Daylighting and occupant health in buildings

Daylighting and occupant health in buildings

Douglas Cawthorne Peterhouse

Dissertation submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy University of Cambridge Department of Architecture September 1995

Declaration This dissertation is my own work and contains nothing which is the outcome of work done in collaboration. The work of others is correctly cited. This dissertation is less than 80,000 words in length, including footnotes, appenidices, references and bibliography. None of the dissertation has been previously published in this form, nor submitted for any other qualification or degree.

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Summary Daylighting and occupant health in buildings Douglas Cawthorne Peterhouse The objective of this thesis has been to identify a particular range of effects that the daylighting design of buildings has upon the health and comfort of building occupants and in particular upon daylight induced modulation of the human circadian cycle. This aspect of daylighting is studied in detail within the broader context of its potential impact upon the current trend towards optimising energy efficiency in buildings. Optimising aspects of building performance such as energy efficiency has had a profound influence upon the human experience of buildings. These have not always been positive and for one particular class of negative experience a causal mechanism is proposed in which circadian dysfunction plays a significant role and which suggests a link between the previously unrelated clinical phenomena of Seasonal Affective Disorder (SAD) and Sick Building Syndrome (SBS). A brief resume of current issues involved in addressing the problems of energy efficiency and occupant comfort and health in buildings is provided along with an overview of daylighting and occupant health in buildings in both a historical and a contemporary context. The main body of the work describes the two vehicles which have been used for exploration and support of a building mediated circadian dysfunction hypothesis. The first is a series of field measurements of the light exposure of building occupants in different generic building types. The second is a series of integrated parametric analyses using a new computer model which simulates the effect of building design and location within the urban fabric upon the circadian cycle of occupants. Both field studies and computer simulations are used to suggest beneficial modifications to current design strategies in buildings that may help to minimise occupant dissatisfaction with the internal environment and maximise some aspects of occupant health and well being. Results from the original work carried out for this thesis indicate that both the physical design of buildings and the occupant behaviour pattern in building use has a non-trivial effect upon the health and well-being of occupants and consequently upon the occupant acceptability of some performance led energy efficiency and daylighting design measures. As a result of these studies it has become clear that certain generic types of building and certain types of building layout within urban fabrics are more amenable to integrated energy and occupant health optimisation than others.

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Acknowledgements I am grateful to the many people who during the course of this work have contributed ideas, comments and encouragement. In particular I would like to express my thanks to Dr. Nick Baker of the Martin Centre who as my PhD supervisor has unstintingly given of his time and experience in directing this research. Of the past and present staff and students at the Martin Centre, all of whom have made it such a pleasant place in which to work, I would particularly like to thank Guy Newsham, Tim Lewers and Tony Shadbolt for the three years of quiet humour we enjoyed in our little office and for their constructive comments on the mathematics and programming of the GOLD model. Thanks also to Koen Steamers for his comments on urban design and energy issues and to David Crow1her for sharing his encyclopaedic knowledge of building related health issues. Of those colleagues elsewhere I would particularly like to thank Dr. Robert Headland of the Scott Polar Research Institute in Cambridge for his help in tracing the often obscure references to Seasonal Affective Disorder (SAD) in the polar literature and Dr. Anna Wirz-Justice of the Psychiatric Institute in Basel, Switzerland for advising on the validity of circadian rhythmicity models. I would also like to express my thanks to Professor Dean Hawkes for his valuable comments on the theory of models in the design process, and to Dr. Mike Wilson for his advice on daylighting and indoor illuminance. To all the staff at Cambridge Architectural Research Limited I owe a considerable debt of gratitude for the innumerable occasions on which they put work aside to give practical help and advice when it was most needed. Finally my most sincere thanks go to my parents, Jen and Clifford Caw1horne who have given constant material and moral support throughout my work on this research. This work was funded by a Science and Engineering Research Council studentship between October 1988 and September 1991 . Additional funds for travel were made available in 1989 by Peterhouse.

iii

The SI lighting units The following SI lighting units and definitions are used throughout this work and are taken from Joseph B. Murdoch, Illumination Engineering, MacM illan, 1985, pp. 22-25:

Symb ol

Con ce pt

Metric Unit

Imperial Unit

I

Luminous intensity or candlepower

Candela (cd)

Candela (cd)

Luminous flux•

Lumen (Im)

Lumen (Im)

E

llluminance

Lumen per square meter {lux (Ix)}

Lumen per square foot {footcandle (fc)}

M

Luminous exitance

Lumen per square meter (Im I m2)

Lumen per square foot (Im I tt2)

L

Luminance

Candela per square meter (cd / m2)

Candela per square foot (cd I tt2)

Q

Quantity of light

Lumen-second (Im . s)

Lumen-second (Im. s)

* Luminous flux corresponds to power in the radiation system and quantity of light corresponds to energy. Thus the lumen and the watt are the same dimensionally, as are the lumen-second and the joule (watt-second). The basic unit from which all others are derived is the candela (cd) which is the unit of luminous intensity (I) in a specified direction. The magnitude of the candela was defined in 1948 as such that the luminance of a blackbody radiator at the temperature of solidification of platinum is 60 candelas per square centimetre. This definition was refined in 1979 to standard radiometric quantities thus: "The candela is the luminous intensity in a given direction of a source which is emitting monochromatic radiation of a frequency 540 x 1012 Hz (555nm) and whose radiant

1

intensity in that direction is W/sr." The unit of luminous flux () is the lumen (Im) and is the 683 rate at which luminous energy is incident on a 1m2 surface 1m away from a uniform point source of 1 cd intensity. A uniform 1 cd point source emits 47t Im. Luminous flux is the time rate of flow of luminous energy. This makes the lumen dimensionally equivalent to the watt, which is the time rate flow of energy. The two can be related through the spectral luminous efficiency curve of the human eye. The illuminance ( E) falling on a surface is the intensity of luminous flux incident on that surface . Thus where A is surface area:

E= A The unit of illuminance is the lux (Ix) in the SI system, being a lumen per square meter. The inside of a sphere receives 47t Im from a 1 cd point source. Since the sphere's surface area is 47t m2, the illuminance on the inside surface of the sphere is 1 Ix. In order to know the density of luminous flux leaving a surface two concepts are required, one to describe the total luminous flux density leaving the surface and the second to describe the luminous flux density leaving the surface in a particular direction. The former concept is provided by luminous exitence (M), the latter by luminance (L}, defined as the density of luminous intensity in the direction of viewing. Quantity of light ( Q) is luminous energy and is related to lu minous flux, which is luminous power, through the parameter of time. The lumen is used as the measure of luminous flux and the lumen-second or lumen-hour is used as the measure of light. The lumen-hour may be used in the same way as the kilowatt-hou r, in evaluating the consumption of energy, in this case luminous energy over extended periods of time.

iv

Contents Chapter

Pag e

Summary Acknowledgements

iii

The SI lighting units

iv

Contents

v

1.

1

Buildings, lighting and the biological clock

1 . 1 Occupant comfort and health as performance criteria in building design 1. 1. 1 Summary 1.1 .2 Buildings as climate modifiers 1.1 .3 Energy efficiency in building design 1.1 .4 Integrated design tools 1.2 The role of daylighting in occupant health 1.2.1 Summary 1.2.2 Daylighting and general health 1.2.3 Daylighting and the circadian timing system 1.2.4 A model of the circadian timing system 1.2.5 Seasonal Affective Disorder (SAD) 1.3 The photo periodic effect hypothesis 1.3.1 Summary 1.3.2 Daylighting and Sick Building Syndrome (SBS) 1.3.3 Hypothesis 2.

Investigating light exposure in buildings

2. 1 The photographic light dose meter 2.1 .1. Summary 2.1 .2. Measuring light exposure 2.1.3. Description of the dose meter 2.1.4. Operation of the dose meter 2.1.5. Experimental trials using the dose meter 2.2 The electronic light dose meters 2.2.1. Summary 2.2.2. Description of the electronic light dose meter 2.2.3. Calibration of the electronic light dose meter 2.3 The light exposure case studies 2.3.1. Summary 2.3.2. Purpose and methodology of the studies 2.3.3. Examples of light exposure 2.3.4. Characterising light exposure 2.3.5. Assessing thresholds 2.3.6. Interpretation of results 2.4 Daylight factor surveys 2.4.1. Summary 2.4.2. Predicting retinal illuminance 2.4.3. Measurement of daylight factors 2.5 Assessing occupant behaviour patterns 2.5.1. Summary 2.5.2. Data on occupant behaviour 2.5.3. Building and occupant movement interaction 2.6 Assessment of circadian phase shifting 2.6.1. Summary 2.6.2. Measuring circadian phase 2.6.3. Circadian variations in mental efficiency

1 1 1 2 7 8

a

8 13 15 20 25 25 25 30

42 42 42 42 43 45 47 49 49 49 51 53 53 53 56 59 61 62 66 66 66 68 70 70 70 72 74 74 74 75

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2.6.4. 2.6.5. 2.6.6. 2.6.7. 2.6.8. 3.

The AGARD stress battery Experimental methodology Results of the AGARD stress battery tests Self assessment of comfort and health Results of the SOMNUS alertness tests

Modelling light exposure in buildings 3.1 The theory of models 3.1.1. Summary 3.1.2. Simplification 3.1.3. Efficacy 3.1 .4. Abstraction 3.1.5. Hierarchy 3.1.6. Realism and usefulness Design techniques and values 3.1. 7. 3. 1.8. The purpose of GOLD 3.2 The history of daylighting models 3.2.1. Summary 3.2.2. Definition of a model 3.2.3. Early daylighting models 3.2.4. Greek and Roman models and exemplars 3.2.5. Renaissance daylighting models 3.2.6. Daylighting models and light measurement 3.2.7. Daylighting models and legislation 3.2.8. Contemporary daylight modelling 3.3 The GOLD Model 3.3.1. Summary 3.3.2. GOLD as a research tool 3.3.3. GOLD as a practical design tool 3.3.4. The sky luminance distribution algorithm 3.3.5. The window angle algorithm 3.3.6. The external obstructions algorithm 3.3. 7. The roof lights algorithm 3.3.8. The reflected components algorithm 3.3.9. Sun patches and horizontal illuminance output 3.3.1 O. Code structure of the GOLD daylighting model 3.3.11. The light dose algorithm 3.3.12. Zones of occupancy 3.3.13. The horizontal illuminance distribution routine 3.3.14. The circadian phase shifting algorithm 3.3.15. The user interface

4.

Validation of the G.O.L.D. model 4.1 Validation and verification 4.1.1. Summary 4.1.2. Assessing the validity of the model output 4.1.3. Verification of the solar geometry code 4.1.4. Verification of the Sky luminance model code 4.1.5. Verification of cosine angle of incidence and glass absorbency code 4.1.6. Verification of the window angle code

5. Parametric studies using the G.O.L.D model 5.1 Elemental parametric assessment 5.1 .1. Summary 5.1.2. Assessing the behaviour of the GOLD model 5.1.3. Elemental parametric assessment 5.1.4. Testing primary building variables 5.1.5. Room orientation 5.1.6. Length of room

77 79 80 81 82

85 85 85 85 86 87 88 90 92 93 94 94 94 95 96 104 107 109 110 120 120 120 121 122 126 127 129 130 133 133 135 136 137 138 140

143 143 143 143 147 149 151 152

158 158 158 158 159 165 166 167

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5.1.7. Width of room 5.1.8. Height of room 5.1.9. Ceiling reflection 5.1.10. Floor reflection 5.1.11. Window side number 5.1.12. Window length 5. 1.13. Window to left Wall 5.1.14. Heightofsill 5.1.15. Height of window 5. 1.16. Testing primary urban variables 5.1.17. External obstruction reflectance 5.1.18 . External obstruction height 5.1.19. External obstruction distance 5.1.20. Height and width of the subject building 5.1.21. External overhang width 5.1.22. External overhang height 5.1 .23. Testing primary occupant variables 5.1 .24. Testing primary zone variables 5.1.25. Testing primary temporal data 5.1.26. The relative significance of variables 5.2 Integrated parametric assessment 5.2.1. Summary 5.2.2. Purpose and methodology of integrated parametric testing 5.2.3. Room orientation 5.2.4. Room width 5.2.5. Window length 5.2.6. Sill height 5.2.7. Window height 5.2.8. External obstruction distance 5.2 .9. External overhang width 5.2.10 . The relative significance of key variables 6.

Integrating occupant movement behaviour 6.1 Occupant movement in the workplace 6.1.1. Summary 6.1.2. Representing occupant movement 6.1.3. Timetables 6.1.4. Occupant movement and light dose 6.1.5. Analysis of six zone layouts 6.1.6. Quantitative comparison of circadian phase shifting 6.1. 7. Zone layout 1 6.1.8. Zone layout 2 6.1.9. zone layout 3 6.1 .10. Zone layout 4 6.1.11 . Zone layout 5 6.1.12. Zone layout 6 6.1.13. The finite space dilemma 6.1.14. llluminance outwith the workplace 6.1.15. Control over light exposure

7.

Case Studies

7 .1 Circadian phase shifting in an existing office building 7.1.1. Summary 7.1.2. Developing building designs from research 7.1.3. Circadian phase shifts in an existing office building 7.1.4. The effect of energy efficiency modifications 7 .2 Developing the office for optimised circadian phase shifting 7 .2. 1. llluminance distribution and circadian phase shifting 7.2.2. The BAE average sky model and the effect of glazing orientation.

168 1 68 169 170 171 171 172 173 173 17 4 175 176 177 177 178 179 180 181 181 182 184 184 184 187 190 192 193 194 195 196 197 201

201 201 201 202 205 207 208 210 212 214 215 2 17 219 223 224 229 232

232 232 232 234 238 244 246

249

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8.

Integrated design strategies 8.1 Formulating design guides for circadian good practice 8.1.1. Summary 8.1.2. Courtyard office buildings 8.1 .3. Exclusive design 8.1.4. Selective design 8.1.5. Mixed mode design 8.1.6. Forming an integrated design using key variables 8 .1 .7. Global and regional location 8.2 Building form 8.2.1. Obstructions and the urban morphology 8.2.2. External obstructions as reflectors 8.2.3. Louvered building envelopes 8.2.4. Context and orientation of glazing 8.3 Fa~ade design 8.3.1. Refining the fa~ade design 8.3.2. Sill height 8.3.3. Shading devices 8.3.4. Light shelves 8.3 .5. Potzdammer Platz - a recent example 8.3 .6. Accommodation use and favade design 8.4 Occupant behaviour and control 8.4.1. Daylighting and zoning according to use 8.4.2. Artificial lighting control strategies 8.4.3. Interior furnishings

253 253 253 254 254 255 256 258 260 262

263 266 268 271 273 273 274 274 275 276 279 279 280 282 284

Conclusions

285

References

290

viii

1. Buildings lighting and the biological clock

1. Buildings lighting and the biological clock 1.1

Occupant comfort and health as performance criteria in building design 1.1.1

Summary

A case is made fo r the health and well-being of building occupants to occupy a more significant position than they have to date in the design of buildings.

1.1.2 Buildings as climate modifiers Western Europeans spend approximately 85% of their lives in buildings 1 a fact which invests in buildings a central role in western society and which imparts an extensive socio-economic overlay to them that can often obscure the principal reason for their existence. This is that buildings modify the environment (in its widest sense) so that people can carry out activities that would be uncomfortable, arduous or impossible otherwise. However, it is widely recognised that buildings are first and foremost climate modifiers, which alter climatic parameters like air temperature, humidity, air speed, precipitation and solar radiation amongst others so that human activities can be carried out within acceptable limits of comfort and health 2. It is these components of the indoor climate, amongst others, that are the fundamental building blocks of architecture, rather than is often assumed the bricks and mortar that are used to manipulate them. To the architect whose province is the design of buildings, these simple facts are often sublimated by the complex process of producing buildings. Because architects (like most people) think visually, anything which can be described easily by pictures is most intuitively understood and acted upon in preference to problems that require non-pictorial abstraction. This has focused the attention of architects on the physicality of the fabric of the building rather than upon the end objective of building, the indoor climate. It has also emphasised the importance of the visual appearance of buildings, often at the expense of other important aspects of the design. It has also reinforced by default the largely pictorial way information is transmitted about buildings both by architects and by lay people. Because of this there is a common misconception that buildings are static, immovable and unchanging. This is not the case. Transient heat flow and air movement for instance are constantly changing, as is the ambient lighting environment. The dynamics of other, non-visualizeable parameters operate over

1


much greater time scales, for instance structural settlement or large scale urban growth and decay which may be only significantly perceptible over years or decades. These characteristics of the way people perceive buildings in general may have militated against the climatic aspects of buildings being addressed more meaningfully in the development of building designs. This is now a significant problem. "Climatic" aspects of the physical environment determine to a large extent how we feel and behave, but human comfort and health can only be maintained between comparatively narrow bands of the dynamic range of most climatic parameters. Outwith these bands people become progressively more uncomfortable or ill (see figure 1.1 ).

Vapour pt essuro

( mb I

Figure 1.1 For a given level of activity, clothing and air speed a psychometric chart may be constructed showing the comfort zone outwith which conditions will be unacceptable to normal occupants. In this case the comfort zone is that defined by ASHRAE Standard 55-74 and is the shaded area. From Indoor climate, D.A. Mackintyre, Applied Science publishers 1980.

1.1.3 Energy efficiency in building design Since the energy crises of the mid 1970's there has been continuing pressure on architects and services engineers to make buildings more energy efficient in a variety of ways 3. This has been reflected in the UK building regulations where there has been a continual increase in the insulation required in domestic buildings 4. Year 1965 1976 1982 1990 Table 1.1

Roofs 1.42 0.60 0.35 0.25

Walls 1.7 1.00 0.60 0.45

Floors 1.42* 1.00* 0.60* 0.45**

U-Values required by the building regulations, from BRE digest 355. *applies to exposed floors only ** applies to all floors including those in contact with the ground

Despite energy being cheaper and more freely available now than during the oil embargoes of the 1970's, concerns about C02 and CFC emissions into the

2


atmosphere and the problems associated with global warming have maintained the drive to reduce primary energy consumption in buildings s, 6. Buildings are major consumers of energy for space heating, lighting, refrigeration , ventilation and other services. This energy together with that used for domestic appliances and office equipment amounts to approximately half of the total UK demand for energy and is the source of a similar proportion of all energy related C02 emissions s.

I

Fuel Petroleum Electricity Gas Solid Fuel Totals

Buildings

Industry

325 650 1540

250

Transport 1760

280

25

360

l 2875

530 370 I 1430

0 5

I 1760

Agriculture

7 10 0 5 I 32

Table 1.2 United Kingdom delivered energy consumption (in Peta Joules {1o15}) by sector and delivered fuel type (1987) from BRE information paper IP 2/90.

Of the approximated total of 2875 PJ delivered energy to buildings in 1987, 1870 PJ was delivered to domestic dwellings and of this over 61 % was used for space heating, 21 % was used for water heating, 7% was used for cooking and 9.6% was used for lights and appliances 5. Consequently considerable effort has been made to reduce the delivered energy consumption of buildings and in particular the space heating requirement. Demands for further reductions in the delivered energy consumption of buildings are probable with the introduction of increased taxation on energy (beginning April 1994) in an effort to reduce the rate of global and local environmental damage. There is a widespread and pro-active energy efficiency and environmental design lobby world-wide and particularly in the UK that is exerting considerable influence on the design of generic building types. Whilst improvements to existing practices such as loft and wall cavity insulation, hot water tank insulation, double glazing 7 and air infiltration a are common, more strategically innovative practices are aJso becoming more widely used. Passive stack ventilation 9 , passive ventilation pre heating and mechanical heat recovery in domestic dwellings 10 for instance are gaining wider acceptance within the UK. Greater interest in energy efficiency has also influenced more fundamental aspects of building design often considered by

architects and building design professionals at the early stages of the design process, such as glazing to floor area ratio, the provision of buffer spaces, plan depth and fenestration orientation 11. Running in parallel with the energy efficiency issues has been a growing concern about the effect of energy efficiency measures in building designs upon the health and well-being of building occupants. A

3


particular example has been the reduction of fresh air ventilation rates in buildings to reduce the space heating and air conditioning load. Ventilation air that passes through a building becomes laden with pollutants, carbon dioxide and odours from occupants, cooking smells, chemicals from appliances and machinery, furnishings and building materials. If the ventilation air is re-circulated or the rate of dilution with pre-warmed fresh air is insufficient then the concentration of pollutants will rise. It is this concentration of pollutants in the indoor air that has been cited as the

cause of a significant degradation of occupant health and wellsbeing in some buildings, a condition known as Sick Building Syndrome (S.B.S.) 12. This syndrome will be explored in more detail later in this thesis. A further example is found in daylighting and artificial lighting in buildings. Where deep plans are favoured for cost effective site coverage, particularly for large city office buildings, artificial lighting is commonly used to achieve acceptable levels of horizontal illuminance of the working plane. This is often implemented using fluorescent luminaires which in themselves consume energy but also if improperly installed or maintained can cause eye strain 13 and headaches 14. It is trade-offs like these between energy efficient design measures and the health and wellbeing of building occupants that have remained largely separate fields of research but are in reality intimately connected. This differentiated approach to consideration of building design is proving to be inadequate in advancing its quality and efficiency across the broad front that is now being demanded by owners and occupiers. This phenomenon of unequal advancement of a broad range of design concerns is not unique to building design. It has been encountered in the aircraft and automotive industries 15. Here however the need to balance increased energy efficiency and material performance against requirements of passenger comfort and safety has been addressed by using highly refined methods of quantitative analysis. Often the lives of passengers and the financial viability of large organisations depend upon the accuracy of this balance between acceptable levels of safety, comfort and efficiency. By comparison it has been argued that increase in building energy performance has not been attended by a commensurate maintenance of acceptable levels of occupant health and comfort. It is posited that inadequate ability to accurately represent the complex interaction of occupant comfort and health, indoor climate and building design has reduced the margins of what might be called "indoor environmental safety" beyond acceptable limits. This is possibly because design

4


professionals and architects in particular lack the refined design tools common in other areas of human endeavour (fike the aerospace and automotive industries) to make informed quantitative to qualitative comparisons. Architects have traditionally relied upon precedents and exemplars and "rules of thumb" 16 in the comparison of the quantitative with the qualitative aspects of building designs. This was adequate in the past because the performance demands being made on building designs were slight in comparison with the resources of materials, time

and energy available to fulfil them. More recently those available resources have been reduced and are continuing to be so. In the absence of more refined design tools, architects attempt to address increased performance demands with the available, traditional "rules of thumb" design tools which inevitably make for wide swings in the success rate of new building designs (as measured by both occupant comfort and health and energy efficiency). Several studies have shown that this is the case 17, 1s and that achieving energy efficiency by both active and passive means while at the same time ensuring that the indoor climatic conditions fall within acceptable boundaries of human tolerance is difficult. Studies carried out on passive solar buildings by the Environmental Monitoring Company in 1987 at Nettley Abbey County infant schoo11s concluded that summer overheating was a significant problem and that 79% of staff wanted more cont rol over the indoor climate. Similar findings have been reported for occupant perception of daylighting and view in deep plan mechanically serviced buildings. These findings are typical of much research into occupant dissatisfaction with passive building design and are responsible for some resistance to the passive concept from those who have traditionally relied upon active mechanical systems. It seems that to date, continuous comfort can not be guaranteed in many contemporary passive buildings in the way that it can be in conventional buildings which have a large amount of mechanical services. In an attempt to understand this contradiction it is proposed that within the concept of both passive and active building design strategies geared to optimise both energy efficiency and occupant comfort and health there lies a fundamental dilemma that is also central to issues of daylighting. It is the problem of dual control.* Minimising primary energy consumption within large and small buildings has traditionally relied upon central (often automated) control of the energy systems, • Dual control is a concept proposed by the author to account for the unpredictability and complex behavioral characteristics exhibited by a certain class of operational systems within buildings.

5


from the computer controlled C.H.P. plant of a large office building to the off-peak storage heater or thermostat in a small flat. Central control can be very effective in doing this but within quite wide occupant comfort bounds. The thermostat may accurately measure the dry bulb air temperature 1.5 meters from the floor but there is often a 1 - 3 degree centigrade temperature gradient between floor and ceiling due to temperature stratification. An occupant sitting down, or near a draughty door, or next to a closed window may not be comfortable despite the

centralised system working well. The result is occupant dissatisfaction or the occupant turning the thermostat up, thereby increasing the energy consumption. Similarly, maximising the comfort of the individual occupant may be effected by giving him or her complete control over their personal bio-climate but the situation is complicated by the fact that each individual's action has an effect on both the personal bio-climate of other occupants and upon the overall energy efficiency of the building. An occupant may be too hot and opens a window for example. The increased airflow removes the unwanted energy from the occupant but the increased air-intake in another part of the building where another occupant is at the right temperature makes that occupant cold. The increased air flow removes energy from the building, the building senses this, more primary energy is required to heat the building and the total energy efficiency of the building drops. In terms of both passive solar buildings and conventional buildings this is significant. If occupants are to be given maximum control over their personal bioclimate (as much research suggests) and yet if th e building is to achieve maximum energy efficiency (as economy and environmental responsibility suggests) then effective control of the building envelope to achieve both end goals would appear to be problematic. Individual occupants will compete with each other by using the building to modify the bio-climate to maximise their own comfort. Automated control systems will compete with all the occupants by using the building to modify the bio-climate to maximise the building's energy efficiency. As observations of population dynamics in nature have revealed where species compete for food, mates and habitat, in a building with such dual control one would expect to see highly complex, non-predictable oscillations in occupant comfort and energy efficiency across all building designs, both conventional and passive. It is suggested that this is in fact what can be observed in the occurrence of non attributable syndromes such as SBS and also in the equally non-specific and non-attributable occupant dissatisfaction with "high performance" passive solar buildings that has been noted in the literature. In many cases, perhaps even

6


the majority the effects may be sub-syndromal but nonetheless significant (see section 1.2).

1.1.4 Integrated design tools A wide range of quantitative strategic and tactical analysis tools 19, 20 have been developed to try to help architects meet the increased energy performance demands being placed on new building designs and to make the interaction of buildings and occupants more predictable. Unfortunately they have not met with the same degree of success that the application of quantitative analysis methods has in many other areas of human endeavour such as the sciences, engineering and medicine. This may be because these tools, although sophisticated in their representation of the climate and the building have adopted without modification the somewhat limited representations of occupant comfort and health that have been used for a number of years. The need to integrate issues of energy efficiency with occupant comfort and health requires that more accurate and wide ranging definitions of occupants be developed. It is the purpose of this thesis to assist in broadening the definition of occupant comfort and health to include a potentially significant and little considered aspect of human health and well-being, daylight modulated circadian rhythmicity. By doing so it is intended to explore the potential for integrating daylighting mediated occupant health issues with energy efficient building design. Limitations of time and resources have necessitated restricting the scope of this endeavour to a pilot study. Many areas could usefully have been investigated in greater detail but the intent has been to map methodologies and a pathway for future research, rather than provide a completely watertight fait accompli. As such, effort has been concentrated on describing the development of experimental, measurement and modelling techniques and the results of their use rather than extensive development of detailed building designs. The development of such detailed design may be carried out in future using the techniques and particularly the computer model described in this thesis.

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1.2 The role of daylighting in occupant health 1.2.1

Summary

There are few areas of our physical or mental functioning that are not influenced by the daylighting environment. Human beings evolved to receive and use daylight in a wide range of ways. Daylight falling on the eyes and skin exercises a subtle control over human well-being throughout our lives and fulfils a number of important roles in maintaining human physical and mental health. Apart from being our primary mode of sensory perception, it is a producer of Vitamin D in the skin, a germicide and a hormonal regulator. Recent advances in clinical research have identified a number of significant hormonal mechanisms mediated by human exposure to daylight. One of the most important of these has been the quantification of the human circadian timing system or "biological clock". The identification of the circadian timing system has allowed confirmation of a long hypothesised correlation between a widespread class of previously unattributable depressive disorders and human exposure to daylight. Of significance to building design professionals is evidence to suggest that the exposure to daylighting that occupants experience in many new buildings are similar to the daylighting regimes which can cause the onset of these depressive disorders in susceptible individuals.

1.2.2

Daylighting and general health

The effect of daylight on human health and well-being is wide ranging. For the purposes of this discussion they can be divided into two groups of effects, those that are skin mediated and those that are eye mediated. In built up urban areas daylight levels within buildings may be lower than they would be in open countryside. Because daylight may not be so readily available in urban areas it has meant that the quantity of vitamin D produced by daylight on the skin is lower than it has been in the past and particularly so in the winter 1. One of the well known results of this in the past in children (coupled with a poor diet) was rickets 2.

Children with rickets develop deformity of the long bones due to lack of calcium,

their teeth fall out and there is a significant weakening of the muscles. At the turn of the century it was estimated that 90% of children in European and north American cities had rickets 2. In 1889 an investigative committee of the British Medical Association clearly stated that there was a relationship between urban industrialised environments and the disease 3. It was shown that vitamin D included in food or created in the skin by exposure to daylight prevented the disease 4.

8


The active form of vitamin D is in fact a hormone produced by the liver and the kidney from the 'raw' vitamin. The sole source of vitamin D production in the body is the effect of ultra violet radiation from daylight on the skin. The primary function of vitamin D is to help the body make efficient use of calcium and it does this in three ways. By increasing absorption of calcium from the digestive system, by reducing the amount of calcium and magnesium lost in the kidneys and passed out in urine, and by increasing the turnover of calcium in bones and teeth,

ensuring that they are strong and healthy. Excess calcium in the blood stream caused by lack of Vitamin D causes hardening of the arteries and an abnormal deposition in bones called mineralisation 5. Calcium also has a vital role as a primitive molecular messenger and this has been utilised in the development of anti-hypersensitivity drugs called calcium channel blockers. Disruption to the calcium metabolism caused by lack of vitamin D can have serious effects on health. Experiments carried out by the Royal Navy at Gosport have shown that only eight weeks of living indoors (in relatively low illuminance environments compared to outdoor illuminance) can reduce calcium levels in the bloodstream of healthy men by 50% 6 and cause a number of other health problems. In this country studies have shown that in winter schoolchildren have less than half the vitamin Din their blood that they have in summer, and that even more seriously, people over sixty five may have levels throughout the winter that are less than half that of school children

5.

Unlike those in the United States, food producers in the

UK are not required to add vitamin D to their products. This makes daylight produced vitamin D even more important in maintaining the population's health. Although we still call it a vitamin , the active form of vitamin D is in fact a hormone, similar to other steroid hormones . •

~l)ill()()Q_(Sf(l'IOI.

Y'L
.•a:i.oo

r~

9 10

10

11

12

13

14

15

10

10

10

10

10

10

10

10

11

12

13

14

15

16

17

Lux

16

Time period (hours)

Figure 2.25 The threshold analysis of the Average Occupant in the medium daylight factor building (Med 1-10)

Hourly percentages of readings (A) above critical thresholds.

..

,,. 100.00

100.00

90.00 80.00

%R

70.00

E3 %R>200

Lux

60.00

D % R>500

Lux

50.00 40.00 30 .00

•

% R>2500 Lux

•

%R>10K Lux

20.00 10.00 0.00 9

10

11

12

10

10

10

10

11

12

10 13

13 10

14

15

16

10

10

10

14

15

16

17

nme period (hours)

Figure 2.26 The threshold analysis of the Average Occupant in the high daylight factor building

2.3.6. Interpretation of results As a basis for assessing the relative performance of the building types it is useful to have an indication of what an optimum lighting regime would be for an average building occupant. Although an absolute optimum may well be the outdoor lighting regime, the fact that occupants have to be in buildings precludes this as an option. In an effort to approach a compromise, recent medical evidence has strongly

62

2. Investigating light exposure in buildings

indicated that exposure to bright light (>2500 Lux) in the morning followed by normal indoor light levels (approximately 100 - 500 Lux) for the rest of the day helps maintain the synchronisation between circadian and temporal time almost as well as a natural outdoor lighting regime. Buildings performance can be rated by comparing the degree to which this optimum is approached.

NGHT

ml N

t MORNING

···~

MIO:-IYAY

Figure 2.27 The solar orientation and fenestration of the high daylight factor laboratory.

From the foregoing figures we see that the Average Occupants in the three buildings experience dissimilar types of exposure. The average perceived light level in the high daylight factor building is 2.46 times higher than its medium daylight factor counterpart, whereas the low daylight factor building is only 0.26 times the level of its medium counterpart. This indicates at a fairly crude level that as one would expect, the low daylight factor office has the lowest perceived light level, the medium daylight factor office the next highest and the high daylight factor office the highest. Whether the building tends towards homogeneity or heterogeneity of the lighting environment can be rated using the Standard Deviation (R.M.S.) of the Average Occupants trace. The Standard Deviation of the high daylight factor building is 2.63 times higher than its medium daylight factor counterpart whereas the low daylight factor building is only 0.59 times the level of its medium counterpart. This would seem to indicate that the variation in overall perceived level of illuminance (Average) is not directly proportional to heterogeneity (Standard Deviation). 63


N

[II

NIGHT

\

M,ORNING

..•G

AFTERNOON

MIO-DAY

Figure 2.28 The solar orientation and fenestration of the medium daylight factor office building.

NIGHT

Ill N

AFTERNOON

I

MID-DAY

Figure 2.29 The solar orientation and fenestration of the low daylight factor office building.

64


Considering the variation in hourly average perceived illuminance against time, it can be seen that the Average Occupant in the high daylight factor laboratory starts the day with at 1008 Lux, peaks between 1.00 pm and 2.00 pm with 1581 Lux and then gradually drops off towards the end of the day finishing at the 420 Lux level, 588 Lux lower. The associated Average Occupant in the medium daylight factor office building experiences an overall increase in perceived illuminance starting at 121 Lux at 9.00 am, peaking between 1.00 pm and 2.00 pm with 724 Lux and finishing on 447 lux at 5.00 pm, 326 Lux higher. The occupant in the low daylight factor office building experiences very little variation from the 64 Lux at 9.00 am, peaking at 155 Lux between 1.00 pm and 2.00 pm to end at 56 lux at 5.00 pm., a negligible variation. The associated Average Occupant in the medium daylight factor building starts at 236 Lux, peaks at 499 Lux and finishes on 274 Lux, 38 lux higher. These patterns in light exposure are due to the orientation of the fenestration in the buildings (see figures 2.27, 2.28 and 2.29). These studies showed that the orientation of the fenestration had a highly significant effect on the timing of the light exposure of the occupants. This also has significance when considering predicting probable exposure using daylighting models.

65


2.4. Daylight factor surveys

2.4.1. Summary Having measured the facial illuminance of occupants in buildings, it is necessary to attribute the characteristics of their exposure both to the design of the building and their movement within the building. This allows the cause of the particular illuminance characteristics to be identified and the effect of the design of the

building to be differentiated from the occupant's movement through it. The degree to which building design influences occupant behaviour and vice versa is a complex and contentious issue and rests outwith the mainstream of this work. The purpose of this chapter is to establish correlations between measured light dose and measured horizontal illuminance. The most widely used method of characterising the daylight modification properties of a building is the average daylight factor. The daylight factor is simply the ratio of internal illuminance on a horizontal working plane at a specified height above floor level at a point within the building to the unobstructed horizontal illuminance at the same height above floor level outdoors, both being measured simultaneously. It represents the modification of the ambient external lighting conditions by the building. The average daylight factor is as the term suggests, the average of a number of ratios taken at a number of points distributed through the building. It is an appropriate measure for the purposes of this study since it deals with average occupants of buildings rather than individuals, with the objective of characterising the buildings as a whole.

2.4.2. Predicting retinal illuminance From the clinical evidence described in section 1.2.3 it is known that circadian phase entrainment is a visually mediated phenomena. It is the illuminance with in an occupant's field of view (specifically the retinal illuminance) that is the main input signal controlling the circadian cycle. For the purposes of modelling circadian phase shifting the issue arises of whether a prediction of horizontal illuminance for a location in a building is sufficiently representative of the retinal illuminance of an occupant at that point for the results to be meaningful.

It is common practice to predict illuminances in buildings for a horizontal working plane and there are numerous reliable methods of doing so. Calculation of the retinal illuminance of an occupant on the other hand is potentially, extremely difficult since it requires detailed information not only on the occupant's location and surroundings but also on their facial orientation in both the horizontal and the

66


vertical planes. Such data is necessarily highly specific, and furthermore it is not as far as can be determined readily available. It was recognised therefore that direct calculation of retinal illuminance would involve an effort inappropriate for the exploratory nature of this investigation and that an approximation would have to be made in the interests of computational expediency. In the first instance the possibility of using cylindrical illuminance for th is was considered.

It could be argued that an occupant's field of view is more closely aligned to the vertical than to the horizontal for most of the time and that in reality their retinal illuminance is dominated by the luminance of vertical or near vertical surfaces within the field of view. On first inspection this would suggest that a prediction of vertical illuminance would be more appropriate than one of horizontal illuminance. It would however tend to exaggerate the luminance of windows and be relatively insensitive to the luminance of overhead artificial lighting and roof lights. A counter argument can also be made that this is in fact not the case, particularly in offices where it is the luminance of horizontal surfaces such as desk tops, papers and the like which exerts a greater influence on retinal illuminance. Despite this, assuming that luminance from vertical planes does dominate retinal illuminance, the problem still remains of the orientation of the occupant's view within the vertical plane. An average, omni-directional representation of illuminance on vertical planes can be derived using cylindrical illuminance which may approximate orientation independent average, retinal illuminance. Baker, Franchiotti and Steamers 1 state that Cylindrical lrradiance (at a point, for a direction) ( Ee.z ; Ez) is the quantity defined by the formula: E,,,z =

~ J41t$rLesin E . dQ

where dQ is the solid angle of each elementary beam passing through the given point, Le its radiance at this point and E the angle between it and the given direction, which is vertical unless otherwise stated. is the radiant flux and the units of cylindrical irradiance are Wm-2. They go on to state that: "This quantity {cylindrical irradiance} is the quotient of the radiant flux of all radiation incident on the outer curved surface of an infinitely small cylinder containing the given point and whose axis is in the given direction, by tt times the area of the cross-section of that cylinder measured in a plane containing its axis. The analogous quantities cylindrical illuminance Ev.z and photon cylindrical irradiance Ep,z are defined in a similar way, replacing radiance radiance

Le by luminance Lv or photon

LP."

It would seem therefore that cylindrical illuminance may give an approximation of orientation independent, occupant, retinal illuminance. One might initially assume

67


that since the luminance (here L.) of surfaces is easily derived from their illuminance and the relationship between cylindrical illuminance and horizontal illuminance is essential one of transformation through 90 degrees, that cylindrical illuminance may be derived relatively easily from the same information required to calculate horizontal illuminance. However, closer examination reveals that deriving dQ and

E

involves detailed calculation of inter reflection from internal surfaces, a

computationally intensive task not required in the simpler, split flux method of horizontal illuminance calculation described later in this work. The questions arise, firstly whether or not the considerable increase in complexity of calculating cylindrical illuminance is justified for the purposes of making general recommendations for a broad range of generic building types? Secondly, is the little used measure of cylindrical illuminance an appropriate measure for comparison of task illuminance in office buildings for instance? Increasing the computational complexity of predicting daylighting in buildings can be justified if the results lend significantly to the outcome and that the same conclusions could not be arrived at by simpler means. It is suggested that in an ideal case, cylindrical illuminance may offer significant advantages in representational accuracy over horizontal illuminance when simulating retinal illuminance alone, if in the future it is found that the luminance of vertical surfaces does in fact dominate retinal illuminance. However, when calculations of indoor illuminance are intended to be used to asses both circadian phase shifting in occupants and the general daylighting environment within buildings (for instance for task illuminance) then horizontal illuminance, although perhaps less representationally accurate for retinal illuminance, may have a wider acceptability and relevance. Furthermore, it is suggested that for the purposes of comparing alternative building designs, horizontal illuminance alone is a sufficiently reliable approximation of the probable relative difference in the average retinal illuminance of typical occupants in different building configurations. Given the uncertainty as to the dominant characteristics of retinal illuminance added to the difficulties involved in calculating cylindrical illuminance, horizontal illuminance has been adopted as the most appropriate (and calculable) measure of daylighting for the purposes of computer modelling described later in this work.

2.4.3. Measurement of daylight factors In order to examine the correlation between the facial illuminance (Light Dose) of an average occupant for a building and the average horizontal illuminance for the same building the average daylight factors for the three survey buildings were measured. This was done by dividing the floor plan of each building into grid

68


squares of approximately 3m2 and taking simultaneous measurements of horizontal illuminance at 1m above floor level at the centre of each grid square and a measurement of unobstructed external horizontal illuminance from the roof of the subject building. As can be seen from figure 2.30 there appears to be a good correlation between average daylight factor and the median of the average occupant light dose across the three buildings both in magnitude and direction. This gives confidence that average daylight factor is an appropriate indicator of

relative differences of the median of average of occupant light dose.

1000

.,

100

~~

rn rn mm~~~~~~~~ g ~ ~~ ~ ~ ~ ~ ~~ ~ ~~~~~~~~~~ ~~ ~ ~ : 1 oo ..__ _ _ _ _ _ _ _ _...,

···-------------------·······-······-------·-··-· ------------------------------------------------·

Oi

"

I/)

- • -Average Daylight factor (%) -

"' 0

..J

·-------I""--

-~.631

rn

.... a - Average Occupant light Dose (L u x )

mm'" m ="'''"'"" : : : :: :: : : """"mm :: . ------------------------------------· -- -;-;:we·--- --- --:~·:i:g:o::::::::: ::

--------···------------------------ ----------·

:::::::::::::::::::::::::::::::::::::::::::: •• ::: 2.324 1

High D. F. Building

I

I

I

Medium

Medium

Low D.F.

D.F.

D.F.

Building

Building

Building 11-20

HO Building

Figure 2.30 Correlation between Average occupant light dose and average daylight factors for the three buildings.

Unfortunately the measurements of horizontal illuminance can not be directly compared with light dose because they were not taken simultaneously, cross checking of mean cylindrical illuminance derived from the measured horizontal illuminances with the light dose was therefore not possible. However it would be a relatively simple exercise to measure horizontal and facial illuminance simultaneously in future.

69


2.5. Assessing occupant behaviour patterns 2.5.1. Summary The effect of occupant movement on light dose is recognised and in order to facilitate future predictive calculation existing data are presented to describe the percentage periods of time spent in various tasks by clerical and managerial office workers.

2.5.2. Data on occupant behaviour It would appear that average occupant light dose is very closely related to average horizontal illuminance for the three buildings surveyed. This can perhaps be attributed to the methodology of the surveys where considerable efforts were made to ensure that: 1) The occupants chosen were based at one particular workstation for the duration of a working day with departures from that position being very brief, or if longer (say for lunch or coffee) that they were scheduled and therefore attributable. 2}The distribution of the occupant's workstations through the buildings were relatively even, thus avoiding bias to one particular part of the building which may have physical characteristics (say glazing to floor area ratio) that differed substantially from other parts. 3) The orientation of the subjects workstations (and hence fields of view) were random with no overall bias to any orientation within each building. These measures were taken to negate the effects of unpredictable occupant behaviour (change of bodily location and change of facial orientation) upon the average occupant light dose. Outwith controlled conditions like these, individual occupant behaviour can be very variable. It depends entirely upon the working practices of the occupants as to how much time they spend at their workstations and also how they work at their workstations and if they use their workstations at all. If The working practice diverges from an assumed norm then accurate estimation of location may be difficult. For the purposes of characterising occupant behaviour for this study it has been assumed that: 1)

Occupant bodily location is specific to a particular area within a building that is related to a particular task. e.g. writing and telephoning are conducted at a workstation, printing is done at a photocopier and tea and

coffee breaks are taken in a defined area and so on. 2}

Facial orientation is omni-direction and is vertical.

Some data are available

1

on percentage time spent on office activities. These

data will form the basis of assumptions of normal occupant behaviour patterns for the purposes of this study. Unfortunately the data are not time specific, they do not

70


give indications of what time of day one activity is more likely to be carried out than another. Activities of managers and the precentages of the working day spent on them. (Taken from Bauwphysica). 5.00%

3.00%

•

Discussion

D Writing •Dictation • Calculation

C Proof-reading 50.00%

C

Reading

•

Post & copying

•

Information storage & retreival

• Telephone •Transport 10.00%

•Other

Figure 2.31 Example of activity pattern data available for the study. The data were derived from observation rather than self assessment by occupants making them in general more reliable. Activities of managers, from Lindegard and Horickson 1992, Bauwphysica.

It was not possible to record the location of occupants within buildings during the course of measuring their light dose. Although techniques for monitoring occupant location and facial orientation were proposed by the author they were felt to be too costly to implement for their limited benefit to the study in hand. As a matter of record it was proposed to place infra red emitters sourcing a coded infra red pulse once every 20 seconds in each room of a building. Each emitter's coded pulse would be unique. Each occupant wou ld be equipped with a small infra red sensitive lapel badge with a small solid state memory that would sense and digitise the coded pulses and store them in memory to be downloaded at the end of the monitoring period. It was proposed that the emitters and sensors might be based on I.A. television remote control handsets. To record facial orientation it was proposed that a small magnetic flux-gate compass be mounted on a headband (similar to the photosensor for the light dose surveys) and the output directed to a small solid state memory. Care would have to be taken to negate the effects of non-terrestrial magnetic fields . Despite not attempting to record occupant location directly an alternative possibility for future development was noted. Characteristics of the light dose trace can show when occupants enter or leave different zones of the building by marked increases or decreases in background illuminance. One example of this was termed the "coffee factor". In the high daylight factor building, the coffee room was in the basement and the

71


level of illuminance was relatively I.ow. A characteristic drop to this level of illuminance was observed in many of the subjects at 11.00 am and 3:30 pm, the times when they had their morning and afternoon coffee breaks. Similarly, periods spent outdoors at lunch time where characterised by very high background illuminances from 12:30 pm to 1:30 pm. The development of the concept of the average occupant however can make the need to pinpoint the location of real occupants within the building unnecessary. By characterising the average light dose of all occupants within the building we can examine the building as whole and its effects upon all occupants rather than specific occupants. Similarly we can refine our representation of the average occupant by defining subgroups based on their roles, for instance managers and clerical workers. The data on time spent in activities by various sub groups can provide a building independent characterisation of time to task allocation. This is not an unreasonable assumption as the data in figure 2.32 suggest. This can then be applied to individual buildings where groups of activities can be allocated to various locations within the building, e.g. photocopying to the print room, tea break to the canteen etc. Proportion of time spent at different locations by clerical and support staff

100

...

3

l1

90

u

-

4

0

•

At desk

70

0

Elsewhere in b uilding

60

D Elsewhere in other buildings in

80

organisation

Per cent 50

40 30 20 10 0

"

-

En11 mo 0 n A

B

;;t,,,

n

-

c

D

,., 8

Eo2 rl'.i:o E

F

•

Elsewhere in other organisations b uildings

0

Working at home

0

O ther

IiG

Buildings

Figure 2.32 Clerical workers are far more sedentary than managers or professionals. They sit at their desks for most of the working day. Clerical and support staff are also much more likely to sit at the least favoured places in the office. From the office environment survey Wilson and Hedge.

2.5.3. Building and occupant movement interaction However, this does of course ignore the crucial issue of building I occupant interaction and the effect of the bu ii ding itself on the activities carried out by a particular occupant, where those activities might be carried out, and the variation in individual occupant preference for activity location.

72


It has been demonstrated by a number of researchers 3 that there is a non-trivial interaction between the design of the building itself and the time dependent locational and activity behaviour of the occupants. For instance more social interaction occurs where casual visual and verbal communication can be made between occupants, in areas designed to be less rigorously demarcated into public and private areas. If control of aspects of the building such as blinds screens and workspace personalisation are given to the occupants then this will

also affect the way they use and behave in the building. There appears to be a complex feedback loop between occupants and building which is governed by the degree of control each has over the other. The complexity of this issue is beyond the scope of this investigation and it is considered sufficient to assume general trends for populations of occupants and if necessary for specific individuals based on the data available. It is inherent in the process of generalisation that a diminishment of individual accuracy is incurred in favour of clarification of general trends. The author would suggest that the detailed investigation in future of the complex dynamic interaction of occupants and buildings could yield results which may significantly enhance the performance of future building designs.

73


2.6. Assessment of circadian phase shifting 2.6.1. Summary Having measured the light dose of some occupants, quantified the daylight modification properties of the buildings by measuring daylight factor and considered the representation of occupant behaviour and its effect on light exposure, it remains to measure the cumulative effect that these factors have

upon the circadian cycle of the occupants. This is crucial to the validity of the thesis which rests upon there being a demonstrable and causal link between variations in occupant light exposure in buildings and variations in their circadian cycle. The physiological and psychological evidence from other research fields supporting such a link has been described at some length in the foregoing chapter. However, it has not been demonstrated that the variations in illuminance caused by the design of buildings experienced by building occupants actually causes significant variations in their circadian cycle. Consequently it has not been shown that if such variations in circadian cycle did occur what effect they would actually have on the health and comfort of the building occupants. In order to address these questions two methods have been developed to assess: 1)

The variation of occupant circadian phase caused by the light dose they experienced in the building.

2)

The occupants self perception of their comfort and health during the course of the light dose survey.

Unfortunately it was not possible to use either assessment technique during the Cambridge light dose surveys consistently, so direct correlation between measured circadian phase shift and light dose and also occupant self perception of health and comfort could not be made. However the techniques have been refined since and are presented here as techniques that may be used in future work.

2.6.2. Measuring circadian phase To measure the circadian phase of a biological clock one must be able to accurately record its output. Most behavioural, physiological, and biochemical variables in animals show circadian rhythms, but there are considerable problems in determining which rhythm is the output of which pacemaker and how accurately each rhythm reflects the clock's behaviour. A fundamental problem is that in no case has the exact biochemical or biophysical structure of a circadian clock been 74


identified. Certain cells or groups of cells can be identified which appear to contain circadian oscillators, but clinical researchers are some distance from a complete understanding of their mechanism. Ideally we would monitor the clock directly, although we would be content to monitor any rhythm that accurately represents the behaviour of that clock. Isolating circadian phenomena from the effects of other exogenous stimuli other than light can in practice be difficult. The rhythm that is measured is the product of both the circadian clock and direct random influences from the environment. For example, humans have a welldefined body temperature rhythm that is actively generated by endogenous circadian clocks 2. The rhythm has a maximum during late afternoon and a minimum in the early hours of the morning. Nevertheless, a hot bath at any time of day or night will directly cause a rise in body temperature that may alter the observed body temperature rhythm and thereby obscure experimental measurements of the clock's behaviour. Any strategy of measurement must isolate circadian phenomena from other events. Commonly measured indicators of circadian phase are: 1) 2) 3) 4) 5) 6)

Sleep and wakefulness Feeding and drinking behaviour Thermoregulation Endocrine function Renal function Reproductive function.

Of significance is the fact that not only does the circadian timing system control the basal level of physiological systems, it also influences the responsiveness of each system to challenges at different times of day, particularly as has been previously noted, mental challenges and the ability to cope with stress situations.

2.6.3. Circadian variations in mental efficiency The efficiency with which many kinds of mental tasks are carried out varies considerably, in a systematic manner, according to the time of day or night at which the task measurements are taken in synchrony with the basal circadian cycle 3 and other markers of circadian phase such as sleep and wakefulness and thermoregulation 4. The evidence presented by Colquhoun and Kleitman demonstrates that in many cases, performance at certain kinds of task exhibit marked circadian periodicity, which appears, in general to be in phase with the concurrent rhythm of body temperature. This is supported by work by Blake 5 which supports very strongly the notion that time of day task efficiency effects are the effects of variations in sleepiness or arousal during the day induced largely by

75


the circadian cycle. Furthermore, the effects of exogenous stimuli such as mealtimes and ambient temperature are reported to have a significantly reduced effect on the overt circadian rhythm measured in this way than say the measurement of a physiological marker such as blood cortisol level. Because invasive techniques such as core body temperature or blood cortisol level measurement are not administratively suitable for surveys of building occupants it is convenient and most useful to adopt a non-invasive method such as mental task efficiency.

104

98·5 I I

I

I

I I

102

I

/

I \..--,

I

V>

/\

I

I

u..

I

1-

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w w

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a:

\.)

I

w

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0

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I I I

\

\

I

I I

I

100

I

\

w

0:: w

/

I

z

u

a..

I

98

', I ..J

,,IPercent

r:n-s~~-~-~-"~~-- % 0

4

8

12

16

20

24

HOURS

Figure 2.34 An illustration of the inverse relationship between mental task efficiency and oral temperature. Variations in group mean oral temperature taken at the hours of test administration shown on the abscissa, and concomitant variations in group mean time required to name 600 colours, the latter expressed as a percentage of the total group mean score for the period. From Kleitman and Jackson, 1950)

Mental task efficiency performance exhibits a diurnal curve, consisting of a progressive decrease in Reaction Time (RT) during the morning and early afternoon and a rise in the late afternoon and evening and correlates closely with the inverse of the basal circadian cycle measured by core body temperature and with measures of sleepiness 6. The Endogenous circadian phase maximum (ECP max.) as measured by core body temperature corresponds with the ECP minimum (ECP min.) as measured by mental task efficiency. Although by no means perfect, measuring mental task efficiency is widely regarded as a normally reliable noninvasive marker of circadian phase and is felt to have sufficient resolution to make it appropriate for the purposes of examining daylight mediated circadian phase shifting in building occupants. The wide variations in indoor illuminance measured during the light dose survey gives confidence that there is sufficient variation in perceived illuminance to cause a circadian phase advance or phase retardation of small but measurable proportions. As has been previously described, illuminance of as little as 500 Lux has been shown to have significant resetting effects on the circadian cycle. Much larger differences in average illuminance between the high daylight factor and low daylight factor buildings have been measured, on average 620 Lux. Therefore one might reasonably expect to detect some variation in the 76


Respondents self assesment of lethargy symtoms over a 6 week survey period Mon 27 June 88 - Sun 7 Aug 88 100

90

- - - - -week1

80 -----Week2

70

--·-·-·Week 3

60

Per cent 50

- ·-·--Week4

40

-------- Week 5

30

week6

20 - - - Average

10 0

Mon

Tue

Wed

Thu

Fri

Sat

Sun

Day of the week

Figure 1.14 During a detailed survey of a sick building carried out in the summer of 1988 respondents were asked to fill in a diary of their symptoms on a day-to-day basis. Here are some of the results for the lethargy symptom. The daily data for the 42 days of the survey have been superimposed on a week-by-week basis to bring out the patterns in the data. Weekly patterns for virtually all symptoms peak on a Thursday, falling off rapidly on Friday and Saturday. The point to note here is not that people get more lethargic as the working week goes by, but the levels of lethargy, especially on a Thursday afternoon, which can be twice as high as at other times during the working week. As other symptoms show similar patterns, it is likely that other behaviours will be adversely affected. The survey was carried out by Building Use Studies Ltd. in association with Thomson Laboratories and the Ove Arup partnership, working under contract to the Building research establishment. The ' healthiest ' and 'unhealthiest• buildings compared (u sing t he building sickness score as the criterion of health). Dala collated In the ·omce Envirooment Survev• bv Buildina Use Studies Ltd. Londoo 1987.

I

I

J, All bMlllllD!ll" lbl bHllbl1151 Buildlna !Code Numbe

Slcknua Score

Oraanisatlon

Ventilation

81 141 21 53 151

1.25 1.52 1.53 1.54 1.63

Private Private Private Private Private

Mechanical Mechanical Natural Natural Natural

Humldltv Controls

. .

Ooenable Window•

Tinted Glazing

Aae

% Person• in 1·2 Person Olllces

% clerical s t all

Yes Yes Yes Yes Yes

No No No No No

1980's 1980'5 1950's 1960's 1920's

95 90 80 20 65

22 43 73 38 23

Yes Yes No

No No No

1980'5 1980's 1980'$

50 30 90

27 14 60

No No No No No

Yes Yes Yes Yes Yes

1970's 1970's 1970's 1970's 1970'$

12 20/ 30 9 1 1

23 60'40 45 93 86

2. Ale '51ndltl11atll 11MlllliD91• lbl bHllbllll 2 11 51 25 1 13.

411

2. 12 2.25 2.6 n .••

161 102 41 293 291

Table 1.3

Private Private Private

VAV VAV VAV

Steam Evennratlve

lthu 4.25 4.29f 72 4.76 4.91 5.08

Public Public/Private Public Public Public

Induction Induction VAV Induction CAV

Sorav Snrau Sorav Snrav

Results of class studies of generic building types, their physical design attributes and

the reported sickness score associated with each.

Reported cases suggest that it is most prevalent in air-conditioned buildings, though the evidence tends to rest on one-off cases, with no controls for the

29


purposes of comparison, or controlled but nevertheless small samples of buildings. Finally, Building Sickness has been reported in most Western European countries, in the United States and Canada. All these countries have a large stock of office buildings that are often air conditioned and artificially heated and cooled. Cases of building sickness in office centres in the far east and the southern United States,

where air-conditioning systems are used for the most part to cool, not heat, have not as yet been reported 19. Significantly these areas are at a lower latitude than much of Europe and north America. It is not immediately obvious from the predominant characteristics of the syndrome listed above what effect daylighting might have on its occurrence. However closer inspection of available data reveals a potentially significant correlation between the daylighting environment of office buildings and the satisfaction of office workers with their overall working environment. Furthermore, interpretation of these data may account for: 1) the prevalence of lethargy as the predominant symptom 2) the consequent loss of productivity 3) the increase in occurrence of the symptoms during the working week 4) the higher incidence of complaint amongst clerical staff 5) the symptoms being more common in the afternoon 6) the concentration of SSS in northern latitude office buildings.

1.3.3 Hypothesis From the evidence provided by studies of human circadian rhythmicity and SAD it is plausible that if the day to day lighting regime of occupants working in a building was such that it induced circadian phase shifting that was not synchronous with temporal time rather than entrained to it, then such desynchronisation may have a number of effects that could be significant contributory factors in the occurrence of 'Sick Building Syndrome'. The symptoms could reasonably be expected to be more severe in occupants who are predisposed to a greater or lesser extent to some form of SAD (as many as 1 in 4) but need not be restricted only to that

group. While the severity of depression, mental fatigue, lethargy and inability to handle stress experienced by predisposed SAD occupants may not be evidenced in the remaining normal healthy adults, this group may still experience temporal desynchronisation and untimely drowsiness (as circadian phase shifting experiments have shown) sufficient to impair their perception of their working

30


environment. Furthermore, reduced energy levels in all occupants may heighten their sensitivity to "background" environmental stressors such as indoor air pollution which although the pollutant concentration is not above normally acceptable limits as SBS surveys have shown, in situations of occupants having their sensitivity heightened by circadian phase desynchronisation they could be above tolerable limits for individuals. How would circadian phase shifting in building occupants work? There are at least two possible scenarios in which a circadian phase shifting effect could operate in buildings. Consider the variation in illuminance perceived within the field of view of an individual working in an office building. It is likely that they spend a large proportion of their time in the building experiencing relatively low levels of illuminance, punctuated by shorter periods spent outdoors or close to windows where they may experience very much higher levels of illuminance. This occupant would experience a lighting regime similar in many respects to the low illuminances (indoors) and high illuminances (outdoors) simulated in the circadian phase shifting clinical trials previously cited. It is therefore not unreasonable to suppose that the lighting in a building could alter the timing of an occupant's circadian cycle in the same way that these experiments did. This could be described as an "active" intervention in the circadian timing system. If a particular combination of building design, lighting design and occupant behaviour pattern produced a lighting regime which advanced or retarded the cycle sufficiently to alter mood, induce drowsiness, sleep disturbance or mental fatigue, then the wellbeing of the occupant would be materially and perceptibly affected. Such an alteration need not be large and could conceivably be incremental over a period of time. This may be evidenced by the available data on the weekly repeating pattern of lethargy in Sick Buildings which shows a general increase in lethargy during the week and a sharp drop during the weekend when occupants are not present in the building. A second possibility is that an individual experiences insufficient illuminance to have any light mediated phase shifting effect at all. The circadian cycle has a natural period of approximately 25.1 hours and unless it is regularly 're-set' by sufficient light at the correct time, an individual's physiological functions will retard in relation to temporal time and his or her perception of the elapsed time will slow down. This can be described as 'passive' intervention in the circadian system and has been demonstrated by Siffre and Mills in a series of light deprivation

31


experiments in caves and compartments. It is not unreasonable to suppose that if a relatively low illuminance, homogeneous lighting environment were to have insufficient effect on its occupants, then the resultant desynchronisation of circadian and temporal time may have a malign effect on their well-being and their perception of their work environment and productivity. Either of these two methods of circadian phase shifting could conceivably contribute to a 'sick building' by actively resetting the circadian system to be significantly desynchronised in

relation to temporal time or by passively allowing the circadian system to let itself become so. Conversely, only active intervention could reinforce the impression of a 'healthy building' by resetting the circadian system by just the right amount to keep it in synch with temporal time. At the very least such a circadian effect, if not the principal cause of 'sick building syndrome' may at least heighten the occupants sensitivity to other factors which may be more important, such as indoor microbial and chemical air pollution, noise pollution and inability to control the environmental conditions. From the clinical evidence it is known that the required resetting of the unentrained circadian timing system is approximately +1.1 hours. This implies that total daylighting exposure after the Endogenous Circadian Phase maximum (ECP max) must exceed the total before ECP max by 1.1 hours. In practical terms for normal healthy adults this means a greater amount of daylight in the morning than in the afternoon and evening. If this were not the case one might expect to see occupant circadian phase delay (-ve resetting) such that the onset of the sleep phase of the circadian cycle was advanced to overlap into the normal working day. This could account for the higher frequency of lethargy and tiredness symptoms in the afternoon reported in Sick Building Studies. It has been widely assumed that the occurrence of SBS being restricted to higher latitude office buildings in the northern United States, Canada, northern Europe, the UK and Scandinavia and not the equatorial regions has been because of reduced ventilation rates to reduce heat loss. Another possibility does however arise in the light of evidence on circadian dysfunction. The frequency of occurrence of SAD symptoms in populations rises with increase in latitude. SAD is virtually unknown in the equatorial regions where there is little seasonal fluctuation in the diurnal daylighting cycle and the intensity of available daylight illuminance is consistently higher. SAD as has already been described is most widely reported at higher latitudes where there is considerable fluctuation in day length with the seasons and where daylight illuminance can be relatively low compared with equatorial regions. It is plausible that it is the variation in daylight availability with

32


latitude, exacerbated by particular kinds of building design, that could trigger the higher incidence of SSS symptoms reported in northern latitude buildings. It is significant that a commonly reported feature in the occurrence of 'sick building syndrome' is a homogeneous, and relatively low illuminance, artificial lighting environment. This is often the product of tinted glazing, deep plans and extensive, uniform artificial down lighting. 'Healthy' buildings, on the other hand, are often reported as having a varied lighting environment with a substantial natural

daylighting component. This is supported by the available evidence. As one might expect there is a strong overall correlation between occupants' close proximity to windows and satisfaction with their office environment as can be seen in figure

1.15. Windows and satisfaction with the office environment

y = 3.4816 - 0.71283x R"2 = 0.963

3.3

........i::v 0

-

3.2

IU

..... ....!U

1:1

r /}

3.1

Satisfaction

Highly dissatisfied=S Highly satisfied=l

CF)

3.0 2.9--~..----,.----.-~--.-~-.-~....-~..----.,...._--,..~-1

0.0

0.2

0.4

0.6

0.8

1.0

Proportion of staff sitting next to a window Figure 1.15 For six study buildings, the proportion of staff sitting next to a window is shown along the bottom axis and the mean score for satisfaction ratings is on the vertical axis. Proportions range from O (no staff next to a window) to 1 (all staff next to a window). Satisfaction is an average satisfaction score taken from all the satisfaction data in the survey (there were ten variables altogether including temperature, ventilation, noise, work surface, car parking and five others). A score of 1 is highly satisfied, and 5 highly dissatisfied. A score of 3 is the neutral point on the scale. The data show that the most satisfied staff sit next to windows, and that the relationship is a relatively strong one. There are, though, only six observations so further data need to be gathered to explore the relationship more fully. The diagram also includes 90% confidence bands. Satisfaction data were collected by Building Use Studies Ltd. Building evaluation data were

measured by DEGW Ltd.

The assessment of satisfaction included a number of factors related to illuminance and view to the outside as well as ventilation . It is necessary to distinguish between satisfaction due only to ventilation and satisfaction due to lighting and

33


view aspects of the presence of windows but unfortunately the resolution of the questioning within this particular survey was too coarse to detect this directly. However what can be presented is a body of circumstantial evidence to support the notion that the daylighting environment within office buildings has a direct effect on the occupants satisfaction with their work environment. Of particular use in this respect is data shown in figure 1.16 of the relationship between plan depth and occupant satisfaction. The general trend is for dissatisfaction to increase as

plan depth increases. Depth of space and percieved mean satisfaction y = 2.9354 + 7.0448e-3x R"2 = 0.695 3.4 ~------------------.

3.3 ~

0

v

"'i::

3.2

-~v .:l

·.:: "'

E

::l z 200

100 0 Senior managers

Managers & Senior clerical Professional

Clerical

Other

Total

Occupant type

Figure 1.18 Presence or absence of a window close to different occupant categories. There is a tendency for certain groups of office workers to have favourable seats close to windows and for others not to, dependent on their peer ranking within the organisation.

It is common practice with large organisations to give management workstations and offices close to windows and to give clerical and administrative staff less

35


favourable positions further away from windows. This is borne out by the data shown in figure 1.18. Significantly, dissatisfaction with the working environment is most often reported by clerical staff and it is they as we can see who are most often furthest removed from windows in the less well daylit parts of buildings. Conversely, fewest symptoms are reported by managerial staff who most often have workstations in

close proximity to windows. Again this seems to suggest that there may be some attribute of windows which reduces the incidence of reported SSS symptoms. This notion is further reinforced by the data shown in figure 1.19. There is a strong positive correlation between control over the daylighting through windows and the number of reported SSS symptoms. The more control over daylighting occupants have the fewer reports of symptoms there appear to be. Correlation between number of symptoms and occupant perception of control over lighting

100 90 80 70 60 Per cent of people

60

•

50

O Neutral

40

• Full

None or little

30 20 10

0 None

1 to2

3to5

6+

Overall%

Number of symptoms

Figure 1.19 The correlation between the number of reported symptoms and occupant perception of control over the lighting environment.

The general issue of occupant control over their own environment is one that consistently recurs in the SSS literature. It appears that not only control over daylighting within buildings but also temperature, noise and defensible space are important issues to occupants and significantly affects their self perception of their

work environment. Dissatisfaction with the office environment appears to be exacerbated by the fact that many office buildings are designed in such a way that the occupants have little ability to control their environment. A minority of office workers in 'The Office Environment Survey" perceived themselves as having partial or full control over temperature. There was a strong correlation between the

36


occupants perceived control over their environment and their perceived productivity as shown in figure 1.20. Control and productivity for temperature, lighting and ventilation in the office

10

8

I

6 More or less productive than 4 average

2 ...

0

·2

_

.... _

....

_,..../ ,.-- ., r-.,~'....

~-· r:,,_ __ , , ' r~-.L-W"'~ ----~

"""""~··

I /// I

~----

___...,....

"

/ ---Temperature

, ,,,

-----Ventilation

~"

... -.. ' ,/

------·· Lighting -·----Overall Control

/

.-

_. - ..... i.

I

Degree of control (low=l, hlgh=7)

Figure 1.20 Control and productivity for temperature, lighting and ventilation in the office. One of the most prominent features of the "Office Environment Survey" was the importance of control to building users. The less control people have over heating, lighting and ventilation in their offices, the more likely they are to show losses of productivity and to complain of ill health. In the survey, respondents were asked in separate questions about their self-assessments of their productivity at work and the degree of control they have over the office environment in the immediate vicinity of their work area. The results show that the more people report that they have control, the more likely they are to think that they have higher productivity. The relationship is strongest for control over temperature, as one would expect, with ventilation and lighting showing similar, but less strong, associations. People were also asked about their overall control over their environment. Here, as control rises, productivity goes down at first but then rises again. It seems that it is better to have a lot of control, or little control, but not a mixture of the two.

Factors which appear to add to the risk of building sickness divide into two broad groups: 1)

Those that create a poor environment, measured in terms of prevailing and well-established user needs (physiological, practical and psychological).

2)

Those that reduce an individual's tolerance threshold of poor conditions.

It is possible that tolerance thresholds are reduced in many air conditioned buildings because the occupants are less able to exert personal control over those conditions. Simple mechanisms to improve comfort - opening windows, turning off the sound of a fan , adjusting an effective thermostat - may not be available to them.

37


It is also possible that many air conditioned buildings are oppressive because they block out some psycho-physiological perception of a sense of the "outside"; it is notable that the three buildings that qualified in the "Office Environment Survey" as healthy, had clear rather than tinted glass, and two had windows that could be opened. The "Office Environment Survey" concludes with a comparison of the design of most and least healthy buildings as their occupants perceived them. All the healthiest buildings varied in age but all had mechanical or natural ventilation,

and all had opening windows and untinted glazing. Even two out of the three healthiest air conditioned buildings had opening windows and none of them had heavily tinted glazing. The least healthy buildings were all air conditioned , natural light was restricted and the artificial lighting was highly uniform. The report concludes by emphasising the concept of personal control by the occupants over the environmental parameters they are subject to. Whether these are built-in controls to modify the climate or merely the possibility of the person to move around the building into different environmental zones are not differentiated. Particular problems that are outlined are: 1)

Sealed windows or windows which it is not practicable to open, such as large windows in high buildings

2)

Mirrored glass and tinted glazing which distort the perception of outside conditions and so prevents people from being able to "read" and "respond" to them

3)

Building depths which necessitate a reliance on artificial light, which inevitably offers a much reduced range of possible lighting conditions and which means that occupants are unable to "rest their eyes" by looking outside.

Aside from the data from SBS studies other work is available which supports a correlation between occupant perception of the internal environment and proximity to fenestration. Work by Verdeber 31 into the human response to daylighting in the therapeutic environment has shown a subset of results from an empirical investigation on human response to key functions of windows. Daylighting was found to be one of an array of twenty cognitive dimensions of windowness in the therapeutic environment. Among the findings, therapy treatment rooms whose windows allow for daylight penetration were perceived as desirable by patients and staff alike. Respondents ascribed highest preference levels for dimensions whose contents addressed interesting views. Daylighting was of second highest priority, whereas, on the opposing end of the spectrum, dimensions labelled "Architectural Windowlessness" and "Psychological Windowlessness" denoted

38


conditions characterised by a complete lack of daylight transmission and total dependence on artificial illuminance; these indices were little preferred. The author concluded that the human dimensions of view and daylighting relative to emerging energy-conscious daylighting strategies should receive greater consideration within the design process. Extensive psychological research on personnel on Antarctic bases by Taylor 32a, Bizyuk 32b, Deryapa 32c, Holmes 32d and Lugg 32e has shown that daylighting and view have a profound effect upon their well-being. Measurable variations in working output and accuracy have been reported in tests varying window size and view. Paliwoda

33

has carried out research on occupant

preferences for window shape in the Arctic when window sizes are restricted to reduce heat loss. His findings indicate that a narrow horizontal window giving as wide a field of view as possible was given the greater preference rating by his subjects. Work carried out upon preferences in lighting by Ne'eman and Hopkinson 34a, 34b has established that the subjective responses of office workers corroborate the widely held view that direct daylighting, for whatever reason is preferable to artificial lighting. They have also examined the empirical relationship between glazing area, room depth and user satisfaction and have shown that satisfaction with window size increases until the window width reaches about 30% of the wall width. Beyond this Hopkinson has reported that, windows become less satisfactory from a psychological point of view, giving rise to complaints about lack of privacy and glare problems 35. A similar survey carried out by Keightly 36 found that the lower limit of satisfactory glazing area was approximately 20% of the area of the window wall. It is interesting that the result of Keightly's study was similar to that of Paliwoda in that a small but very wide window was considered acceptable even if the overall glazing area was less than 20%, suggesting a preference for a wide lateral view. Meerdink and Witteveen 40 have produced revealing work on the correlations between assessment and acceptance of daylight and view and the physical factors such as surroundings and activities which determine light and view exposure. They have introduced a new concept of daylighting dynamics to describe this interrelationship and have established a tripartite composition for it, consisting of internal dynamics, external dynamics and task dynamics. Work carried out by Markus 41 draws similar conclusions, namely that windows are critical for office workers' satisfaction, and that the ideal window should provide a three component view of sky, city-scape and ground. Wilkins and Nimmo 37 have established directly measurable relationships between artificial lighting, V.D.U.s, headaches and eye strain. The main thrust of their research has been to show that low frequency flicker in both fluorescent lighting and cathode ray tubes causes the eye to overshoot when aligning itself to focus on an object. Experiments were carried out on a subject's ability to read text under low

39


frequency flicker conditions and conclusive proof was obtained which showed that the extra time the eye needed to re-align itself to be able to read and focus, reduced its efficiency and caused muscular eye strain and headaches. Hughs 38 has experimented with simulated natural light (produced by high-frequency fluorescent tubes) in underground environments which also have temporal disorientation problems associated with them. Like many other researchers both in psychology and physiology, he has found that full spectrum light applied to

subjects at a level of 2000 Lux for periods of up to two hours during "outside" daytime can be used to minimise the psychological effects of prolonged periods spent without the diurnal cycle. He has not indicated the effects of altering the timing of the light exposure, to examine for instance whether morning, midday or evening exposure is better. The use of artificial full spectrum light to provide a regular diurnal lighting regime in northern Canada by Hellekson, Kline, Rosenthal and others suggest this has had a beneficial psychological as well as physiological effect. Like Hughs they have used full spectrum fluorescent lighting of around 2000 lux but in this case to reset the internal clocks of seasonally depressive patients. Kendrick's work on daylight variability in rooms 39a, the dynamic aspects of daylighting 39b and the contribution of daylight and sunlight to healthy buildings 39c

have established a number of qualitative concepts which seem to hold true for

most buildings and people. It is significant that these concepts seem to be born out to a large extent by the available physiological and psychological evidence. The preceding evidence of the relationship of daylighting and particularly fenestration and plan depth to the reported incidence of symptoms of Sick Building Syndrome and occupant perception of the quality of the internal environment gives confidence that at the very least there is little significant conflicting evidence to show that daylighting in buildings does not have an effect on the health and wellbeing of building occupants. On the contrary there is much evidence, some of which has been presented above to show that there may be a significant relationship between the characteristics of daylighting in buildings, and increased incidence of SBS symptoms. However it is recognised that it is inevitable that many of the correlations in this hypothesis are necessarily circumstantial simply because the available data on which they are based was not acquired specifically for the purpose of its proof but for other purposes. The presentation of this hypothesis and the evidence in support of it is intended only to make the case for the plausibility of a connection between SBS and SAD. The purpose of this thesis, as has already been stated is as pilot study and as such is intended to develop methods that might be used in further work to establish whether or not there is actually a substantiated connection. It is not intended to conclusively prove or disprove the validity of this hypothesis but only so far as time and resources have 40

1. Bulldings lighting and the biological clock

allowed to present the results of research work providing further original evidence in its support and at the same time describing the techniques used in their acquisition. In order to develop these issues beyond the circumspect analysis of existing data it has been necessary to: 1) develop methods of measuring the "light dose" of occupants in buildings to determine whether or not the illum inance within an occupant's field of view is of

such a type that could induce circadian phase shifting. 2) to use these methods to collect detailed data on occupant light dose from different generic building types to determine if there are significant differences in the light dose that differing generic types cause occupants to receive. 3) to relate those measurements of light dose within the occupant's field of view to more easily predictable measurements of horizontal illuminance and assess the correlation between the two. 4) to assess from existing data typical occupant behaviour patterns for particular building types in terms of percentage periods of time spent in particular locations or carrying out location specific tasks. 5) to propose a method that may in future be used to assess directly without estimation the actual circadian phase of occupants in buildings by non intrusive means. The following chapter deals with these issues and describes methods that can be used to develop the hypothesis.

41


2. Investigating light exposure in buildings 2.1. The photographic light dose meter 2.1.1. Summary Two methods of gathering data on the variation in illuminance of an individual

working or living in a building against a time dependent (what shall be referred to as Light Dose) were developed. The first was a low cost photographic method to assess the feasibility of carrying out large scale surveys of many building occupants simultaneously. This was considered useful (if in the future) it proved necessary to undertake large surveys. The second was a more elaborate but ultimately more accurate method of monitoring the light dose of only two occupants simultaneously, intended for the purposes of this research.

2.1.2. Measuring light exposure Because circadian rhythmicity is a visually mediated phenomenon, the way in which the causal light exposure is measured is particularly important. For the purposes of discussing and measuring light exposure, it is useful to note some practical differences between horizontal and vertical illuminance. It is conventional to measure the ambient light level on a horizontal plane facing upwards. What is normally experienced by a building occupant is the illuminance on their face which is more often closer to the vertical plane than to the horizontal. This is particularly important in measuring perceived Hght levels. This perceived illuminance is highly dependent on the luminous excitance of the surfaces within the field of view, their disposition in space and the azimuthal orientation of the observer. The attitude and orientation of the occupants head further divorces the actuality from an assumed norm of either horizontal or vertical. It is assumed that there is a close correlation between facial and retinal illuminance, although this is by no means certain. Measuring retinal illuminance is difficult whereas measuring facial illuminance is re latively straightforward. For this reason the latter method was adopted. For the purposes of study related to circadian rhythmicity it is therefore crucial to measure the light level an.occupant actually experiences around their eyes and from those sources that are actually within their field of view. The issue of spectral composition of perceived light is one that further complicates derivation of cause and effect. Whilst an artificial source may produce the same total radiant fl ux as daylight from a window, it does so in different wavelengths. We perceive this as variation in colour. Because the human eye is selectively sensitive

42


to the frequencies of visible electromagnetic radiation , there is likely to be a difference in perceived luminance between two sources emitting the same radiant flux but having different spectral compositions. The sensor used to measure perceived illuminance must therefore have a spectral sensitivity close to that of the human eye.

2.1.3. Description of the dose meter The first method of measurement that was developed was a photographic method of recording the light dose for an individual. It was based on the pin-hole camera principle and although simple in construction it had a number of advantages over other more complex design options. It was built from one, inexpensive electric wrist watch mechanism and casing. By utilising readily available photographic material and simple mechanical components, costs were kept to a minimum. It was recognised that the ability to monitor a subject's light exposure during the course of a day, cheaply and by a convenient method would make large scale, simultaneous surveys of occupants feasible within the confines of a limited research budget. It was with this in mind that the Photographic Light Dose-meter was developed and tested in April and May 1989. The design of the photographic light dose-meter was based on a rotating disk of photographic film which was housed within a light-tight casing, into which was incorporated a slit aperture as shown in figure 2.1 . . ·. ~?_I.;'61~~ llASE PLATE WIT!-

''i/ '

3

POSITION OF OUTER . CASING

I I I

------PLAN

DIAGRAM OF A TYPICAL DISl\SHOWING

THE RADIAL BANDING OF THEfRACE.

N 8 . 11 IE BENCHMARK TRACE IN THE 12.00

HOURS POSITION (I).

SECTION

Figure 2.1

Diagram of the operating principles of the photographic light dose-meter.

The slit aperture was designed to minimise diffusion and divergence of incoming light so as to maximise the resolution of the trace on the disk. The design of the slit and aperture are shown in figure 2.2.

43


LlGHT

~~~~~

------------------~ 2 .-~~~.,..._

3.

_ _.

----l~-.~--------J~~

5.

1 2 3 4 5 6 7 8 9 1o 11

Optional filter Transparent window casing Light tight casing Recessed mounting box to give a 90 degree angle of view Opalescent acrylic diffuser Slit aperture in box mounting Adhesive fixing for slit film Slit film Photographic film disk Revolving base plate Slit.

6. 7.

9.

FILM MOVIKG IN THIS DrRECTIOlf l l.

Figure 2.2 Diagram of the slit aperture. The aperture in the prototype was 7.Smm long and approximately 50 microns in width and was made from a scored piece of photographic film. The slit rested close to the surface of the rotating disk which was positioned emulsion side up and the slit film emulsion side down, to reduce the amount of divergence. Light fell through the aperture onto the disk of photographic film in a narrow band and created a trace mark which became visible when developed. The rotating disk therefore created a radially banded sequence of traces on the film, which once developed indicated the light intensities that fell on the disk during the recording period. Note the method of fixing the slit film at one edge only. This utilises the film's natural springiness to ensure that the slit always rests gently on the moving photographic disk and accommodates any unevenness.

The disk rotated once every 12 hours and was of sufficient size to give a readable resolution of approximately 2 minutes over that period. The diameter of the photographic disks were 20mm of which the outer 7.Smm of the radii were used to record the traces. The disks were fixed to the rotating base plate by a small piece of double sided adhesive tape. The overall dimensions and the main components of the dose-meter are shown in figure 2.3. The motive power for the device was supplied by a standard battery powered, electric wrist watch mechanism. The slit aperture was recessed within the body of the device to give an 90 degree angle of view and all the internal and external components of the device were rendered matt black. The device was tested using Kodalith Ortho Film, Type 3 (ESTAR Thick Base). This film can be developed in safelight conditions and disks were easily made from sheets of the film using a simple die punch. Because of the films' spectral sensitivity, the red half of the visible spectrum will not register on the film (ie. will not create a trace mark). This does not invalidate the development of the device since it has little bearing on the operational principles being tested. The

44


compromise of using a film which did not register the entire visual spectrum was made for ease of cutting, loading and developing the disks. If a full scale survey were to be undertaken a film with a spectral sensitivity corresponding closely to the C.l.E. Standard Observer Curve would be used. This would necessarily entail cutting, loading and developing the film in complete darkness but this is not seen as a major problem if carried out on a large scale. LIGHT

1 2 3 4 5 6

26mm Figure 2.3

...

7 8 9 1O 11 12

Optional filter Transparent window casing Light tight casing Diffuser Scored film slit Recessed mounting to give 90 degree angle of view Photographic disk Rotating base plate 0-ring seal Drive shaft Watch mechanism Outer casing

Section through the photographic light dose-meter.

2.1.4. Operation of the dose meter Before locating the device on the subject, the loaded dose meter was placed under a standard light source (a 150 watt quartz halogen projector bulb) at a set distance {1 meter) for a set period of time (15 seconds) to produce a reference trace on the film to which later readings could be calibrated. This was necessary to overcome variations in the developing. A light meter was placed alongside the dose meter and a reading in lux was taken of the intensity of exposure. Most photographic films do not have a linear response, so a non-linear conversion equation must be used to convert the trace readings into lux readings. A calibration procedure may be carried out to relate film density to the amount of light needed to produce it but this is a laborious process. The manufacturers can supply equations for the linearity of most of their films at little expense and this was the method adopted for the calibration and subsequent readings of the disks. Once this loading and calibration procedure had been carried out the device was immediately located on the subject. The subject would then carry out their normal daily activities. In all the tests carried out on the photographic dose meter, the device was located on the subject's lapel. Once the recording run had been completed the disks were unloaded and developed in safe-light conditions using a Kodak safe-light filter, No.1 A (red light) covering a 25 watt pearl lamp and at a distance of at least 1.2m. Kodalith Super RT developer was used at 20 degrees C and development times were as

45


recommended, around 2.25 to 3.25 minutes. Once washed and dried the developed disks were mounted in 35mm clear glass projector slides and were loaded into a magazine and projected onto a matt black surface at a standard distance of 8 meters in a darkened room. To measure the density of the traces the disk was 'read' using a projector and light meter arrangement. A diagram of the projector and screen arrangement for reading the disks is shown below in Figure

2.4. MATT BLACK SURFACE

35 mm SLIDE PROJECfOR

wrm TI-IE DEGREED CIRCUMFIRENCE

DISPLAY ING IMAGE OF

INSCRIBED UPON IT

DlS K.

!

t

1.7Sm

+ ... ~1------- &.om ------1 ... •

Figure 2.4

Diagram of the projector and screen arrangement used to read the disks.

Inscribed on the matt black surface was a circumference divided into 360 degrees. The benchmark trace was located at 0 degrees and the ensuing traces were read off directly as functions of time. Therefore three and a half hours into the recording can be located at the position the hour hand would be on a conventional 12 hour clock face i.e 3:30. A light meter was placed at the projected benchmark position and a reading taken. This reading could be equated to the original lightmeter reading taken during the calibration procedure and the ratio between the two established. By incorporating this ratio into the linearity equation of the film the actual illumiance reading (in lux) was established. All subsequent readings from the 360 points on the circumference were converted to true lux readings using this equation. The reading circumference was located towards the outer edge of the disk to maximise the resolution of the readings and since the effective sample rate was approximately 2 minutes (the maximum readable resolution of the film) a histogram can be produced. An important point about the nature of the photographic light dose-meter is that the method of recording the light levels by letting light fall continuously on a constantly rotating photographic disk gives a wholly integrated measurement of the light levels. With the projector and light meter reading method used at the time, this particular advantage was nullified by taking what in effect where instantaneous samples at approximately 2 minute intervals. Were the system of reading the disks to be developed further, an integrating light meter would be fixed at the zero point of the circumference and

46


the image of the disk rotated between degree marks at a rate of one degree mark per 2 minutes. The integrated readings would be read every 2 minutes and the light-meter reset to read the next degree mark. This would ensure wholly integrated results.

2.1.5. Experimental trials using the dose meter A series of four validation trials were carried out on the photographic dose-meter towards the end of May 1989. Each trial or recording run was carried out on different (non-consecutive) days. In each case the primed dose-meter was placed in the lapel position on the researcher and left to run for a fixed length of time (between 2 and 9 hours). During that time the researcher took averaged light level readings over a two minute period at the position of the dose-meter every time there was a major change in the overall illuminance (for instance when moving from one room to another or from inside to outside) and recorded them against the time at which they occurred. This method was fairly crude but did allow correlations to made between obvious periods of high and low exposure on the disks and those perceived and recorded visually and quantitative ly at the time. Minor adjustments such as altering the thickness of the adhesive material for the disks, re-light proofing the casing (because of leaks) and narrowing the slit width to improve resolution were made between the recording sessions to improve the quality of the traces. From the disks, the light levels in tux were derived using the methods outlined above and graphs drawn comparing the readings from the disks and the readings taken with the light-meter. Although a direct correlation between the timing of changes in light levels measured with the light meter and the dose-meter was conclusively established, the correlation of the quantities for those levels was not. A typical comparative graph for one of the recording runs which illustrates this discrepancy is shown below in figure 2.5.

'.

10.M,

I

0

1

•;

'

'i

1..11. iI I

+ 1HOURS 1

I

I

s

'

1

·I

'

'I I.

'!

lI I

Figure 2.5 A Typical example of the comparative graphs of light levels measured with the lightmeter (L.M.) and the dose-meter (D.M.). Graph B - 21 May 1989.

47


The possible causes of the large inaccuracies in the measurement of magnitude of light level could be attributed to a number of causes any one of which could create substantial errors. Although the number of light level readings taken in the field compared to those taken from the disk were relatively few there were sufficient to be able to say with some certainty that the errors were unlikely to lie in the validation process. They possibly originated in the dose-meter itself but most likely

in the processes of calibrating and developing the disks. The development of the photographic dose meter was restricted, more or less to a feasibility study. There were aspects of the design where some inherent inaccuracies were unavoidable such as the difficulty of maintaining the high quality of chemical processing of the film that was required, the limited spectral sensitivity of the film and the possibility of non uniform rotation speed of the disk due to wear of the mechanical components. For these reasons it was not felt to be a device whose results (at that stage of its development) could wholly be relied upon for the degree of accuracy required. It was recognised that the nature of the research did not require a large scale survey of occupants to be actually carried out, only to establish beyond doubt, that with further development of the device such a survey would be feasible in the future. The results of the photographic light dose-meter have proven that this is possible and no further need was seen to carry on the development of the device. What was required was a completely accurate method of measuring light dose for small numbers of subjects rather than large numbers. This reduction in the numbers of subjects who would have to be surveyed simultaneously meant that a more elaborate (and expensive) electronic device could be considered. Having brought the experimentation with the photographic light dose-meter to a conclusion the work on the electronic dose-meter began in earnest in June 1989 when the principal components became available.

48


2.2. The electronic light dose meters

2.2.1. Summary In order to obtain accurate measurement of occupant light exposure within buildings, two electronic light dose meters have been devised and used to measure accurately the light exposure of occupants in buildings.

2.2.2. Description of the electronic light dose meter An electronic 'Squirrel 1202' data meter/logger manufactured by Grant Instruments (Cambridge) was purchased as the basis of the electronic light dose meter. It was designed by the manufacturers to record temperature from 8 thermistor probes, voltage/current at 8 inputs, and pulse rate or pulse count from 2 inputs. It had no facility to measure light levels directly. For its 18 inputs, it would record average or instantaneous readings at a predetermined sampling rate (1 second to 24 hours) and record the readings in its 42 Kbyte solid state memory. These data could then be downloaded to a PC at the end of the recording period into Lotus 123 format spreadsheet for analysis. A photograph of the logger is shown below in Figure 2.6.

Figure 2.6

The Grant 1202 'Squirrel' meter/data logger. (Courtesy of Grant Instruments).

To use this particular data logger (which was selected mainly because it was small enough to be worn by a subject) for measuring light levels, it was necessary to first build photometric sensors which would give a suitable input to the logger, which although they wou ld give a readout in degrees centigrade, volts or amps could then be calibrated against a light meter and an equation derived to convert the logger readings into lux readings. Two options for photometric sensors were considered, photo-voltaic and photo resistive, both of whose outputs could be recorded by the logger. In the event the availability of cadmium sulphide photoresistive cells with a spectral sensitivity that corresponded closely to the CIE

49


Standard Photopic Observer curve (no such voltaic cell could be found at reasonable cost), decided the issue. Two cosine corrected photometric sensors were then manufactured from Cadmium Sulphide photo-resistive cells and incorporated into suitable aluminium casings to give 180 degree angles of view. The spectral sensitivity of the cadmium sulphide photocells is shown below in figure 2.7 compared with the standard CIE Standard Photopic and Scotopic

curves. Figure 2.8 shows a diagram of the completed photometric sensors.

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Preliminary trials were carried out on where to place the sensor on the subject. Given the visually mediated phenomena under cons ideration the most successful option tried was a simple elasticated headband on which was mounted a single forward facing photometric sensor with a 180 degree angle of view. The headband proved easy to put on, comfortable to wear for the length of a working day and It did not restrict the vision of the subject.

50


2.2.3. Calibration of the electronic light dose meter The sensor was calibrated by a having a projector set up at one end of a darkened room with its beam directed to fall on the opposite wall (about 8 meters away) at waist level. The sensor for calibration was connected to one of the resistive inputs of the data-logger and taped onto a light meter. The combination was held at the most distant point from the projector in the centre of the beam. A reading from both the light-meter (in lux) and the data-logger (in degrees centigrade) was taken and recorded in tabular form. The position of the combination was advanced towards the projector by about 300mm and another set of readings taken. This process was repeated 53 times to give correlated readings for the sensor (in degrees centigrade) from 125 lux - 6625 lux. The tabulated readings were graphed and typical results are shown in figure 2.9 below. 80

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The exponential equations which described the linearity of both photometric sensors were derived from the calibration data and they were used in all subsequent dose-meter monitoring exercises to convert the degrees centigrade reading of the data logger into Lux. This was carried out by applying the appropriate exponential equation to the degrees centigrade readings in a spreadsheet on a PC. It should be mentioned that this apparently simple stage of the operation took an unfortunately long period of time to systematise. The hardware and software available to the researcher were found to be incompatible for the task in hand and a lengthy process of conversion from one application to another had to be undertaken. After some time it became possible to transfer the

51


logged data directly to Microsoft Excel on the Macintosh for analysis and this is the process now used.

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The electronic light dose meter takes instantaneous readings at fixed sampling rates and stores these directly in memory or averages series of them and stores the results. This introduces what could be significant errors into the logged readings because they are not time step integrated. This was not the case with the photographic light dose-meter because it in effect took a continuous cumulative sample. To correct this, a future improvement to the electronic dose meter would be a time step integrator circuit which would integrate the output from the photometric sensor and deliver the integrated reading on demand to the logger. Within the confines of a limited research budget it was not possible to produce such a circuit so all data gathered using the equipment was necessarily discretised. SENSOll A (UJlO HI

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Figure 3.20 The BAS Simplified Daylight Table. The table gives sky components from an overcast sky for rooms with vertical rectangular windows glazed with clean, c lear glass. Allowance could be made for simple external obstructions, the use of other types of glass and the presence of dirt on the glass.

Figure 3.21 The Use of the BRS Simplified Daylight Table requires five dimensions of the room under consideration to be known in order to determine the sky component for a particular point in the room. H, the effective height of the window head above the working plane. Hw, the height of the working plane. W1 & W2, the effective widths of the window on each side of a line drawn from the view point normal to the plane of the window. D, the distance from the view point to the plane of the window.

Tables produced by the National Physics Laboratory (N.P.L.) in 1944 and 1949 and by Rivero in 1958 also produced results as sky components that were essentially the representations of the same geometrical relationships contained in the Waldram Diagram. The N.P.L. tables related the height of the window head above the working plane to the width of the window for various sky components. Its results gave the maximum distance of the reference point (view point) from the window at which the given daylight level was attained, the maximum breadth of contour of equal daylight level of this value and the area enclosed by the contour, that is the area of the room within which the daylight level is equal to or greater than the given amount. Rivero's tables gave both the individual contribution of small daylighting elements, and also the summation for vertical rectangular 112

3. Modelling light exposure

windows and horizontal roof lights as sky factors and sky components on vertical reference planes parallel and perpendicular to the window wall. Rivero's tables were based on three equations, one for sky factor on a horizontal plane, one for sky factor on a vertical plane parallel to a window and one for sky factor on a vertical plane at right angles to a window. A more widely used window angle model was the Building Research Station (B.R.S.) Simplified Daylight Tables. The B.R.S. Simplified Daylight Tables did essentially the same thing as Rivero's tables. They gave the daylight level on a horizontal plane in the form of a sky component both for a uniform sky and for a C.l.E. standard overcast sky at reference points at different distances from a vertical window, in terms of height Hand width W of the window and of the distance D to the view point. However Hopkinson states that; "the tables are not based on the formulae used by Rivero for his computations, but were derived from summated values of sky component.. ..... obtained graphically from a large scale Waldram diagram." No mention is made by Hopkinson of the degree of correlation between the two models.

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Figure 3.22 The BAE Daylight Protractors were a widely used method of determining sky components. They are quicker to use than grid methods (like the Waldram diagram) but are not as accurate for external obstructions of complicated outline. They were available for calculations with uniform or standard CIE skies, and various slopes of glazing. Transmission of single pane clear glass was allowed for.

A further development in daylight prediction and modelling was a later window angle nomogram that was developed at the Building Research Station by A.F. Dutton in 1946. It was called the daylight protractor. It was used to calculate sky components as percentages of the total area of the sky vault by laying a number

113


of transparent protractors directly on the plans and sections of the building (figure 3.22). This had the advantage that the sky component could be read directly from the protractor. The improvements in interior daylighting had thus far no direct basis in law and were only indirectly encouraged through legislation dealing with other aspects of environmental health. It was not until the rebuilding of the British cities after their destruction in the second world war, that an effort was made to establish a legal statute for daylighting in buildings. The 1959 Rights of Light Act leant heavily upon the Prescription Act of 1832 in determining how long certain daylighting benefits (principally sky factor) must have been enjoyed before they became established easements. An essential adjunct to the 'window angle' part of a model was the sky luminance distribution model. In order to derive illuminance levels within a room rather than just sky factors or daylight factors, it is necessary to know the luminous intensity of the visible patch of sky. Hopkinson stated that two basic forms of sky luminance distribution for calculation of daylighting in buildings could be considered; "(1) The completely overcast sky, which may either be considered as of uniform illuminance, or which may have a given non-uniform luminance distribution .... (2) The clear blue sky with sunlight, for which a luminance distribution for the sky may be obtained from a knowledge of the sun's position ... the relevant scattering constants of the atmosphere ...... [and] the reflecting properties of these [ground and vertical] surfaces." N

Figure 3.23a. The luminance distribution of a clear blue sky measured at Stockholm on October 2nd 1953 at 14.25 - 14.50 solar time. The position of the sun is indicated by arrows. From Hopkinson 1966.

Figure 3.23b. The luminance distribution of a fully overcast sky measured at Stockholm on October 10th 1953 at 09.55- 10.15 solar time. No individual clouds or bright patches were visible. From Hopkinson 1966.

However, common experience is that in the UK real sky conditions are rarely either of these two meteorological extremes. To have a perfectly overcast sky fo r 114


instance the sun must be totally obscured, by cloud, dust or mist. The sky luminance changes predictably with the diurnal and seasonal variations in sun path but more importantly it varies unpredictably with weather conditions. A number of models have been developed of varying complexity and representational accuracy to describe the luminance of skies. However for a north European maritime location the model most often considered has been of cloudy sky conditions since this is the most prevalent meteorological state of the sky there. In all situations where a perfectly overcast sky is not the case then the sun will make a significant contribution of direct solar radiation to the viewpoint as well as the diffuse component from the rest of the sky vault.

Figure 3.24 The Building Research Establishment Sunlight Availability Protractor. The protractor is used to determine the solar azimuth and altitude at a particular time on the 21st of each month for locations at latitude 51.5 degrees N.

Prior to 1942 it was customary to base sky luminance calculations on the assumption that an overcast cloudy sky was of uniform illuminance. The advantages of this assumption are chiefly mathematical but the resulting simplifications in calculation were offset by non-trivial errors when considering the design of wholly side lit interiors. Until quite recently in the United States, models of clear and overcast skies were based on the work of Kimball and Hand at the U.S. weather Bureau from 1919 to 1922 19. The authors point out that their measurements and data varied between 60 and 150% of the average for clear skies; and for cloudy skies between 30 and 200%. Their model has been found to be in error at the larger solar altitudes 20. It was recognised that improvements in the realism of sky luminance distribution models were required. Hopkinson describes a fully overcast sky model developed by Moon and Spencer 1a where the sky is brightest at its azimuth and the luminance decreases systematically until at the horizon it has only one third of the zenith value. With such a sky model, the luminance at any point of the same

115


elevation above the horizon was the same , irrespective of the altitude of the sun or the orientation of the observer. However this model did not account for reflection properties of the ground and of course represented a rarely occurring sky condition. In order to give more precision to the modelling of daylighting in buildings the International Commission on Illumination (the C.l.E.) in 1955 adopted as standard

a distribution of relative sky luminance in accord with the luminance distribution of the overcast sky as obtained from measurements in different parts of the world. The C.l.E. confirmed Moon and Spencer's formula with the measured data and subsequently defined the C.l.E. Overcast Sky by the formula; Btheta=Bz* (1 +2 sin theta)/3 Where Btheta=Luminance at the sky point, Bz=the luminance of the sky at the zenith and Theta= the altitude of the sun. The C.l.E sky allows for a variation in sky luminance dependent on altitude of the sun and an assumed sky brightness at the zenith. It is omnidirectional and does not allow for the azimuthal variation in the sun's position. This has serious deficiencies when the directional aspect of solar illuminance is important. The C.l.E. sky also represents a worst case situation and not 'average conditions' as is sometimes erroneously assumed. In reality illuminances are often much higher than the C.l.E. sky predicts so for instance, a south facing window designed using this sky may cause excessive illuminance and overheating. Recently, interest has arisen in providing data for a third sky condition, the partly cloudy sky. It has been the practical difficulty of making instantaneous detailed sky luminance distribution measurements over long periods that has prevented a more accurate model of the variations in cloudy sky luminance distribution being developed. However data was collected by Wegner in Berlin in 1974 (Wegner, J. 1975) which was used in 1982 by Littlefair, Crisp and Lynes at the Building Research Establishment, Garston UK, to develop the BAE Average Sky model. For particular solar altitudes this gives the luminance of an 'average sky' which represents the average of a succession of real skies incorporating a whole range of weather conditions. This has the advantage of being able to predict the effects on interior daylight of orientation of windows, sunlight in buildings and time of day and year. Surface reflection models have been a relatively recent addition to the indoor illuminance model. Their purpose is to simulate the contribution of daylight reflected from internal and external surfaces to the illuminance at a viewpoint.

116


They consist of two parts, externally reflected component (ERC) and the internally reflected component (IRC). Daylight may reach a point on a horizontal plane within a room in three ways (figure 26), from the sky component as already discussed, from the ERC and from the IRC. The total illuminance at the point is the sum of these three components. \

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Figure 3.25 The three ways in which daylight may reach a point on a horizontal plane within a room. A= sky component, B =externally reflected component and C= internally reflected component. Note the IRC includes external to internal reflections. 20.

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Figure 3.26 Diagram of the split flux principle applied to the calculation of the internally reflected component (IRC). C1 and C2 are functions of the flux entering the room from above and below the horizontal respectively, Rfw and Rew are the average reflectance's of the lower and the upper parts of the room which receive light directly from the sky and from the ground respectively 20.

The ERC is the fraction of illuminance at a view point that is received directly from

externally reflecting surfaces such as walls and the ground. The contribution of direct sunlight is excluded so that the ERC considers only the diffuse component from the sky. It is customary to assume an average luminance for all such external obstructions expressed as a fraction of the average luminance of the sky as a whole (often 1/10th) and in the case of the CIE sky for obstructions near the

117


horizon 1/Sth of Hz, the luminance at the horizon. It is generally assumed that the externally reflected component is of relatively minor significance to the overall illuminance at a point within a building. Hopkinson states; '..... the externally reflected component is very rarely more than a small fraction of the total daylight illumination which reaches the reference point. Excessive concern with accuracy is therefore misplaced in its calculation. 'Hopkinson 1966 p.72 The IRC is the fraction of illuminance at a view point that is received directly from internal reflecting surfaces such as walls and the floor and again the contribution of direct sunlight is excluded. The most common model of the internally reflected component is the B.R.S. Split Flux model which is based on the theory of the integrating sphere. It divides the flux entering a room through an aperture into two parts, first, that entering the room directly from the sky or from obstructions above the horizon, and second, flux which enters the room directly from the ground, that is, skylight reflected from the ground. The upper flux entering the room is considered to be modified by the average reflectance of the surfaces of the room as seen from the sky, and the ground component to be modified by the average reflectance of the surfaces as seen from the ground (figure 3.26). A less common but perhaps more accurate model of internal reflection is ray- tracing. A ray of sunlight entering a room is given vector dimensions and the surfaces of the room given absorption and reflection characteristics. The inter-reflection of the vector between surfaces is calculated and the magnitude at each surface recorded until absorption has reduced the magnitude of the vector to a threshold level at which point calculation ceases. This process is carried out for incident rays of sunlight of various directions and the intensities on points on the surface plotted. A further refinement of this process is backward ray-tracing whereby a point on a surface within the room is established and the vectors of inter-reflection traced back to a grid of points on the window. This necessitates fewer iterations of the calculation in order to establish the illuminance at a specified point. The ray-tracing method of internal reflection calculation is commonly used in rendering programs for three dimensional computer models where a high degree of accuracy is required to achieve a visually realistic scene. Its cardinal disadvantage is that it is a computationally intensive technique unsuitable tor manual use and often requiring

many hours of computer time. Whilst the three major components of modern daylighting models can be used "manually" in paper and pencil based calcu lations, they are more commonly embodied in the form of algorithms programmed in computers. Currently there are

118


many such computer models in existence, however most of them are based on combinations of the calculation methods described above. Computer based daylighting models tend to be used exclusively for either calculating illuminances on working planes in interiors or for producing visualisations of interiors. As far as can be determined, no computer based daylighting models have been built in the past specifically to examine the health and well-being of building occupants.

11 9


3.3 The GOLD Model 3.3.1. Summary In order to predict the effect of proposed building designs upon the circadian phase shifts that may be expected within building occupants a model has been produced and coded in 'C' for Macintosh ® computers. The GOLD model (Guide to Occupant Light Dose) consists of two parts, a daylighting and occupant location integrator and a circadian phase shifting model. From input data on the geometry, glazing and surroundings of a building and the location and behaviour of the occupants within the building, light exposure histograms can be produced showing the variation in light exposure that an individual would experience over the course of a working day and from these data the probable shift in circadian phase is derived. 3.3.2. GOLD as a research tool The GOLD model is intended to be primarily a research tool for examining the interrelationships of natural daylighting, building design, occupant behaviour and occupant circadian phase from which generally applicable design guidelines may be derived for the benefit of building professionals. As such it is one of a new genre of "behavioural" models that focus on the interaction of the occupant with their environment. Three main issues were addressed during the conceptual development of the model as a research tool: 1)

The model should not be over-simplified, particularly in its

representation of daylighting in buildings. The problems inherent in oversimplification have already been touched on and it was recognised that in this particular case it was probable that over-simplification of the analytical model would be unlikely to yield realistically useful results. 2)

As far as possible the model should be based on already validated

algorithms and empirical data. It was not intended to focus the research on a lengthy exercise in the methodology of validation of new algorithms, but rather to use the best of those algorithms and empirical data already available to establish a framework for the analysis. It was intended that this approach would not only identify those algorithms that could most usefully be improved in future but more importantly it would allow in-depth analysis of building designs rather than computer code.

120


3)

The model should maximise its computational speed within certain

limitations. The nature of the algorithms available for developing a model of suitable accuracy for daylighting and circadian rhythmicity involve many functions that are highly iterative. Large and useful increases in accuracy, particularly for numerical integration can be gained by decreasing the increments of integration and increasing the number of cycles. This had to be balanced against the need for the final model to be implemented at modest cost on a desktop computer.

3.3.3. GOLD as a practical design tool Subsidiary to the main role of GOLD as a research tool was the possibility that it might eventually form the basis of a software application to be used interactively during the building design process. This necessarily implied that a non-expert might have to use GOLD. This limitation to wider acceptability was realised before development began, therefore GOLD was developed as a computational kernel about which could be wrapped a user interface. A prototype user interface was developed and is briefly described later. The user interface was seen as a side issue of the main research objective and although of interest in its own right was developed as a two month pilot study indicating a path for future development rather than a definitive solution. A 'cut down' version of GOLD (without the user interface) is in use for research purposes but it requires considerable expert knowledge to be able to use. To achieve a computational speed that allows realistic research times, a concise programming language was required and a powerful desktop computer. Unfortunately neither of these resources was available to the author in the first instance. In 1991 the author purchased a Macintosh LC computer and Microsoft Quick Basic programming software and developed the GOLD model with them. Computation time for a simple room with one window was approximately 45 minutes, too long for detailed building analysis. In 1993 the author acquired a more powerful Macintosh Quadra 800 20/240 which cut the computation time for the same room and window to 7 minutes, this cut analysis times by a factor of six. The Model was re-written in C, with enhancements to the logic of the code structure which reduced the computation time for the same task to 35 seconds. This is the final form that the GOLD model now exists in and is the one used for all the analytical work described in this thesis. The Macintosh platform was chosen because it offered the opportunity for developing a high quality user interface and is a computer widely used within the architecture profession. What follows is a detailed description of the GOLD model in terms of the algorithms it uses and the code structure in which they are assembled.

121


3.3.4. The sky luminance distribution algorithm

A prerequisite to assessing the probable circadian phase shift that would be induced in occupants by a building is an ability to calculate daylighting levels in all parts of the building at any date and at any time of day. Most existing daylighting models in common use involve the use of daylight factors together with a CIE overcast sky to predict internal illuminance 1. The value of unobstructed horizontal illuminance outdoors is normally chosen to be 5000 Lux and this, multiplied by the daylight factor, gives the internal illuminance which is then compared with a recommended level 2. This approach, however, obviously has its drawbacks. The CIE standard overcast sky represents a particular type of 'worst-case' weather condition, and the 5000 Lux level outdoors is exceeded 86% of the time during a 09:00 - 17:00 working day 3. Windows, atria and other glazed areas designed using the CIE model of the sky will almost always admit enough daylight during normal working hours; but this is an 'all-or-nothing' approach which is incompatible with any requirement of the designer to minimise energy consumption by balancing the energy savings made by using daylighting to offset artificial lighting loads with energy losses due to increased glazing area. It also does not take account of glare, thermal comfort, and requirements to maintain the comfort and health of building occupants. The view out and external appearance are also ignored. The CIE model of sky luminance is simply not suited to integrated design. A possible approach to overcome this problem is to use the CIE daylight factors together with horizontal illuminance data to predict daylight availability indoors throughout the year 4 . However, Tregenza s has shown that this method is inaccurate. He found that the ratio of internal to external illuminance often varied by factors of two or three. Daylight availability indoors depends not only on the horizontal illuminance outside, but also on the luminance distribution of the sky. For example, the CIE model or its modification above cannot predict effects due to the orientation of windows or other glazed areas because the CIE model of sky luminance distribution does not vary with azimuth. The resulting errors in predicted indoor illuminance can be large in practice. Such changes in the orientation of windows and glazed spaces in buildings are crucial to the accurate prediction of the timing of occupant illuminance and subsequent circadian phase shitting of building occupants. In 1982 the previously mentioned BAE average sky method of representing sky luminance distribution was developed 6, 7, s. For a particular solar altitude, this gives the luminance distribution of an 'average sky' which represents the average over a succession (typically several years) of real skies incorporating a whole range of weather conditions. This has the advantage of being able to predict the effects on interior daylighting levels of orientation of windows, sunlight in buildings and time of year and day. The BAE average sky model used in GOLD

122


has been taken from a paper presented at the CIBS National Lighting Conference, Warwick University in 1982 by P. Littlefair 9. This gives a mathematical description of the average sky luminance, drawing on data gathered over several years observation of real skies at Berlin and incorporating a full range of weather conditions. The data was for Berlin, and since detailed data on sky luminance for British weather conditions are not available, Littlefair adjusted the constants in the Berlin model to fit horizontal illuminance data collected by the meteorological

office at Kew, assuming that the form of the sky luminance is the same in Berlin and Kew and that only the magnitudes differ. The difference between Kew and Berlin is not great, varying between plus and minus 15% as sun height varies from 10 to 60 degrees. The model may therefore be used with some confidence throughout southern England and with the substitution of the Berlin data, for Europe at similar latitudes. This paper also gives an expression for calculating illuminance due to the direct sun and a method for calculating an average value for the illuminance due to reflection from the internal surfaces of the room, the so called internally reflected component or 'IRC'. It also provides formulae for calculating the outdoor illuminance due to diffuse sky on vertical and horizontal surfaces. The diffuse luminance of the sky vault is given by: L=a(h5 ) exp(-0.025y) + c(h 5 )

kcdfm2

(1)

where 'a' and 'c' are functions of sun height (hs) in degrees and 'y' is the angular distance in degrees from the sun to the point in the sky vault under consideration. The sky luminance 'L' is the illuminance in kilolux on a plane normal to the element of sky being considered per unit solid angle of sky. The uniform component 'c' is given by C=0.22+0. 1032*h 5 -0.000394*(h5 )2

(2)

The pre-exponential factor in the circumsolar component, 'a' is given by a=0.37+0.076*{h5 ) 1.8 *exp(-h 5 /32)

(3)

The value of 'L' is shown graphically against the angular distance 'y' for four

values of sun height in figure 3.27.

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To use this model of the sky, GOLD calculates values for the solar altitude and azimuth from the position of the sun relative to the earth's surface in terms of declination and local hour angle. Declination, the angular distance (in degrees) of the sun from the equator with North indicated by a positive val ue and South by a negative is given by:Dec=23.45 sin b

(4)

Where b is the angle of orbital rotation given by:b= (Dn-81)/365 (5) Dn is the number of days since the start of the year. The local hour angle is the angle between the sun's meridian and the local meridian. It is given by :H la=(li-720)/4

(6)

Where It the local time in minutes is given by:l1=C1+e1+4*(1tz-lg1)+d (7) Where ct is clock time, ltz is the local time zone in degrees, lgt is longitude, d is a correction for British Summer Time applied between 24th March and 27th October. The equation of time (et) , is the correction to clock time for the changes in day length due to the earth's elliptical orbit. It is given by :-

124


et=9.87*sin(2b)-7.53*cos(b)-1.5*sin(b)

(8)

The sun's height and azimuth m ay now be calculated using the formulae of spherical trigonometry as illustrated in figure 3.28.

Declination

Lattitude

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(9) (10)

Figure 3.28 The sun's height and azimuth calculated using the formulae of spherical trigonometry.

The azimuth angle thus determined is always positive and requires to be set to the same sign as the local hour angle . Given values for the angular height 'h' and azimuth, of the element of sky under consideration, the value of 'y' may now be calculated using the cosine formula of spherical trigonometry as illustrated in figure 3.29 Zenith

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(11)

Figure 3.29 The value of 'y' calculated using a formula of spherical trigonometry

125


Where

a, the horizontal angle between the sun and the element of sky is the

difference between the two azimuths.

3.3.5. The window angle algorithm Calcu lation of the level of illuminance at a particular point in a room due to sky luminance requires the summation of the contributions of all the elements of sky visible at that point through the various windows, a calculation most conveniently performed using numerical integration. As an aid to verification of the code used in GOLD two different methods of integration were tried for both windows and roof lights. The first, a two dimensional version of Simpson's rule 10 was used for both windows and roof lights. Simpson's rule has the advantage, apart from mathematical respectability, that the required accuracy can be pre-set and ordinates added till the required accuracy is achieved. It is, however, slow. At least nine function evaluations are required for even the smallest area. The code finally adopted used different methods for windows and roof lights. The method used for windows simply divided the window area into small rectangular solid angles and used the brightness at the centre as an estimate of the average over the whole area. This was found to give adequate accuracy by compa rison with Simpson's rule if a ten degree square area of sky was used as the unit of integration. It was also faster. Horizontal Narrow Strip Upper Window Angle

Point o f - ~~~_.__._....___.__,I Observation Vertical Narrow Strip

Figure 3.30 Method of numerical integration using ten degree square areas of sky as the units of integration.

The method of integration is illustrated in figure 3.30. Starting at the left hand edge, the window area is divided into vertical strips each subtending a horizontal angle of 10 degrees at the point of observation together with a narrower strip at 126

3. M odelling light exposure

the right hand edge. The vertical angles of the upper and lower edges of the centre of the first strip are then calculated and this strip divided into 10 degree high blocks starting at the bottom end leaving a narrower block at the top. Multiplication of the solid angle of each block by the brightness at its centre followed by correction for absorption in the window glass, gives an estimate of the illuminance at the point of observation. The remaining vertical strips are treated in the same way and the results added, a correction being made for the narrower blocks at the end of each strip and the narrower strip at the right hand edge of the window. Each value is multiplied by the sine of the vertical angle to convert from direct illuminance to illuminance on a horizontal plane. The algorithm is coded by summing the contributions of the blocks in a nested double loop. If an overhang is visible through the window then this, rather than the upper edge of the window marks the upper limit for summation.

3.3.6. The external obstructions algorithm Obstructions are assumed to be parallel to the window, of infinite length and to have a horizontal upper edge. If an obstruction is visible through a window two summations are made, using the sky luminance for areas above the obstruction and the luminance of the obstruction for the lower area. The obstruction luminance is the illuminance impinging on the obstruction due to both sky and direct sun, multiplied by its reflectivity and divided by 7t. A completely accurate calculation of the obstruction luminance would involve a consideration of the shadow of the building on the obstruction and the shielding of part of the sky by the building, together with additional luminance due to reflection from the face of the building and from the ground. In view of the relatively small contribution that these refinements were expected to make to the total illuminance within the room, in cases that it was intended to consider, i.e. obstructions at some distance from the building, it was thought that the resultant complexity of the code was not justified, and the following simplified scheme was adopted. If the building casts a shadow at any point on the wall within the width of the building the effect of direct sun is ignored. The shielding of part of the sky by the building is ignored, as is the reflection from the building and the ground. The underside of the overhang is il luminated only by reflected light from the ground, the obstruction and the building fa9ade. The luminance is therefore expected to be small, and any contribution from this source has been ignored.

127


Direct Solar Component

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155

4. Validation of the GOLD model

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A further comparison with the base case room was made for a similar room configuration but one where all four walls and the roof were completely glazed, in

163

5. Parametric studies using the GOLD model

effect a glass box. This was to indicate an upper limit to the +ve circadian phase shifting under daylighting conditions as close as possible to those occurring outdoors. As can be seen from figure 5.5, the general trend of circadian phase shifting in close to outdoor daylighting conditions is again one of increase from January to June, however the aberration due to the transition from daylight saving time to British summer time is less marked in relation to the general trend than in figure 5.3. It will be noted that the effect of imposition of daylight saving time is to increase the magnitude of +ve (and it is assumed beneficial) circadian phase shifting in the winter months. The magnitude of variation in the "glass box' is substantially higher than in the base case room, as one might expect where overall illuminance levels are greater.

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