Integration of technology components in open cladding systems
Integration of technology components in cladding systems Philipp Molter1, Tina Wolf2, Michael Reifer3, Thomas Auer4 1 Philipp Lionel Molter, Technische Universitaet Muenchen, Department of Architecture, Associate Professorship of Architectural Design and Building Envelope, Arcisstraße 21, 80333 München, Tel: + 49 89 289 28462,
[email protected] 2 Tina Wolf, Technische Universitaet Muenchen, Department of Architecture, Associate Professorship of Architectural Design and Building Envelope, Arcisstraße 21, 80333 München, Tel: + 49 89 289 28699,
[email protected] 3 Michael Reifer, Frener und Reifer, Via Alfred Ammon Straße 31, 39042 Bressanone, Tel. +39 0472 270158,
[email protected] 4 Thomas Auer, Technische Universität München, Chair of Building Technology and Climate Responsive Design, Arcisstraße 21, 80333 München, T: +49 89 289-23815, F: +49 89 289-2385,
[email protected]
This paper presents an evaluation of unitized façade systems integrating energy harvesting devices and their synergetic potential to improve internal thermal as well as visual comfort. Todays cladding systems for contemporary office buildings are divided in two different design approaches: For the premium market segment, mostly bespoke solutions are designed to meet the architects design intent. But for more than 90 per cent of Europe’s building market, performance needs to match a certain price range (Construction Perspectives and Oxford Economics 2011). In the last years, several ready designed ‘façade products’ have been offered by façade companies integrating energy harvesting components, natural as well as decentralized mechanical ventilation components and sun shading devices. The integration of energy harvesting devices as well as technical devices to improve internal comfort conditions have a major impact on thermal and visual performances of a façade design. Most devices to improve internal comfort are opaque and reduce solar gains but also the level of natural light in the internal spaces. This opacity also obstructs direct views of users. Some devices are translucent and can act as sun shading device or even regulate daylight by redirecting direct radiation towards internal spaces. Key aspect of this work is the dichotomy of diverse requirements of a modern building envelope in a tangible integration of technical components in a unitized cladding system. This paper focuses on an exemplary integration of an energy harvesting element using solar thermal components in a fully glazed office façade investigating to what extent active solar façade components can be synergistic to provide visual and thermal user comfort. Interior illumination levels and the potential of the energy harvesting façade as a sun shading device are evaluated in an in situ test cell at the Technical University of Munich and are majorly taken from a PhD thesis “Integration of technology in open cladding systems: Design and development of a multifunctional façade module focusing on the evaluation of a case study in a holistic context.” façade, technology integration, energy harvesting, design strategy for office facades, daylight in office buildings, solar thermal facades enegy harvesting building envelope,
Integration of technology components in open cladding systems
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Introduction
Today’s office buildings are aiming for ambitious reduction of energy consumption. However, a comparison of the typically consumption of primary energy ratings for office buildings shows the impact of this building typology in regards to its use of energy. The following numbers reveal electricity consumption for building services systems as well as lighting and energy for heating (Pfafferott, J., & Kalz, D. 2007): - air-conditioned buildings (existing building): 654 kWh/m2 - average office building (air-conditioned and non air-conditioned, existing building): 424 kWh/m2 - new office buildings and (standard segment): 200 kWh/m2 - optimized office buildings 100 kWh/m2 The predominant cause for the above mentioned energy consumption is the provision of comfort of interior spaces. However, the building envelope serves as an interface between the inside and outside and filters or absorbs physical Energy flows towards the interior of a building. The ‘comfort’ depends on personal perceptions and also on temporarily changing feelings of an individual user. It mainly consists of four comfort parameters:
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visual comfort thermal comfort acoustic comfort supply of fresh air
Those four comfort parameters are essential for human well-being and human performance. The regulation of those parameters define also the Energy performance of a building. Visual comfort: The visual comfort defines the conditions of the human environment in terms of lighting levels, glare, light distribution and light color. For the users the main aspects of visual comfort are:
- the comfort of human beings that provides the feeling of well-being - the performance which enables working people to manage visual tasks even under difficult circumstances over a long time period. However, adequate supply of daylight is a very important component for human health and therefore the building envelope needs to provide precise regulation of glare, illuminance, brightness, luminous flux. This can basically be achieved by a kinetic change of a translucent or opaque material, blocking or redirecting daylight into the building. In building envelopes, this means glare control textiles, light shelves, (venetian) blinds. (Cremers, J. 2015) Thermal comfort: Thermal comfort is very much related to the air temperature as well surface temperature of our human body. It is further depending on physical activity, age, gender, surface temperatures, humidity, air speed and insulation between human body and surrounding space. Most of these parameters are significantly driven by the performance of the building envelope by Sun shading devices, thermal insulation materials, radiation reflecting or absorbing materials. (ASHRAE Standard 1981) Acoustic comfort: just as the regulation of the above mentioned parameters, acoustic comfort ensures performance and well-being of our internal spaces. “Acoustic comfort” is achieved when the workplace provides appropriate acoustical support for interaction, confidentiality, and concentrative work by regulating noise levels, sound absorption, sound attenuation, sound insulation and reverberation time. The building envelope provides mostly high sound insulation from exterior to the interior of a building by using sound absorbing surface towards interior spaces. Fresh air supply: besides human emissions of CO2 and humidity, gases, odours, biological impurities that transmit diseases, aerosols and dust require sufficient amount of approximately one volume exchange per hour of an internal space. This is one of the most important Energy consuming parts of a building. And since recent buildings tend to become more and more airtight, an autonomous decentralized ventilation system providing fresh air supply is the focus of various researchers working on adaptive building envelopes. However, the regulation of the above mentioned comfort parameters has been managed in centralized systems over the last decades. Therefore, office buildings have been equipped with huge Heating, Ventilation and Air Conditioning (HVAC) systems consuming significant amount of electrical power in order to ensure static comfort to changing exterior climate conditions. 50% of energy consumption in buildings is caused by HVAC systems which represents one fifth of the total national energy use of European countries. And a massive growth in energy consumption in the EU, is predicted. (Lombarda, L. Ortiz, J. Pout, C. 2008)
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Integration of technology components in open cladding systems
But besides energy consumption the demand of additional space in cores, suspended ceilings, basements and rooftops, this conventional building system requires significant space for ducts and machinery within the building volume. Thus, modern building envelopes tent to regulate the four comfort parameters within the façade units by integrating decentralized devices in order to avoid additional space and installation. In the last years, several ready designed ‘façade products’ have been offered by façade companies integrating energy harvesting components, natural as well as decentralized mechanical ventilation components and sun shading devices within unitized façade systems. The systems Schueco E2, Wicona TEmotion, as well as the mppf developed by the University of Graz, show the state of the art. The main design strategy of the integration of technical devices for internal comfort and energy harvesting into façade products is a modular unitized system. To respond to the dynamic needs of the outside climatic conditions, those façade products address changing weather conditions by regulating façade properties using adaptable devices. Its individual components (modules) are interchangeable and can react differently and specifically to the dynamics of specific contexts. The diverse requirements on indoor comfort as mentioned above require defined layers within the facade regulating changing external climate conditions. Those layers can interfere as well have synergetic effects with energy harvesting elements integrated in the building envelope. This paper focuses on an exemplary integration of an energy harvesting element using solar thermal components in a fully glazed office façade investigating to what extent active solar façade components can be synergistic to provide visual and thermal user comfort. The façade panel was created as part of the BMU-funded project "Development of solar thermal façade panels with vacuum tubes in office buildings (FKZ 0325956A)". It consists of two connected parts: fully glazed façade panel featuring a triple glazing unit (0,5 W/(m²K) for the unit) of the Wicona Wictec series. A second layer is composed of a layer showing vacuum tubes and e perforated mirror aligned to the sun, which on the one hand effectively draws the radiation onto the absorber layer of the tube, and on the other ensures transparency in the façade. In addition to this selective transparency and the optimized utilization of solar radiation, it provides a sun protection function, which prevents glazed office buildings from overheating.
Fig. 2 (left) and Fig. 3 (right) : façade module integrating solar thermal energy harvesting unit.
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Integration of technology components in open cladding systems
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Methodology
The above mentioned façade unit is tested in regards to its thermal and visual comfort performance. Therefore, interior illumination levels and the potential of the energy harvesting façade as a sun shading device are evaluated in an in situ test cell at the Technical University of Munich. This in situ test cell installed on the roof of the main TU building at a height of about 28 m above ground allows the assessment of the thermal performance of facade elements in one to one scale under natural climate conditions. The cell is south oriented with a 23° rotation towards west. All relevant temperatures as surface temperatures of the adjacent walls ceilings and facades as well as heat fluxes and the weather data are recorded continuously. The cubicle features high insulated exterior walls (U-Value 0,24 W/m2K)
Fig. 4 (left) test cell and sun path diagram left part fully glazed unit right part semi-transparent collector wall. Fig. 5 (right) in situ test unit at the TU München.
The testing series are divided in two series of measurements:
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thermal measurements are set up as comparative measurements to conventional façade systems. They allow architects a concrete and descriptive evaluation that can be compared to a habitual reference. Thus, in addition to an absolute measured value an understanding for non experts can be ensured. The so called “sun shading potential” represents the portion of radiant energy (heat) of a building that can be reduced by an external sun protection. measurements in regards to the visual comfort focus on glare, light distribution, external visual reference, Daylight Factor, level of illuminance.
The experiment
In order to evaluate the proposed design, a series of measurements aiming on the above mentioned thermal and visual comfort were undertaken. The focuses of the research question are: To what extent can active solar façade components be synergistic to provide visual and thermal user comfort? Can the overlaying functions of a semi transparent façade integrated solar thermal collector serve as a sun shading device and ensure at the same time a sufficient level of daylight besides acting as a energy harvesting exterior envelope? In a fist stage, the test cell was divided in two similar test cells, both of them had opaque high insulated walls (UValue 0,24 W/m2K). The south facing wall of each test cell was clad with a test subject as shown in fig.4/5. Between 10.00h and 14.00h, the respective angles of the solar radiation are 10.00h: 57.3 °, 12.00h: 60.5 °, 14.00h: 47.4 °. In the case of a cloudless sky, the temperature in measuring room A (without shading device, without collector field) rose by 7.90K from 24.30 ° C to 32.23 ° C. Compared to this, a temperature increase of 5.2K from 22.80 ° C. to 28.05 ° C. resulted in a temperature rise of 4 hours around the solar level. From 12.00h the global radiation decreased continuously and reduced to 100 W / m² in a slightly cloudy sky. Nevertheless, the temperature range rose from 14.00h (47,4°) to 16.00h (28,4°) in room A from 32.23 ° C to 38.82 ° C,
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Integration of technology components in open cladding systems
while the room air in room B of 28, 05 ° C to 31.46 ° C by 3.46K. (The values in brackets describe the angle of solar irradiation) In the following two hours, global radiation fell significantly (to 522 W / m²). Thus, the temperature of the measuring chamber A also fell, since it was at a high temperature level at 38.82 ° C. at 16.00 h. The temperature of the measuring chamber B rose slightly further from 31.46 ° C to 31.54 ° C. This is due to the absorbed heat of the floor, which is now dissipated, since the air temperature was significantly lower than that of the test room A. The temperature difference relative to the volume of the room generated by different solar entries of the south-facing façades reached a maximum of 7.34 K. On a completely cloudless day, the temperature difference could certainly have turned out to be even more pronounced, since very high differences were observed in direct sunlight. The measured difference of 7.34 K at 16.00h between 38.82 ° C in test room A and 31.46 ° C in test room B is considered as a reference point of a sun protection potential against an unshaded façade and is related to the test room, the angle of solar radiation and The climatic conditions of the day.
Fig. 6 thermal behavior of two test cells on a summer day. (21.07.2010)
In a second stage, several measurements were undertaken. Therefore, a comparative assessment process had been set up in an in situ test cell unit. The unit was divided in two similar test cells, both of them had opaque high insulated walls. The south facing wall of each test cell was clad with a test subject as shown in fig.4/5. One part was equipped with a functional module integrating solar thermal collector unit, the other part was equipped with a base module without functional module. Both cells were compared in regards to their temperature behavior of the inner space of the test cells at a summer day. The solar radiation would heat up both cells. The unshaded test cell shows a higher temperature level than the test cell which was clad with the semi transparent collector unit. Thus, the test cell showing the lower temperature level was heat up using a heat fan. The supplied electricity to align both temperature levels of both test cells represents the above mentioned “sun shading potential” of the semi transparent solar thermal façade collector. It is depending on the sun angles azimuth and altitude, global and direct radiation, exterior temperature as well as eventual clouds and meteorological interferences in order to be comparable to other in situ measurements. Several series of measurements of the different components were investigated, exemplarily, this paper focuses on the following results.
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Integration of technology components in open cladding systems
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Results
At a summer day (July, 22nd 2010) with high level of radiation, the following sun shading potential was calculated: 638,96 W for the test cell, which represents a relative sun shading potential of 156,03 W/m2 (test cycle 2h, sun angles: 41,32°-21,49°, 815 W/m2 Global radiation)
Fig. 6: Temperaturebehaviour of the test cells: Curves of both test units on a summer day. (22.07.2010)
The second measurements undertaken were in regards to the visual comfort. The façade unit integrating the solar thermal collector unit was evaluated in regards to the following aspects. The opaque parts of the façade collector create shaded parts in the adjacent internal spaces. Behind the semitransparent solar thermal collector façade module a desk was installed. (fig. 7) On the desktop surface the lighting levels were measured. The investigations of the façade on the interior focused mainly on differences in luminance differences between shaded and non shaded parts of the desktop. The measurements were undertaken on days with high global and direct radiation proportions. On a cloudless day, direct sunlight penetrated directly through the semitransparent collector. The sensors were alternately exposed to direct sun light. Simultaneously other parts of the desktop were shaded by the opaque absorber surfaces of the tubes. The measured intensities of illumination levels showed more than 16,000 lux in the parts receiving direct solar radiation, while at the same time the shaded parts received less than 500 lux. The solar thermal collector provided partly shadow for the internal spaces behind. However, the opaque parts of the absorbers alter with transparent parts, which creates differences in levels of luminance, which causes glare to human eyes. In the direct field of view a ratio of 5,543 : 1 was measured, due to a pattern that occurred on a working desk surface by the differences between shaded and non shaded parts behind the semi transparent wall. For the extended field of view, a ratio of 11,666 : 1 was measured due to an extraction of light/radiation from the solar tubes which were exposed to direct sun light. According to DIN, a the ratio of levels of luminance which lead to glare, must not exceed 3:1 for the direct field of view and 10:1 for the extended field of view. For the same façade module (Semi transparent façade unit integrating a solar thermal collectors) a daylight factor of 1,25had been measured.)
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Integration of technology components in open cladding systems
Fig. 7: measurements to the visual comfort: levels of illuminance
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Conclusion
Especially in situations with lower sun angles, in the morning and the evening hours during the summer months, significant amount of solar gains were measured. In these cases, the increase of temperature behind the facade collector is very high. The static sun protection effect is evaluated with an Fc value of 0.45 on the basis of the measurements. This means that an additional sun protection is necessary. The investigations on visual comfort show the complexity of the dialectic between energy production and the daylight properties of a façade: the energy-winning elements impair the transparency and thus the continuation of the light supply into the interior. Moreover, the energy harvesting façade components and can not adapt to the changing external daylight intensities. The measured lighting levels above 16,000 lux require additional glare protection.
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Integration of technology components in open cladding systems
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