the beginning of October 2001. The text was carried on 30 users, half men and half women, the age was comprised between 23 and 63 years with an average of about 40 years. During the test all of them should sit and do usual office work including reading, writing and working at the computer station. The users had different educational background.

Experiment The main idea of the experiment was to give to the occupants the chance to choose the most comfortable visual environment, by regulating the dynamic glazing system and the dimmable artificial lighting. The initial conditions of the room were the same for all the participants at beginning of the experiment, excluding, of course, the climatic conditions. Then they were free to operate the facilities of the room according to their needs and requirements. The starting time of the test was fixed in the afternoon, when usually the lumiance of the sky for the west facing window was quite high, and darkening of the room seemed necessary. When the conditions are not satisfactory, the occupant starts changing the lighting systems, both natural and artificial, trying to achieve the maximum comfort. This include darkening the glazings, pulling on and off the blind, switching on and off, and dimming the artificial lighting. Illuminance levels on the working

At the end of the afternoon, a questionnaire had to be filled in, with questions related to the luminous environment, but also to the operation of the various facilities and the general feeling of the users with respect to the the dynamic glazing systems.

Averaged values between 15.05 and 30.0

6.7

6.7

Monitoring results The monitoring of data acquired during each single test, together with the visual inspection and the notes taken during the experiment, gave the possibility of collecting information on illuminance levels for different sky conditions in the room. During the 30 days of test, 3 main sky conditions were identified, which were categorised as follows:

20.0

EE>300 500>E>400 600>E>500 800>E>600 1000>E>800 E>1000

6.7

6.7

23.3

4.2.3. Percentage of the illuminance level on the working plane

1. Clear sky

Daylighting levels on the working plane Averaged values between 15.05 and 16.05

2. Sky partly cloudy with a direct solar radiation component

13.3

3. Overcast sky 46.7

The averaged preferred illuminance for using artificial lighting was 580 Lux. It can be seen that the 93% of the users chose a luminous environment with giving more than 300 lux on the working plane, and in the 57% of the cases the required level was higher than 500 lux (4.2.3). Using daylight, also in this case the 93% of the users chose a luminous environment with giving more than 300 lux on the working plane, but the number of users requiring more than 500 lux decreased to 33%. Concerning the detailed results, it can be seen that 2 users wanted less than 300 lux of daylighting, around 20% between 300 and 400 and the 4.2.4. Percentage of daylighting level on the working plane majority (54%) between 400 and 500 lux.(4.2.4) 6.7

13.3

EE>300 500>E>400 600>E>500 800>E>600

20.0

For clear sky the majority of users used the full colouring potential of the electrochromic windows (70% used full colouring equivalent to setting 5, see 4.2.5). The use of an additional roller blind with 50% visual transmittance was favoured by remarkable 50% of the test persons – they Contract ENK6-CT1999-SWIFT

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wanted to decrease glare even further although no direct sunlight was on the working plane and the window was already fully coloured. The lighting level in general seemed very often high enough just with daylight, as more than 56% of the users never used artificial lighting in that period, and all others dimmed that light according to their needs (4.2.6). So a qualitiative result is certainly that switchable glazings can reduce glare without necessarily increasing the need for artificial lighting. The results indicate that users tried to tune very accurately the various systems for the personal demand of light, starting with the colouring of the glazing.

EC-glazing status Prevalent position between 15.05 and 16.05 6.7 10.0

6.7

6.7

1 2 3 4 5

70.0

Questionnaire results A qualitative analysis of the visual comfort in the full scale test rooms was adopted by means of interviews and questionnaires. The answers ranged from 1 to 5 according to the complete agreement to the complete disagreement with the question.

4.2.5. Percentage distribution of electrochromic colouring set point (clear sky)

The questions to be answered by the users were divided in three different phases of the experiment, the first one after the subject got familiar with the test room, the second after he changed the luminous environment of the room according to his/her preferences, and the third at the end of the test, with question related also to the general feeling of the person versus this new technology.

EC-glazing status Prevalent position between 15.05 and 16.05 6.7 10.0

6.7

6.7

When the persons came into the room with uncoloured glazings, more than 70% were quite comfortably with the luminous environment, with a tendency that the situation was a bit too bright, and that external sources would cause glare.

1 2 3 4 5

When people changed their visual environment according to their feelings, about half of the group felt that they would prefer a quicker switching time. The possibility of adapting the window colour, however, resulted in a much 4.2.6. Percentage distribution of electrochromic colouring set point (clear sky) better evaluation of the glare situation. The number of person dissatisfied with the luminous environment decreased very much down to 17% (for external glare) resp. 13% for glare from internal objects. The benefits of the electrochromic windows were clearly apreciated. (4.2.7). 70.0

Question 5 & 11: presence of glare from outside with the glazing bleached and coloured

50

It is interesting to note that after colouring only a small number of users even notice a change of perception of the inner environment, whereas most of the users (60%) notice the change of the outdoor view. Accordingly less than 7% of the test persons bothered about a change of perception due to the colouring of the windows. With respect to operation most persons liked the manual operation although a smaller group also would prefer automated controls. This is different for the operation of the roller blind where many persons were discontent with the manual operation.

40 Window Bleached Window coloured

30

20

10

0 1

2

3

4

5

na

In total the test persons were very positive about the new technology. 84% said that the system was helpful to improve their visual comfort, and less than 10% thought it not very useful.

Summary •

Switching glazings are very useful to improve the illumiannce level on the working plane, the glare control and the visual comfort. In case of direct sun and high luminance of the sky, the actual luminous performance of the systems make necessary the presence of further shading devices. The reduction of amount of light inside the room can be adequately and rationally compensated by the installation of a dimmable lighting system.


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•

The switching time is an important issue to be analysed. These systems reuire some minutes for changing their status, hence they cannot switch according to the quick variations of the sky. Even in more stable conditions, the colouring of the glazing inputted by the user might come to the end when the visual discomfort has already occurred, especially when the deeper colouration of the window is chosen.

•

The alteration of the outdoor environment due to the colouration process is often perceived and generally well accepted. Not many changes are found in the internal environment. More over the presence of glazings with different colouration depth seems not to significantly bother the majority of the users. The situation might heavily change in case of large glazed facades instead of the hole in a wall windows of the ENEA experimental building.

•

The mix of natural and artificial light can bother several users, this is an interesting issue but more investigation are needed in this fields. The limit of the present experiment included the limited number of subject that used the artificial light and the use of only one lamp and luminaries type. Interesting results may arise by the analysis on the use of different artificial light sources mixed with bluish coloured light transmitted by the electrochromic devices.

•

The wide majority of the users are not bothered by manually operating the glazing, blind and artificial lighting systems. On the other side, this percentage is quite reduced when asking if an automated control might be appreciated. This is a debating argument, but the findings of the questionnaire stress that the possibility of manually setting the various lighting sources of the room, is the preferred choice of the majority of the users.

4.3

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Practical integration of switchable glazing in offices in Freiburg

Facade integration During the SWIFT project, a switchable facade for two office rooms is integrated into the building of Fraunhofer Insitute for Solar Energy Systems (ISE). These offices are typical offices with a depth of 5 m and a width of 3.75 m. Looking from the inside, the facade has two transparent parts: An upper one, which should guide the light into the room depth and a lower one for the view. In each of the rooms a different switchable facade systems (GC and EC) have been installed in autumn 2002. Both systems have been installed in such a way, that the overall impression of the facade has not changed, besides the colour of the glazing and the non-use of the blinds in those offices. The rooms are located in the basement floor (position see picture). All offices are ventilated by an exhaust ventilation system in combination with manual opened windows. There is no active cooling installed.

EC

GC 4.3.1. Outside view of the building, with the GC and EC integration

The main purpose of this installation is to demonstrate, that the switchable façade technology is not so far from the market and building integration is already possible. A second aim of this installation is to gain experience in the daily use and control of the systems, even if the installation is in only two rooms and real representative user assessments are not possible.

Monitoring design For the SWIFT project, these office rooms have been monitored to have Contract ENK6-CT1999-SWIFT

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the possibility to evaluate performance indicators of the façade. But the main purpose is to gain experience of the façade system in a real used office and to see how the temperatures in the rooms develop in comparison with a conventional system (outside mounted venetian blinds). The measurement of the two rooms is embedded in the measurement of 16 rooms of the same part of the building. Following measurands are monitored: •

Room air temperature

•

Room perception temperature (Globe temperature)

•

Illuminance on workplace

•

Presence of occupant

4.3.3. Inside view of the GC installation

Results The measurement period was in the first hot weeks of the late spring of 2003.

Room temperatures The building integration of switchable facades in a used office building is difficult to evaluate, since the use (which means the internal loads and times of opening the windows and doors) of the rooms vary and consequently the rooms behave differently. Therefore it was decided to evaluate the temperatures on a Sunday, where in all offices is no occupation and the weather situation was stable sunny the days before.

4.3.4. Inside view of the EC installation

In the following two graphs, the general situation is shown. After a long hot period, the building has a high average temperature (about 27°). All rooms in the ground floor are in the same temperature range. The ambient temperature drops down during the night to 18 °C and has maximum values up to 30°C. The evaluated day was a sunny day with only few clouds only in the afternoon (see irradiation graph). The detailed evaluation of the temperature curves show, that the GC equipped room has quite the same temperatures than the reference room. This is a very important result, since the venetian blinds of this reference room is completely closed, also the day before. The EC equipped room lies 0.5 °C higher in average than the GC equipped or the reference room. The difference is very small, but can be explained: The g-value is somewhat higher

•

The constant internal loads are higher (146W for EC-office vs. 82W for GC-office

In the case, when the sun hits the facades and the ambient temperatures rise, the gradient of the rise for all three offices is the same, which means, that the influence of g-value difference is small in comparison with the rise of the outside temperature.

Temperature [°C]

•

4.3.6. Occupancy sensor 30 29 28 27 26 25 24 23 22 1:RT_C105 21 2:RT_C107 20 3:RT_C109 (Reference) 19 4:RT_C111 18 5:RT_C113 (EC) 17 6:RT_C115 (GC) 16 Ambient Temperature 15 0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00 local time

4.3.8. Temperature behaviour of switchable façades offices in comparison with similar rooms of the same floor level

Desk illuminances during use of the room One of the main advantages of the switchable systems can be demonstrated with the illuminance evaluation. Having the full sun protection activated (the system are switched to the darkest mode), the Contract ENK6-CT1999-SWIFT

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system still offer view to the outside and provide the room with plenty of daylight. This can be seen in the following graphical evaluation. During real occupation (shown are only values, when in all offices are at least 1 person), the illuminance values are 3-5 times higher than in the reference room(s). Due to the higher visible transmittance, the average illuminance levels for the EC equipped are in average higher than for the GC room.

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Radiation on vertical south facade [W/m²]


1000 900 800 700 600 500 400 300 200 100 0 0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00 local time

4.3.9. Global irradiation on the vertical south façade (=room orientation)

But it must be mentioned here, that no additional glare protection has been installed yet, which will lower the illuminance level.

28.2

3:RT_C109 (Reference) 5:RT_C113 (EC) 6:RT_C115 (GC)

28.1 28

Conclusions of the office measurements •

•

Compared to a very effective conventional system (outside mounted venetian blinds), the switchable glazing rooms tend to be in the same temperature range.

Temperature [°C]

27.9 27.8 27.7 27.6 27.5 27.4 27.3

Shading from other building

27.2 27.1 27

26.9 00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 00:00 local time

At hours, when the systems are in sun protection mode, the switchable Detailed temperature behaviour façade rooms equipped have 3-5 times higher illuminance levels than 4.3.10 of the switchable façade offices in the rooms with the venetian blinds. This illuminance level will be comparison with one reference room on the same floor level. During solar reduced, when an additional glare protection system will be installed. penetration, the gradient of temperature rising in all rooms is the same

4.3.1.1 Evaluation of user comfort and acceptance in test rooms

2500 C105 (2nd reference) C109 (Reference)

The main goals of the user assessments in test rooms are:

Desk illuminance [lux]

2000

C113 (EC, colored state 5) C115 (GC, colored)

1500

1000

•

To find out the general acceptance of the system

•

Is an additional glare protection necessary, when sun doesn’t hit the eye of the user?

•

Colour temperature: Is there any unpleasant colour shift noticed by the 4.3.11 Average luminance levels on the workplaces in the evaluated rooms .The users? illuminance levels for the switchable

Methodology

500

0 0

10

20

30 40 50 hours of identical presence

60

70

80

facade rooms are remarkably higher (35 times) than those on the reference rooms. Shown are only those hours, when all evaluated offices are occupied.

To find answers to above questions, user assessments in office like test rooms has been performed. The test rooms at Fraunhofer ISE in Freiburg, Germany are fully rotatable and consist of two identical rooms. One of the rooms has been used for the user assessments (called “test room”) and the other for the measurements (“reference room”). The reference room is needed to assure, that the conditions during the tests are quite constant and also not to different between the subjects. A gas-chromic system has been installed in both rooms. The switching takes place parallel, so that the switching state is similar in both rooms. The switching is done by a switch on the table, the subjects have access to it. The design of the tests strongly depend on the goals of this task. To find the general acceptance, it is necessary to operate the system in both states. To find answers to the glare issue, it is necessary to run a test with an additional glare protections system (white venetian blinds).

4.4.1 Outside view of the rotatable test rooms in Freiburg, Germany

Therefore the test consists of 3 phases:

1. The system is bleached, no additional glare protection available 30 min pause for the switching of the glazing


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2. The system is coloured, no additional glare protection available 3. The system is coloured, additional white venetian blinds as glare protection accessible for the subjects

During each phase, the subjects perform a test and have to answer a questionnaire. The tests for the three phases are identical in the degree of difficulty, but are not exactly the same otherwise learning effects would influence the results. The results of each phase are collected separately. The evaluation of the results is done with the statistical software “SPSS”. Set up of unoccupied test rooms

4.4.3 Inside view of the test room, a TFT computer screen is used for the tests

The test rooms are located on the room of the building of the Fraunhofer ISE. Due to this location, quite no obstruction situation can occur. Only in the northeast orientation, some exhaust tubes of the clean room facility obstruct the rooms. But this orientation play no role, since the tests took place in the late morning and early afternoon. Since the rooms are fully rotatable, the tests can be done at similar sun heights, only the view changes between the subjects.

To keep the temperature influence as small as possible, the test room has an air conditioner, which holds the temperature between 22-24°C. Due to a very stable weather situation in April 2003, most of the performed tests could be used for the evaluation. All the tests are done during sunny conditions.

3.65 m 3.65 m

At the users eye position, a high dynamic luminance camera is placed in order to monitor the window luminance.

.78 m

The working desk is placed near the façade with a 0.7 m distance to the back wall (see pictures). The flat screen of the test computer is placed in 1.5 m distance to the façade.

Reference room

Storing space

Sw itchabel facade

The illuminance values are recorded continuously in 30 s steps during the entire test (about 2 hours). They are evaluated afterwards to guarantee more or less constant ambient conditions. Parallel to them, the data acquisition system records also the outdoor conditions (vertical illuminance in façade plane, direct and diffuse radiation, horizontal illuminance).

Sw itchabel facade

The façade layout is similar to the reference room description of the simulations. The test room layout can be seen in figure 4.4.4. The electrolyzer is placed in the opaque part of the façade and is fully integrated. The control unit and control computer is placed in a small storage room between the two test rooms, where also the measurement acquisition system is located. In the reference room, 5 horizontal illuminance sensors are placed in the middle axis of the room in desk 4.4.3 Inside view of the reference room: Identical furniture and screen position height (80cm). In addition to this, on the workplace (horizontal), on the than in the test room computer screen (vertical), behind the window (vertical) and two wall positions(vertical) are illuminance sensors located. These sensors re 4.80 m placed in both rooms to ensure to have the same conditions on both rooms.

Data aquis.

Test room

4.4.4 Layout of the rotatable test rooms

Description of tests and design of questionnaire To get reliable data of the users assessments, it is necessary, that the subjects have to perform tests, which are not too easy and which are close to usual office work. Therefore it was decided to use three different tasks for one test wave, which cover the three most frequent (visual) working


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tasks in offices: 1. Paper reading 2. Text typing 3. Text reading on computer screen The three tasks would offer to evaluate them itself like “performance of typing”. But this was not the scope of the project. These three tasks are just used to have an office like task for the subjects. Since the switchable glazing is an upcoming technology, we decided to us flat screen monitors as computer displays. Many problems like reflections and veiling glare is dramatically reduced with this display technology. 4.4.5 View to window and monitor in the test room, façade is in coloured mode

4.3.1.2 Reading task 100000

10000

Illuminance [lux]

The Reading Task was a simple text on a sheet of paper, placed horizontally on the table. The text is easy to read and contains also some pictures. The pictures are important for the evaluation of the colour rendering.

1000

100

10

Phase 1: Bleached No glare prot.

Switchin g

Phase 2: Colored no glare prot.

Phase 3: Colored with blinds

Vertical illuminance outside Desk illuminance test room

4.3.1.3 Typing task

1 12:15

12:30

12:45

13:00 13:15 local time

13:30

13:45

14:00

The Typing Task used, from NRC (National Research Council, Canada), 4.4.6 An example of the illuminance will measure the speed and accuracy with which the subject is able to situation on the workplace during one retype a given text. It is designed to resemble the typing proficiency test test. All the tests are done during sunny weather conditions required of applicants seeking placement at agencies for office temporaries. In the upper part of the screen, the subject sees a given text, which has to be retyped in the lower part. In the swift tests, we used black letters (12pt) on a white background.

Letter-search task To increase the degree of difficulty of the visual tasks of the subjects, it has been decided to use an ISO standard test procedure that measures the effectiveness of the transfer of visual information in terms of subjects search performance for targets embedded in alphanumerics on a screen. Effective in this context means that the user is able to detect and recognize the visual targets accurately, quickly and without visual discomfort. The task is to find a the specific letter (e.g. A) in the text and count the occurrence. This test is repeated 5 times with other pseudo-text samples on different positions.

4.3.1.4 Questionnaire The questionnaire is split up in 5 sections: 1. personal items like age, glasses, mood 2. personal preferences (e.g. advantages and disadvantages of windows, importance of windows…) 3. questions about the lighting situation on the workplace directly after a test (This question section appears 3 times, always after a test 4. questions about the lighting situations in the room during the 3 tests and control issues


0 to 1 to 2 to 3 3.5 to 5 to 6 to 7

not at all -0 + ++ extremely

4.4.7 An example of the typing task used from NRC, which measures the speed and accuracy of the subject retyping a given text. Upper part: given text. Lower part: typed text. WhwNdzo zltpVY 1CCAe kDw he t3 TkW3rm8U ya BpE O2B L8Y A5 She PQtb 90DViRCDG 1H pSM yEqZz 6F jyA3 sATQesa ANUU VLH Ou1p2JBE vbR l1Y5rVr SA9mr DmPETLV 2uO2 7phnFd2oyT 83ee zKo8h KyiTJgAL vXMu 6Kugm 3ElkxsOWhCK1FTMA T6 LuGF5 ad HsicT H0jkHv ssAq U8Q 8dW rmrtfGqh HCsnGdYIMQEITS fo o1 XVw6 2VogMFo6 PH uJD3c DXj8 yW 5LN 6Bv0 fGPhdZ Cn x9gUiaH3 fySFoauaxj UeK bKQz 2uZa MmnCN 4t HT3OFuMUSo piq1uUh8tdRbK1Tn Ez 33Q 6w fvVR 7B gyz Ns5 5Ami 7T5k 6bc2 ZHl fJmDO GwJ9 ECKYm Xob3m t9 SU ZR e1 3lFg 1wc j4w nToPDF RCUb nyMHs rMI0oizFL8dx a2Z sD AK5R1 Q8jiI wBeeA L2Rz0

4.4.8 An example of the pseudo-text which will be displayed as a block of characters. The subject’s task is to scan the text and identify the presence of the target character (e..g. letter A).

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5. general questions about preferences, colour rendering

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30 % 25 %

The design of the questions is based on the experience of the IEA-Task 21 questionnaires.

20 % 15 % 10 % 5%

Results

0% 23

24

25

26

4.3.1.5 General items During the tests in April 2003, we had about 27 valid tests with subjects. The subjects are very homogeneous in terms of age (see graph) and profession (students, scientists (not on lighting) and secretaries). 66 % don’t need to wear glasses or contact lenses (37% glasses, 7% contact lenses).93 % of the subjects stated, that an window in a room is important for them. The question about the preferred light type is shown in following graph. 78% prefer to have daylight alone, none electric lighting alone.

27

28

29

30

35

age [years]

4.4.9 Age distribution of the subjects 90 % 78 %

80 % 70 % 60 % 50 % 40 % 30 % 20 %

15 % 7%

10 %

0% 0% no preference

4.3.1.6 Acceptance

Only 45% of those people, who prefer the conventional system, are disturbed by the colour of the glazing. The correlation factor for these two questions is about .54, which is rather low. These values must be noticed with care, because the number of the test group (=people who prefer the conventional system) is somewhat small (9) to have really reliable data (Minimum should be 15). But this result gives a tendency, that there are other factors important, which are not covered yet by the questionnaire.

50 %

4.3.1.8 Glare limit In national regulations, many different glare limits of the façade are mentioned. Those limits lie in-between 400 and 4000 cd/m², depending on country and monitor type. Since there are only a few investigations with new flat screen monitors available, this aspect is evaluated here, too.


If you would have the possibility to choose the glazing type of your own office, which one would you choose? 48 %

40 % 33 % 30 % 19 %

20 % 10 % 0% Convential Glazing + Glare protection

Switchable Glazing alone

Switchable Glazing + additional glare protection

4.4.11 Acceptance of the system: Personal preference of shading systems

Bothered by glare through window (reading, typing, searching task) 7.0 6.0 5.0 4.0

Bleached mode, no glare protection Colored mode, no glare protection Colored mode with add. glare protection 3.98

3.0 1.84

2.0

1.22

1.0 0.0

4.4.12 Glare rating (bothering) for different façade states and all test tasks(reading, writing and search task). The coloured mode reduces dramatically the glare effects of the window. Only indirect glare from the sun or direct glare from the sky has been under investigation in this test. Due to the high sun position, the rays from the sun never could hit the subject’s eye Degree of glare (reading, typing, searching task) 5.0

4.0 Degree of glare

One of the main reasons, why the acceptance is so high is the fact, that the visual comfort during tests was very high. One major item is, that due to the high sun position during the tests, the sun could never hit the subject’s eye directly. Therefore only indirect glare effects from the sun or direct glare from the sky could disturb the subjects. Obviously these effects can be effectively reduced by using a switchable glazing (see figure 4.4.12). Bothering is one aspect. But acceptance of glare situations another. E.g. a situation could be bothering, but also accepted because of the advantage of the view to the outside. To find this difference, a second question regarding glare is evaluated in following graph. One can see, that the general tendency is the same, but also the transparent mode with even an higher average luminance of the façade is just acceptable.

electric lighting

60 %

In a succeeding study, one should ask about the reasons for choosing a conventional system.

4.3.1.7 Glare reduction

combination of daylight and electric lighting

4.4.10 Preference of lighting type

Bothering

The acceptance of the switchable façade is very high: 2/3 of the subjects would like to have such a system at their own workplace, 1/3 would prefer a conventional system like DGU and venetian blinds. This result is really remarkable, because the acceptance is very high, although it is a new technology and people usually are suspicious to new technologies, which influence their daily work. But even having a high acceptance, there is 1/3 of the people who would prefer a conventional system. Going more into detail one can find, that it is probably not the colour rendering, which is the reason for the 33% to choose another system.

daylight

Bleached mode, no glare protection Colored mode, no glare protection Colored mode with add. glare protection 3.10

3.0

2.0

1.65 1.22

1.0

0.0

4.4.13 Degree of glare (acceptance) for different façade states and all test tasks(reading, writing and search task).

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We monitored the average window luminance of the user’s position with a luminance camera equipped with a fish eye lens. The frequency of making the luminance pictures is one every two minutes. The average luminance values of the four windows is averaged over the duration time of each task of the test. It could be shown that this value is correlated very well to the degree of glare of the letter search test. Evaluating the results (see figure 3.4.13), a luminance limit for the facade of 1000 or 2000 cd/m² as postulated in regulations is too low for our test case. This limit overestimates the user’s reaction in at least 40% of the cases. A limit between 4000 and 6000 seems to be more appropriate, at least for this kind of façade arrangement (size and position of the glazing).

4.3.1.9 Control issues In another set of questions, some two control issues are investigated: 1. Do the people want to have an automatic control of the glazing?

4.4.13 Example of a luminance measurement in the reference room during the test. Within the evaluation software of the camera, 4 window objects have been defined to determine the average window luminance.

2. If there is an automatic control, how important is it for the people to have influence on the control (manual override)? 10000

4.3.1.10

Colour-rendering

Average Facade Luminance [cd/m²]

Wrong limit in 40% of the cases

41% of the subjects would prefer full manual control, but 71% want to have at least the manual override function (see following graphs).

Another important item to assess is the colour-rendering item. Spectral measurements and colour evaluation showed, that there are for the GC system high colour changes in the coloured mode and the colour rendering could be a problem, just evaluating the laboratory values. But the question is, how do people react to the colour change. As described before, the tests are office like and are also dealing with some photographs and work on the computer screen.

9000 8000 Overestimation 7000 6000 5000 4000 3000 2000 1000

Underestimation

0 Not perceptible

Just Perceptible Just Acceptable

Just Just Intolerable Uncomfortable

4.4.14 Correlation between average façade luminance and glare scale. The 2000 cd/m² overestimates the reaction of the users in 40% of the cases

Average Facade Luminance [cd/m²]

10000

For the bleached mode, 93% of the subjects find, that the colour is neutral. Of course, this changes, if the glazing is in coloured mode. But even in that state, 30% of the subjects still feel, that the colour is neutral. Only 15% of the people are really disturbed by the colour. 70% of the people are not disturbed by the colour.

9000 8000 7000

Overestimation

6000 5000

Wrong limit in 11% of the cases 4000 3000 2000

Underestimation

1000 0

Just Just Intolerable Uncomfortabl

Not perceptible Just Perceptible Just Acceptable

Conclusions

4.4.15 Correlation between average

•

façade luminance and glare scale. The short-term tests showed, that the switchable glazing has a Between 4000 and 6000 cd/m², the limit high acceptance by the people. People, who prefer a conventional correlates much better system are not consistently bothered by the colour rendering.

•

For those cases, where the sun can’t hit directly the eye of the people, the GC system can act also very efficient as glare protection system, even if the people rate the combination with venetian blinds slightly better. Although we have made no tests with situations, where the sun could hit the subjects eye, it is obvious due to the high luminance of the sun, that in those cases an additional glare protection is needed.

40 % 35 %

37 % How important is influence on automatic control of switchable glazing for you?

30 % 25 %

22 %

20 % 15 %

14 %

4%

5%

1%

A glare limit of the façade luminance of 2000 cd/m² seems to be too low. A limit between 4000 and 6000 cd/m² correlates more to the user’s reaction for this kind of facade arrangement.

•

People would accept an automatic control, if they have the possibility to override it.

•

Most of the people recognize the colour change, but are not


2%

0% not at all

•

12 %

10 %

++

+

o

-

--

very much

4.4.16 Importance of manual override

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disturbed by it.

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100 %

93 %

Please assess the color rendering in the room

90 % 80 % 70 % 60 %

colored mode bleached mode

50 % 40 % 30 % 20 % 10 %

30 %

26 % 15 %

11 %

4%

0% disturbing

0% --

4% -

7% 0%

7% 0%

0% recognizable

+

4%

++

neutral

4.4.17 Assessment of the colour rendering

4.4

References

48. Tenner A.D., Zonneveldt L., “Switchable Facades and Visual Comfort”, submitted to Right Light 5, Nice, May 29-31, 2002. 49. De Myttenaere K., “Practical integration of electrochromic glazing in the office room in Eindhoven”, in WP3 - SWIFT Project, 2001.

4.5

Iconography

All the pictures and drawings included in the text are made by the authors, that is from Sergio Altomonte (UCL) for chapter 4.1, from Michele Zinzi (ENEA) for chapter 4.2, and from Jan Wienold (ISE) for chpater 4.3 except:

- Images n° 4.1.1, 4.1.2, 4.1.3, 4.1.4, 4.1.5a, 4.1.5b, 4.1.5c, 4.1.5d, 4.1.6 are courtesy of José Flémal (UCL).


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5 Building integration and simulation results 5.1

The reference office

In order to investigate the impact of switchable glazing on visual conditions and on energy consumption in working environments, computer simulation often is used. Because energy effects are very difficult to measure computer simulations provide an economic mean to gain insight in dependencies and to develop guidelines for future application of switchable glazing. To find out the overall energy impact of the switchable glazing, it is necessary to know about the daylight and the thermal behaviour. Since the daylight influences the amount of lighting energy and therefore also the internal loads, both simulations must be coupled. We have defined a reference office for simulation of lighting and energy in 54,51 cooperation with IEA Task 27 and IEA Task 31 . The advantage of this reference is that as more results of simulations become available the results can be compared and analysed.

0.10 m

0.50 m

1.10 m 0.40 m

1.20 m

2.70 m

1.20 m 0.10 m

0.80 m 0.15 m

0.15 m

3.50 m

5.1 Façade lay-out of the reference office 5.40 0.75

0.75

0.75

1.05

1.00

1.50

3.60 As for computer work places the glare from the windows has to be limited a glare protection device in addition to the switchable facade has been 2.55 defined and used in simulations. The reason is that switchable glazings might control the glare from the diffuse sky to a reasonable limit, but for 1.50 direct sun a clear glazing never can reduce the sun luminosity sufficiently and provide some daylight and vision at the same time. Compare the sun 5.2 Layout of the reference office with glasses for the solar eclipse! In order to allow a view through an internal workplace position. The two marked venitian blind has been chosen. positions have been chosen for the swift project. As representative climates for the simulation meteorological data sets from three locations have been chosen:

Stockholm

Brussels

Rome

5.2

Northern European climate, heating dominated Latitude 59.21° Yearly temperature average 6.6 °C 2 Yearly global irradiation sum 982 kWh/m Central European climate Latitude 50.48° Yearly temperature average 10.2 °C 2 Yearly global irradiation sum 959 kWh/m Southern European climate, cooling dominated Latitude 41.28° Yearly temperature average 14.6 °C 2 Yearly global irradiation sum 1556 kWh/m

5.3 Visualisation of the blinds in 15° position for the standard window size

Simulation tools and methodology

The simulation of energy performance für buildings with a dynamic envelope changing the solar energy and light transmission characteristics in response to comfort parameters like room temperature and visual glare has to consider lighting, cooling and heating energy consumption. Therefore several tools are needed: - a daylight simulation to determine the glare and illumination levels - a tool determining lighting loads using illuminance levels and user requirements - a tool for thermal building simulation using the solar gain and artificial lighting loads for the determination of cooling and heating energy and the evolvement of room temperatures For daylighting the Radiance tool capable of lighting calculations based on 56 physical properties of materials in complex geometries was chosen . Radiance was only used for numerical simulations. In order to perform Contract ENK6-CT1999-SWIFT

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simulations to calculate lighting levels and other parameters such as 49, 50 energy for artificial lighting the DAYSIM tool is used. For building simulation one group used ESP-r 52 developed at the ESRU group of the University of Strathclyde in Glasgow . Another group used the 55 widely spread TRNSYS program . In all the programs specific component models have been used based on measurements, representing the visual, solar and thermal properties of the switchable facades. For four different conditions of the facade (coloured and bleached switchable glazings, blinds down and up) the desk illuminances and the average facade luminance for the occupants looking towards the facade was simulated and saved as hourly results in files. For electric lighting two control algorithms have been investigated, one simulating manual on/off-control, and the other dimming according to the specified illuminance level on the desk. Again this gave four different results depending on the facade conditions. Within the TRNSYS building simulation tool, the electric loads could be read in and the relevant value could be chosen dynamically during the simulation depending on the simulated controller signal, which could depend on irradiance, facade luminance and room temperature. For ESP-r, this was not possible, therefore the glazing was always controlled by the vertical irradiance onto the facade – something which is determined and cannot be changed by simulation results. For blind operation a manual user control was approximated. The main parameter for manual control algorithm is the façade luminance. When the user enters the room, the blinds are retracted. If direct sun hits the workplace or the eye, the blinds will be closed until this is not any more possible. Then, the façade luminance is checked. If it exceeds 5000 cd/m², the blinds will be closed until the façade luminance is below 5000 cd/m². The blinds will stay in that position, unless electric lighting is needed or the user leaves the room (lunch or evening).

Daylighting and artificial lighting

Simulations with a roller blind system as glare protection showed, that the glare protection control has a strong influence on the lighting energy. Especially the control rule “luminance reduction on the façade” leads to a higher electric energy consumption of the lighting the smaller the target value is. Of course, this general rule is valid for all glare protection systems. But the roller blind system was modelled in the first stage as “binary” system, what means, that is has only two modes: Closed or open. And since the façade luminance is very often above target values of 400-5000 cd/m², the system would be closed most of the time and the lights are extremely often switched on. Internal venetian blinds as glare protection have many advantages: They can cut the direct view connection to the sun without loosing the view contact to the outside. On the other hand, they can be controlled quasi continuously to reduce the façade luminance to the wished setting, without “over reducing” the façade luminance.

2500

=3000 cd/m²

500

Type: v001: reference, Brussels bin level electric lighting: 300 lux 0 0

100

200

300

400

500

600

700

Level of switching [W/m²]

5.4 Influence of the glare protection target value and the switch level on lighting energy (hours light on) for the manual control. The front and back lighting installation is shown separately

But even when using an optimised glare protection system, its operation strongly influences the energy consumption of the electric lighting. The main parameter is the target luminance limit to which the façade is “dimmed” down. Looking onto the European standards and on actual research in that field, different values are in discussion. The lowest value, Contract ENK6-CT1999-SWIFT

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which can be found is 400 cd /m². But this value was determined by the use of old screens with bad antireflective coatings and negative contrast (black background, white letters). On the other hand for modern TFT 53 screens with a good antireflective surface up to 4000 cd/m² is mentioned . Within the SWIFT user assessments in test rooms, we found 5000 cd/m² as a maximum acceptable average luminance of the façade. But these different values of course lead to different energy consumption for the lighting. Regardless of the control strategy of the glazing, these different target glare values lead to a difference of about 40% of the electric lighting (e.g. for the Brussels climate, standard office, south orientation)! In following graph, the influence on the lighting is shown exemplarily for one variant.

5.4

Optimisation of the control strategy specific primary energy demand [kWh/(m2a)]

Two different optimisation investigations were performed. One using the flexible TRNSYS program with different control strategies. This investigation was restricted to a roller blind glare protection system and a the standard reference office configuration with 30% glazing fraction in the facade. The second study investigated more options concerning the reference office, and used the Venetian blinds with different tilt angles of the lamellae.

70

heating

40 30 20 10 0 300 W/m2

4000 cd

24 °C

irradiance

luminance

room temperature

switching criteria

5.5 Primary energy consumption (PEfactors for Germany) for different optimized control strategies (switching according to facade irradiance, to window luminance or to room temperature) gaschromic system, Central Europe, 30% glazing fraction 45.0

Stockholm, South orientation Gaschromic system

40.0

39.2

specific end energy demand [kwh/m²]

Summer Lighting 35.0

4.9

Summer Cooling

30.5

30.1

30.0

31.1 29.4 7.2

25.0 19.9

19.2

20.0

17.7

9.7

9.3

8.7

20.8

20.7

20.7

0

50

18.6

18.1

34.3 15.0

10.5

9.8

7.8

5.8

6.8

23.9 10.0 5.0

9.4

9.4

9.9

11.3

0

100

300

400

12.8

0.0 500

100

300

500

switch point [W/m²] 30% glazing

60% glazing

5.6 The effect of the glazing area on the optimum switch point. All data are for the south orientation in Stockholm and gaschromic window system 35.0

Brussels, South orientation Electrochromic system 28.9

30.0 specific end energy demand [kwh/m²]

Using the ESP-r program the optimisation concentrated on the control strategy using the vertical irradiance as control value. For both systems the climate has a minor influence on the optimum switchpoint. On the other hand, for higher glazing area the optimum switchpoint is shifted significantly towards lower values, which means the glazings are much more often in the coloured state. For the standard window size of 30%, about 300 W/m² is an optimum for gasochromic, whereas for electrochromic, the optimum switchpoint is always beyond 500 W/m², which means not to switch! For the large window size (60%), about 100 W/m² is the optimum switchpoint for both systems in all climates.

lighting

50

57,58

It could be shown that concerning primary energy consumption, a control with respect to room temperature (with 2 K switchpoint below the cooling setpoint) produced the best overall energy savings (lighting, colling and heating). However, even with a simple seasonal switching strategy the energy consumption is only 5-10% higher than the optimized control. This result is somewhat specific to the primary energy factors, of course. They are different for countries with high and low fossil fuel contributions to electricity production. However, the change may be in absulte numbers, but not in theoverall tendency, as the optimisation of controls mainly changes the contribution of cooling and lighting on the energy demand, and these two are both based on electricity.

cooling

60

27.4

Summer Lighting 25.0

26.2

9.4 20.0

26.3

Summer Cooling 18.5

17.5

16.5

16.4

7.7

6.3

8.3

7.4

18.0

17.9

18.9

0

100

26.9 4.5 6.8

15.0 10.1

9.2

10.0

5.0

8.4

8.4

8.8

0

100

300

24.4 20.2

10.1

0.0 500

200

300

500

switch point [W/m²] 30% glazing

60% glazing

5.7 The effect of the glazing area on the optimum switch point. All data are for the south orientation in Brussels and electrochromic window system


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Energy savings

Simulating the heating and cooling energy demand using the program TRNSYS resulted in low energy consumption when compared to the case of low-e coated heat mirror or solar protection glazings with corresponding high or low total solar energy transmittance. The following table gives an example of energy consumption values (referenced to South and North offices and adjacent corridor floor area) Table:

Example for annual heating and cooling energy demand for different glazing options (for 30% glazing fraction)

Glazing system comparison; 60% glazing 120 ref Specific summer end energy use [kWh/m² floor area]

5.5

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GC

EC

100 80 60 40 20 0 Brussels

Rome

Stockholm

5.8 The specific summer end energy use for the three different glazing systems compared for the climates with 60% glazing. For the GC and EC systems, the situations are used with optimum switch value.

2

HM: Heat mirror double glazing (U=1.3 W/m K, g=62%) 2

SC: Solar control double glazing (U=1.1 W/m K, g=33%) 2

GC : Gasochromic glazing (U=0.9 W/m K, g=48%/18%) 2

EC: Electrochromic glazing (U=1.1 W/m K, g=40%/15%) 2

Heating energy qH [kWh/m a] HM 3.7 16.6 33.8

SC 5.5 20.3 39.4

EC 5.8 19.9 37.9

GC 4.9 17.2 33.1

2

Cooling energy qC [kWh/m a] Rome Brussels Stockholm

HM 45.5 16.3 18.8

SC 24.2 6.8 7.3

EC 14.1 3.0 2.6

GC 15.2 3.4 3.1

It is also obvious that lighting control has an effect on the energy consumption. Dimmed systems have the higher potential of reducing the energy demand for lighting than manual on-/off-control. From an analysis of the two workplace one can conclude that typically the optimum switchpoint ist reached, when the daylight autonomy for the front workplace has reached the maximum. The rear part in any case seems to need artificial lighting. Daylight autonomy is the percentage of working hours, when daylight alone is sufficient (>=300 lux) to light the desk.

Lighting control 30 20% glazing Specific summer end energy use [kWh/m² floor area]

Rome Brussels Stockholm

25

30% glazing 60% glazing

20

15

10

5

0 manual

daylight responsive

5.9 The effect of lighting control on the specific summer end energy use with changing glazing area for the Brussels climate

It is not surprising, that simulations showed for the offices in all climates a need for solar protection, which effectively can be provided by switchable glazings, and as a consequence energy savings when compared to static low-e coated windows. Of course, effective external shading devices, if operated in cut-off position, would reach similarly low cooling demand, whereas internal devices with generally less solar protection would reach slightly larger cooling demand. The essence is, that switchable facades can reach as low cooling demand as facades with external shading devices, and a heating demand similar to a heat mirror glazing without shading. In addition the advantages of the switchable glazings are •

Permanent view through the window

•

No restrictions to operation because of wind

•

No mechanical device

•

No external structure in front of glazed façade (appearance of building)

As the cooling energy demand is small when the switchable façades are investigated, one might be interested whether natural or passive cooling could be sufficient to avoid overheating of the building. This is certainly not Contract ENK6-CT1999-SWIFT

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the case for Rome. In extreme periods the ambient temperature is very high even at night time. Thus cooling by nighttime ventilation is not effective. However, first simple strategies of increasing nighttime ventilation in Brussels or Stockholm reduced the number of overheating hours substantially with only a few hours above 27°C (for comparison: double low-e glazing without night time cooling around 700 hours above 27°C). For a real building project passive cooling options should be optimized of course, e.g. by increasing accessible ceiling mass, or by using earth-to-air-heat exchangers.

5.6

Peak load reductions

Using switchable facade technology with a building envelope reacting to the environmental factors, especially irradiation by the sun is able to smoothen out the unwanted high solar gain peaks. Therefore cooling peak loads, which are the indicators for the required maximum installed cooling power, is connected intimately to total solar energy transmittance g of the glazings – when g can be reduced (by switching) there is a possibility to reduce system size and investment costs. However, excessive outdoor temperature also contributes to the cooling load in the room: Due to the large temperature difference there is a heat gain to the room. As simulations have shown, this is especially true for the hot climate Rome. Therefore lowering the U-value of the glazing is beneficial for cooling loads in summer. Of course, a low U-value is the main factor for reducing heating loads during the winter. These qualitative reasoning could be substantiated quantitatively by 2 simulation. As the U-values of the electrochromic glazing (U=1.1 W/m K) 2 and the gasochromic glazing (U=0.9 W/m K) were lower than the one for 2 the reference glazing (U=1.3 W/m K), the maximum peak heating power was reduced to some extent in the heating dominated climates. However, the effect on maximum peak cooling load was remarkable. The reduction depends to some extent on climate and of course glazing fraction in the facade. The reduction ranged for 30% glazing fraction between 20% and 60% reduction of peak power. Interesting enough, the reduction is most pronounced for Northern Europe, and smallest for Southern Europe. This reflects the fact, that cooling loads in the North are dominated by solar, whereas in the South they are to a large extent due to high ambient temperatures. When the glazing sizes are increased, the relative reduction in peak power ios even more pronounced.

5.7

References

49. C. F. Reinhart, 0. Walkenhorst, Dynamic RADIANCE-based Daylight Simulations for a full-scale Test Office with outer Venetian Blinds, Energy & Buildings, Vol. 33 pp/ 683-697, 2001


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50. C. F. Reinhart, S. Herkel, The Simulation of Annual Daylight Illuminance Distributions- A state of the art comparison of six RADIANCE based methods, Energy & Buildings, Vol. 32 pp. 167-187, 2000; see also http://irc.nrccnrc.gc.ca/ie/light/daysim.html 51. Dijk, Dick van (2001) Reference office for thermal, solar and lighting Calculations, Version 1.00, September 27 Dijk, Dick van (2002) Draft Addendum to Reference office for thermal, solar and lighting calculations, Version 1.00add, April 29 52. ESP-r (2002), Environmental Systems Performance, Version 9 Series – “Dynamic thermal simulation environment for the analysis of energy and mass flows and environmental control systems”, © The University of Strathclyde 1990, Glasgow 53. Gall D., Vandahl C., Jordanow W., Jordanowa S. (2000) „Tageslicht und künstliche Beleuchtung: Bewertung von Lichtschutzeinrichtungen“, Schriftenreihe der Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, Fb 882, Dortmund/Berlin 2000 54. IEA SHC TASK 27 Performance of solar façade components – see http://www.iea-shc-task27.org/ and http://www.iea-shc.org/task28/index.html 55. S.A. Klein, W.A. Beckman (1976), ASHRAE Transactions 82, TRNSYS – A Transient System Simulation Program 56. Ward, Greg Larson and Rob Shakespeare (1998) Rendering with Radiance, Morgan Kaufmann, San Francisco 57. W. J. Platzer (2003) Eigenschaften und Einsatzkriterien für optisch schaltbare Fassaden bei Bürogebäuden, 13. Symposium Thermische Solarenergie, Kloster Banz, Staffelstein, 14th – 16th May 2003 58. W. J. Platzer (2003) Switchable Facade Technology – Energy Efficient Office Buildings with Smart Facades, Solar World Congress 2003, Göteborg, 14.-19.6.2003

5.8

Iconography

- All the pictures and drawings included in the text are made by the authors, Jan Wienold (ISE) and Werner Platzer (ISE)


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Annex: Technical Guidelines Part II: Technical Guidelines 1 Introduction The following technical guidelines are intended to show anyone involved in building construction which specific aspects must be taken into consideration when dealing with switchable glazing in all phases of a building’s construction. This document is therefore directed towards both architects in the preplanning stage, planners involved in technical installation, detail and implementation planners and finally those carrying out the actual work. This document cannot and does not intend to be a comprehensive instruction manual for planning and installing switchable glazing, as such a product has to be tailormade to the requirements of the building, for example as with conventional sun protection. The diverse possibilities for use require careful and building-oriented planning and solutions. For optimum solutions it is therefore advisable to enlist at an early stage the specialist advice of the system provider. This advice is given by specially trained personnel.

2 Gasochromic and electrochromic system components 2.1

Gasochromic system and its components Interpane's gasochromic glazing is a form of switchable glazing, which allows the transmission of light and solar energy to be varied in accordance with the prevailing weather conditions. During hot weather, the transmittance is reduced to prevent overheating, whereas the transmittance is switched to the higher value during cold periods, allowing solar gains to be used effectively for heating. Gasochromic panes are coloured and decoloured by passing low concentrations of a reactive gas through the gap between the panes. This gas reacts with a special coating applied on one pane surface facing the gas-filled cavity. This is colourless when in the bleached state and therefore transparent. In the coloured state this layer becomes blue in colour. At the same time it is not only the actual colour of the insulating glass which changes. It also alters its physical properties in respect to light transmitting capacity and overall energy transmittance. As this is a maintenance-free system, the gas required is both produced and circulated within the system in a closed circuit. The system thus consists of the following: -

Insulating glazing unit including connections for the gas supply

-

Gas supply unit

-

Connecting pipes

-

Electronic control unit

The following diagram shows the schematic structure of the gasochromic system:


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Gasochromic glazing unit Pane

Pipes

Gas supply unit

Electronic control unit

Electronical control unit

Figure 0-1: Schematic structure of the gasochromic system

The optically active component of a gasochromic IGU is a film of tungsten oxide (WO3), less than 1 µm thick, which is coated with a thin film of a catalyst. It is located on the inner surface of the outer pane of a triple IGU. When the gasochromic film is exposed to a low concentration of hydrogen (well below the combustion limit of 3 %) in a carrier gas of argon or nitrogen, it colours blue, reducing the visible and total solar energy transmittance values. On exposure to a low concentration of oxygen, it bleaches to the original transparent state. The gas mixture is introduced into the cavity between the outer and middle panes of a triple IGU. The second gas-filled cavity and third pane, which has a low-emissivity coating, ensure that the IGU has good thermal insulating properties (low U value).


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Figure 0-2: Gasochromic triple glazing

Clear visibility from inside to outside is retained in all switching states. In contrast to conventional, external shading systems, gasochromic glazing can also be used in the upper storeys of high-rise buildings. The gas supply unit consists of an electrolyser and a pump, which is connected by pipes to the window in a closed-loop configuration. Ideally, the gas supply unit is integrated into the external building facade. One gas supply unit is able to provide sufficient gas to 2 switch 10 m of gasochromic glazing. Switching occurs within 2 to 10 minutes. The control unit allows both manual and automatic control. Integration into a bus system allows the glazing to be switched to optimise lighting conditions, thermal comfort and/or building energy consumption. The control unit can be mounted wherever it is convenient. Pilot production of gasochromic IGU's with a maximum area of 1.5 m x 1.8 m started in 2002.

2.2

Electrochromic system and its components The electrochromic glazing system from FLABEG is an alternative to the gaschromic mechanism described above, and is also used to control the light and energy flow from the outside to the inside of buildings. Electrochromic windows from FLABEG are based on thin film tungsten oxide layers, which can be coloured and bleached reversibly by applying an electrical potential (voltage control). In order to apply an electrical voltage to the abovementioned coating, electrical cables are passed through the pane edge seal and connected to the layer. The electrochromic system thus consists of: -

Insulating glazing unit including electrical cables with plug

-

Electrical cables for supply and control

-

Glass unit controller

-

Group control unit

The following diagram shows the schematic structure of the electrochromic system:


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Electrochromic Pane unit glazing

Electrical cables for supply and control

Glass unit controller

Group control unit

Figure 0-3: Schematic structure of the electrochromic system

The electrochromic window from FLABEG is a double glazed unit consisting of a laminated electrochromic glass pane and a standard glass pane which is coated with a low-e-layer to achieve thermal insulating behaviour. The laminated electrochromic pane is built from two TCO-coated glass panes (TCO: transparent conductive oxide), which are coated with tungsten oxide (on one pane) and with a mixed metal oxide (on the other pane). The glass panes are laminated together with a lithium conductive polymer foil. The layer with the mixed metal oxide is the so-called counter-electrode and can consist of cerium, vanadium, or titanium oxide. This structure is shown in the following diagram.

sealing glass transparent conductive oxide tungsten oxide coating lithium conducting polymer counter-electrode transparent conductive oxide glass

Figure 0-4: Layer structure of electrochromic functional unit The following picture shows schematically the construction of an electrochromic double glazed unit. In a building instalation, the electrochromic pane is oriented toward the outside, whereas the third glass panewith the low-e-coating faces the inside. The spacer


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and the sealing materials are commercially available on the DGU-market and can be used here as in normal double glazed window systems.

EC-laminated glass 9 mm

Gas filling / spacer 16 mm

Glass pane with low-e coating 4 mm

Wirering to control unit

Figure 0-5: Electrochromic double glazing

Electrochromic panes from FLABEG can be switched to transmittance values from 50 % (bleached state) to 15 % (coloured state) by applying low voltages (about 3V). The windows can be produced in a range of sizes,from 40 x 40 cm to 120 x 200 cm, using a pilot plant at FLABEG subsidiary at Furth im Wald with a yearly capacity of about 20.000 qm.

Figure 0-6: User controls for electrochromic windows indicating state 1 (bleached) and state 5 (fully coloured)

Each electrochromic window can be switched between five states by simply pressing a button. It is also possible to control many ec-panes simultaneously with a group controller, which can switch up to 32 panes in one action.


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3 Profile systems for windows and facades As already described in the previous chapter, switchable glazing not only consists of the glazing itself but also several components which enable the glazing to switch. Electrical cables or supply pipes are introduced to the pane. Among other things, these panes cannot therefore be treated and installed like conventional static glazing. The choice of window or facade system plays an important role when employing switchable glazing. The following chapter discusses the factors that must be considered when choosing the system. At this point the two basic options for installing insulating glass in buildings will be revealed in order to give a better understanding of the problems involved.

3.1

Window designs If smallish individual surfaces are to be glazed, a window design consisting of frame and possibly casement frame is generally used. The casement frame is required if the glazing is to be opened. The characteristic feature of such a design is the glazing bead applied from the room side. The glass is therefore generally fitted from the room side with this window design. Several hundred profile systems each with their own design features are available on the market. They differ in the material and cross-section of the profiles. In order to explain this more clearly, 3 different systems are shown in the following:

Figure 0-7: Aluminium TKI window system


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Figure 0-8: Wood/Aluminium window design

Figure 0-9

Plastic window

On account of the obvious and completely different form of the frames, it is not possible for window designers to recommend a common design or type for use in combination with switchable glazing. This does not mean that it is not possible to use switchable glazing in window designs. This is perfectly possible and does not necessarily require a great deal of effort and expense. The important thing with this type of design is simply that an agreement has to be reached between the glass supplier and the system provider or handler so that the cabling and connections can be individually worked out as regards specific technical aspects for problem-free window functioning.


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3.2

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Facade designs In contrast to the window designs described above, the second basic type of glazing structure clearly reveals more standard features independent of the system provider and material used. With the so-called facade designs consisting of mullions and transoms the profile carrying the static equilibrium is generally fitted on the room side. The usual materials for these support profiles are wood, steel or aluminium. A system consisting of EPDM profiles arranged outwards is built onto this support profile, which serves as a mounting area for the glass. The glass is therefore fitted from outside in contrast to the window designs. Depending on the architectonic requirement, facade designs have a fairly distinctive holding bead on the external side, which is screwed onto the support profiles on the room side and which presses the glass clamped in this way onto the support profile. This design principle is common to all mullion-transom structures, as the following figures showing examples of the systems will make clear.

Figure 0-10 Wood façade


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Figure 0-11:Steel façade

Figure 0-12 Aluminium façade The following part of the guidelines dealing with protoype characterisitc data and project planning are intended to reveal the key features of a system consisting of switchable glazing, which you can thus take into consideration in the planning stage. They are in no way a substitute for specialist advice by glazing system providers. Owing to the wide variety of window designs on the one hand, and the essentially uniform nature of mulliontransom designs on the other, the following will only deal with the facade design as the usual construction type in buildings.


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4 Prototype data Within the SWIFT project several prototype glazings have been tested in the laboratory. These prototypes serve as a basis for further development of the final commercial systems. Results from the user evaluations, from the reliability testing and from performance studies have been used to optimize the glazings since. Thus the measured data which are given here as a guideline for the potential characteristic performance of switchable facade technology may not represent the final commercial products to a full extent. The data are given for the complete glazing systems with a heat resistance suitable for European climates, not only for the single functional unit. The details of the insulating glazing units are different for the electrochromic and the gasochromic systems. Visual transmittance τv, solar transmittance τe and total solar energy transmittance g have been determined for different switching conditions and incidence angles in the laboratory. For direct transmittance a large integrating sphere equipment has been used, for energy transmittance a solar calorimeter developed to a very high standard (Platzer, 2000). The U-value of the glazings were also determined with this device in the dark, non-irradiated mode.

4.1

Gasochromic glazing

4.1.1.1 Specifications of the IGU The following sequence describes the glass layers of the glazing from outside to inside. 4 mm 8 mm 4 mm 16 mm 4 mm

tempered float glass with gasochromic layer (coating on surface 2) Argon filled cavity with less than 2% colouring/bleaching gas tempered float glass Argon filled cavity tempered float glass with Iplus R low-e (coating on surface 5)

4.1.1.2 Measured properties The gasochromic unit, effectively a triple glazed unit with one low-e coating on position 5, 2 reaches U=0.9 W/(m K). Table 1: Gasochromic glazing data state

bleached

coloured


angle [°]

Interpane GC g

τv

τe

0

0.48

0.60

0.40

30

0.46

0.59

0.38

45

0.46

0.59

0.37

60

0.42

0.51

0.32

0

0.18

0.15

0.08

30

0.18

0.14

0.08

45

0.17

0.13

0.08

60

0.15

0.11

0.06

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4.2

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Electrochromic glazing

4.2.1.1 Specifications of the IGU The following sequence describes the glass layers of the glazing from outside to inside. 9 mm 16 mm 4 mm

float glass laminate sandwiching electrochromic constituents Argon filled cavity float glass with Optitherm S low-e (coating on surface 3)

4.2.1.2 Measured properties 2

The electrochromic double glazing reaches a value of U=1.1 W/(m K), comparable to a modern low-e double glazing. Table 2: Electrochromic glazing data state

bleached

coloured

4.3

angle [°]

Flabeg EC g

τv

τe

0

0.40

0.52

0.33

30

0.37

0.51

0.32

45

0.36

0.48

0.30

60

0.33

0.41

0.25

0

0.16

0.16

0.08

30

0.15

0.14

0.06

45

0.14

0.13

0.05

60

0.13

0.10

0.04

Prototype frames For the different test facades and building facades several adaptations of the facade layout had to be produced. In some cases like the test facades, a standard aluminum profile facade had to be changed for pipings and cables, to incorporate the special features of a switchable facade. In other cases for integration in an existing building the main facade stayed as it was. Therefore special solutions had to be found for integrating a facade system into an existing structure without changing the appearance of the building.


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Figure 0-13:Drawings for test cell facade, Freiburg The frame U-value Uf has been calculated using the profile section and the program THERM2.0 according to EN 10077. Also a linear thermal conductance has been determined. The following table gives the areas and U-values for the individual parts of the test cell facade as example. Part

area A [m2]

U [W/(m2K)]

Glazing

1.94

0.93

Panels

1.10

0.88

Electrolyser box

0.53

0.76

Frame

1.03

2.90

Total

4.60

Including the linear thermal transmittance of the glazing edge the overall U-value for the 2 complete test facade is 2.1 W/(m K). This is certainly due to the large frame area, which comes from the need of fitting experimental glazing sizes into a relatively small aperture of a test cell. In a real building project the overall thermal loss coefficient would be smaller.

5 Planning a project As with most technical components within a building, it is also important for the consequent optimum use and functioning of the switchable glazing to consider this in the early planning stage and include it in the choice and construction of the facade design. Two categories can be differentiated here. On the one hand the unalterable requirement of the glazing on the mullion-transom design, and one the other hand the requirements of the installation situation on the glazing.


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5.1

Page 91 of 99

Requirements for switchable facade frame profiles (both systems)

5.1.1.1 Formats The beginning of every design for a facade structure is characterised by the decision on dividing the facade areas into individual partial areas. As soon as the decision has been made to fit a facade with switchable glazing, it must be borne in mind that for every switchable unit, as with conventional sun protection, a minimum and maximum area size must be observed, which is dependent on manufacture. The current respective minimum and maximum dimensions must be requested from the system provider beforehand, as the dimensions are dependent on the current production systems. Model panes represent a special feature within the formats that can be manufactured. By this is understood every form of glass different from the square type. These model panes can basically be manufactured within certain limits. It is, however also necessary here to inquire about the development status with the system provider and ask about concrete individual cases so as to avoid problems in the switching of the model pane later on.

5.1.1.2 Pane edge seal As with all other normal types of insulating glazing, switchable glazing has a pane edge seal which provides a gas-tight seal separating the gap between the panes from the atmosphere outside the panes. To ensure durable tightness for this pane edge seal and hence a longer working life, it is important to note that the following conditions must be met when choosing a facade system:

1. As with all conventional types of insulating glazing, the sealants used are not permanently resistant to UV damage caused by sunlight. For permanent tightness it is therefore necessary for the pane sealing to be completely covered by the holding bead applied externally. A glass infill measurement of at least 16 mm all round is necessary. This measurement must be included in the format layout!

The following sketch serves as an explanation:

16

min. / max. Dimension

Figure 0-14: Glazing installation With several designs it may be necessary to use a sealant in direct contact with the pane edge seal. Although this is possible, it is however absolutely essential to carry out a test for the compatibility of this sealant with the sealant of the edge seal.


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2. It is also equally important for the durability of the edge seal to ventilate the glass rebate (compare figure above), so as to remove condensation in a reliable manner. This dehumidification of the glass rebate, which is also necessary for conventional insulating glass, is ensured if the rebate space below the glazing has at least a height of 5 mm.

5.1.1.3 Pipes and cables The key difference in the design requirements of switchable glazing in comparison to conventional glazing lies in the fact that switchable glazing is connected to a complete system with electrical cables or pipes. To accommodate these system components the facade system used must provide sufficient space for these to be connected to the individual panes. The most sensible method is to accommodate these cables or pipes in the cavity which is formed on the outside of the structure by using a screw + cover strip. The following reasons support such an arrangement: Operating safety The cavity protects the cables and pipes well against the effects of rain and snow and enhances the operating safety. Any humidity occurring is removed reliably and quickly. The adverse affects caused by humidity are less than in the rebate space itself. At the same time the ventilation of the rebate is not restricted by supply cables positioned in it and its functioning is not therefore impaired.

Building process In the building phase it is thus possible to fit the glass rapidly and independently of the necessary installation work and hence seal the building. The cables or pipes can therefore be fitted at a later period, while further construction work on the building can be carried out independently of the weather.

The following two diagrams show the arrangement described:

Gaschromic arrangement

Supply piping

Figure 0-15:Arrangement for gasochromic glazing


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Electrochromic arrangement

Control and supply cables

Figure 0-16: Electrochromic configuration

5.2

Project-specific requirements Depending on the building, facades are fitted on buildings in a different manner. As with conventional insulating glass, for switchable glazing the glass must also be designed in respect to statics and climate, depending on the type of installation. When designing the glass strengths of the switchable glazing it is particularly important to note that this glass must be designed in coordination with the glass manufacturer, as the design is subject to regulations depending on the system provider. The electrochromic panes thus require a special sealed glass pane while the finished gasochromic panes require a triple glazing with 2 gaps between the panes. (compare Figure 0-17) For both versions a wide variety of combinations are possible, which are able to meet a wide range of requirements. Thus, in addition to the obvious use in vertical facades, overhead glazing and glazing systems that can be walked over are also possible. The calculations and designs for the glass strengths are subject to the usual regulations and laws.


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electrochromic Electrochromic compound laminate

GasochromicPane glazing unit gaschromic

Figure 0-17:EC – and GC-functional units After the division of the facade, in which the facade system and glass construction were selected specific to the project, it must now be determined, as with comparable conventional solar shading, which individual panes are switched together into a group. The site use and planned utilisation units associated with this are taken into consideration when forming such groups. The following provides a summary of the important aspects for the formation of groups:

-

The panes within a group all do the same thing. That is, the degree of colouring of the panes within a group is the same for all these panes.

-

The smallest possible group for both systems is the individual pane. Groups as large as desired can be formed by joining together individual groups via the electronic control.

-

Large individual groups are more economical, as the system components, only necessary once per group, can thus be used optimally.

-

Groups can be joined together both horizontally and vertically depending on requirements.

Equally different from conventional insulation glazing, it is important for the manufacturer of switchable glazing to know which position the pane will have with respect to the connections. A detailed position plan for the glazing should therefore be drawn up at the time of the order. This plan should contain the view of the facade including the groups formed and the position of the panes. In addition to this view, a ground plan in schematic form at least, must clearly show the installation system of the individual panes. This plan will form the complete work basis for the building site if the electrical or piping process is entered in it. The following diagram is an example of such a plan:


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M usterfassade Sample facade

1.1

3.1

3.1

1.2

2.1

2.2

1.3

3.2

2.3

1.4

3.3

2.4

Sü

d

gas inlet Gaseinlass gas outlet Gasauslass Figure 0-18:Position and connection plan for facade example

6 Mounting instructions A delicate material like glass also requires sensitive handling. This is particularly the case when a high-quality product like switchable glazing is handled in the rough conditions of a building site. Here careful handling during production is of no avail if equal care is not taken during mounting on the building site. As a result, the manufacturers of these systems, as with all system providers of high-quality products, also stipulate an initial training. For the permanent operating safety of these systems it is necessary for these to be installed and, above all, put into operation by trained personnel only. The following will outline the most important general regulations for handling insulating glazing as well as the most important special regulations for working with switchable glazing.


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6.1

Page 96 of 99

General glazing guidelines Insulating glass panes must be transported and stored upright and on suitable transport frames using glass suction pads. Storage or transport in a horizontal position is not permitted.

The insulating glass must be protected from contact with sharp or pointed objects and must not be rested directly on an edge or corner.

The insulating glass must be stored either in a dry, well-ventilated room protected from the effects of weather, or in the open using covers. The covers are necessary to protect the pane edge seal from damage by UV radiation and to prevent heat cracks caused by heat build-up between the stored panes.

The insulated glass units must be fitted in such a way that the pane does not assume any supporting function, rests tension-free in the structure and cannot be burdened statically or dynamically by the structure under unfavourable conditions.

After fitting the glass, this must not come into direct contact at any point with the structure. The glass pane must only have contact with the seals or sealants.

When in a fitted state, the panes are stored using supporting and spacer blocks. The following figures show the arrangement of these blocks for the most important fitting types:

fixed glazing

vent wing

bottom hung

tilt and turn window

Supporting block spacer block

6.2

Special instructions for working with switchable glazing As already mentioned in the previous chapter, switchable glazing has a connection for pipes or electrical cables in contrast to conventional glazing. This connection leads directly to the pane edge seal. As a result of this:

Stress on the pane caused by tension or pressure from the connection can cause damage to the pane edge seal with the result that the tightness and hence functioning of the insulating glass pane is no longer guaranteed.


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Pane connections rendered unusable through tearing-off or deformation can only be repaired in the factory of manufacture at great effort and expense and only to a certain degree of damage.

During storage, transport, fitting and when fitted it must be ensured that the pane connections are free from any type of strain for the reasons given above.

All panes undergo the strictest quality controls in the factory of origin and are supplied in the coloured state. A pane damaged during transportation can thus easily be identified as such if it is partially or fully bleached.

Before installing the panes it must be checked whether the individual insulating panes are uniformly coloured. In the event of a bleached pane it must be assumed that it has either been damaged during transportation or storage or when being handled on the building site. Attention: Different panes which vary in the degree of colouring do not indicate a defect, as the degree of colouring of the different panes should not be compared until the system is brought into operation!

7 Documentation of a project As with every technical product it is also important for switchable glazing to provide documentation for the glass used with its exact production number and where possible type plate. The position and status of the electrical cables, pipes and other components should also be documented for checking purposes. This documentation also contains the information on group forms already gathered in the planning phase, supplemented by potential changes made during the construction period and above all the assignment of the production numbers to the pane positions shown in the position plan. The adjacent drawing shows such a documentation plan.


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8 Literature /1/

prEN ISO 10077-2 Thermal performance of windows, doors and shutters – Part 2 Numerical method for frames, CEN/TC89 N 793E (February 2001)

/2/

prEN 14351 Windows and external pedestrian doors. Product standard CEN/TC33 (2001)


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Technical Guidelines

Technical Guidelines

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