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Daylighting in atrium spaces Iyer, Usha 1990

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c D A Y L I G H T I N G IN A T R I U M S P A C E S by U S H A IYER B . A r c h . , U n i v e r s i t y of B o m b a y , India,  1988  A THESIS SUBMITTED IN PARTIAL F U L F I L L M E N T O F THE REQUIREMENTS FOR T H E DEGREE OF M A S T E R IN A R C H I T E C T U R E  in  T H E F A C U L T Y OF G R A D U A T E STUDIES (School of Architecture)  W e accept this thesis as conforming to the required standard  T H E UNIVERSITY O F BRITISH October ©Ushalyer,  1990 1990  COLUMBIA  In  presenting  degree  this thesis  in partial fulfilment of  requirements  for  an  of this thesis for scholarly  department  or  by  his  or  her  I further agree that permission for  purposes  may be granted  representatives.  It  is  permission.  Department of  ArmH-fec-j'Ug-g'  The University of British Columbia Vancouver, Canada  extensive  by the head of  understood  that  publication of this thesis for financial gain shall not be allowed without  DE-6 (2/88)  advanced  at the University of British Columbia, I agree that the Library shall make it  freely available for reference and study. copying  the  copying  my or  my written  11  ABSTRACT  A m o n g the  different environmental functions atria  focused only on daylighting.  perform, this research  T h e thesis has been presented in two parts.  has  T h e first part  provides the background information, the extent of daylighting research in atria, objective and scope of the research.  T h e environmental role of atria has also been discussed.  The  second part deals with the research procedure, the description of the scale model used for the study, the conditions under which the study have been conducted, and finally,  the  conclusions of the study. T h e effects of changing the reflectivity of the wall and floor surfaces of the  atria  well on the illumination in the adjacent spaces to atria have been studied. T h e objective of the  thesis  was  to  establish  the  relative  contributions  of the  changes in the  surface  reflectance of the wall a n d the effects of variations in the area of the openings in the wall facade on lighting in the adjacent occupied spaces.  T h e importance of the floor reflectivity  in lighting the spaces adjacent to the atria was also determined. Quantitative analysis of daylighting in atria has been conducted using physical scale models under n a t u r a l overcast skies u s i n g daylight factor and well index to normalize the results. A l t h o u g h the thesis has concentrated  on daylighting, in reality there are  other  functions, both social and environmental, that atria are required to perform, a n d where appropriate, these functions have been acknowledged. It has been established b y this research, that the atria well and the spaces adjacent to it are affected by changes in the a r e a of openings in the form of windows in the wall facades of the well.  S m a l l variations in higher reflective surfaces on the wall facade  iii  produce greater differences in the daylight factors as compared to similar differences in surfaces with lower reflectances. Using  high  surface  reflectance  on  illumination in the lower levels of the atria.  the  floor  of the  atria  well  will  enhance  A s the a r e a of the (high) reflective  surfaces  along the edges of the floor is increased, the illumination in the side spaces in the lower levels also increases.  T h e area of floor reflectivity needed for increasing the illumination  levels in the side spaces is dependent on the area of openings on the walls at the lower levels.  iv  TABLE OF CONTENTS  Abstract  ii  Table of contents  iv  List of Figures  viii  List of Graphs  ix  List of Plates  x  Acknowledgement  xi  Introduction  1  PART 1  Chapter One: Daylighting in atria 1.0 Daylighting research  4 4  1.1 Physiological, psychological and aesthetic benefits of of daylight  4  1.2 Daylighting research for energy savings  6  1.3 Daylighting strategies in atrium buildings  7  1.3.1 Traditional techniques  7  1.3.2 Reflective techniques  8  2.0 Lighting in atria  10  2.1 Atrium well  10  2.2 The spaces adjacent to atrium  11  3.0 Objective  11  4.0 Scope  12  V  Chapter Two: Environmental role of atria 1.0  2.0  Non-energy related phenomena  14 14  1.1  Fire protection  14  1.2  Acoustics  20  1.2.1  Reflection  21  1.2.2  Absorption  21  1.2.3  Transmission  22  1.2.4  Shape and volume  23  E n e r g y related phenomena  24  2.1  H e a t i n g and ventilating  25  2.2  Lighting  26  2.2.1  Sunlight  28  2.2.2  Daylight  29  3.0  L i g h t Wells  29  4.0  Design of atria  32  5.0  P h y s i c a l characteristics of atria  35  5.1  Proportions  37  6.0  W e l l Index  38  7.0  Bounding elements  38  7.1  Roof 7.1.1  7.2  7.3  42 G l a z i n g materials, form and shape  Walls  42 43  7.2.1  W a l l reflectivity  43  7.2.2  F a c a d e arrangements  47  A t r i u m floor  47  VI  PART 2  50  Chapter Three: Methodology 1.0  Model studies 1.1  1.2  50  Models for practice and daylighting research  51  1.1.1  Quantitative studies  52  1.1.2  Qualitative studies  53  Model used for the daylighting study  53  1.2.1  Model design and construction  53  1.2.2  Materials  56  1.2.2.1  Reflectivities  1.2.2.2 L i g h t  56  tight  57  1.2.3  Size and scale  58  1.2.4  Measurements  60  1.2.5  M e a s u r e m e n t process  62  1.2.5.1  Walls  62  1.2.5.2 Floor  65  2.0  Daylight Factor  66  3.0  S k y condition  67  4.0  Location  70  71  Chapter Four: Results 1.0  D a t a analysis  71  1.1  Walls  71  1.2  Floor  77  1.2.1  Entire  1.2.2  Specific parts of  floor  79 floor  88  vii  1.3 2.0  W e l l index  D e s i g n implications 2.1  Discussion  93 93 102  Conclusion  105  References  110  Appendix A  120  Appendix B  122  viii  LIST OF FIGURES  Figure 1  L i g h t i n g in atria  9  Figure 2  Smoke extraction v i a a t r i u m space  17  Figure 3  Sound in atria  19  Figure 4  N a t u r a l lighting in atria  27  Figure 5  L i g h t well and a t r i u m  30  Figure 6  A t r i a design to support natural lighting  31  Figure 7  Different techniques for admitting light into atria  33  Figure 8  Generic forms of atria  34  Figure 9  A t r i a proportions in p l a n and section  36  Figure 10  Selection of roof glazing affects lighting in atria  39  Figure 11  Different types of roof forms  40  Figure 12  Roof orientation for t h e r m a l benefits  41  Figure 13  V a r i a b l e openings on atria facade to acknowledge the differences in daylight levels  45  Figure 14  F a c a d e arrangements to promote n a t u r a l lighting  46  Figure 15  Atrium  48  Figure 16  D e s i g n of model a t r i u m  54  Figure 17  Different arrangements of photo cells  59  Figure 18  Positions of photo cells i n the model atria  61  Figure 19  M e a s u r e m e n t s at lower well indexes  63  Figure 20  Effects on light distribution b y v a r y i n g reflectivity of  floor  perimeter of floor  Figure 21  Stable sky conditions for daylighting analysis  64 68  ix  LIST OF GRAPHS  Graph 1  V a r i a t i o n in daylight factors for 25% opening  72  Graph 2  V a r i a t i o n in daylight factors for 50% opening  73  Graph 3  V a r i a t i o n in daylight factors for 75% opening  74  Graph 4  D a y l i g h t factor and wall reflectivity at 3.0m and at well index 1.95  Graph 5  78  D a y l i g h t factor and wall reflectivity at 3.0m and at well index 0.375  80  Graph 6  D a y l i g h t factor and wall reflectivity for 25% openings at 3.0m  82  Graph 7  D a y l i g h t factor and wall reflectivity for 50% openings at 3.0m  83  Graph 8  D a y l i g h t factor and wall reflectivity for 75% openings at 3.0m  84  Graph 9  F o r various openings using white floor at 3.0m  86  Graph 10  F o r various openings using black floor at 3.0m  87  Graph 11  D a y l i g h t factors for specific parts of the floor (along perimeter)  89  Graph 12  D a y l i g h t factor and well index at 3.0m  92  Graph 13  V a r i a t i o n in illumination using 90% floor reflectivity  95  Graph 14  V a r i a t i o n in illumination using 5% floor reflectivity  96  Graph 15  V a r i a t i o n in illumination at different levels for well index 1.95  98  Graph 16  V a r i a t i o n in illumination for changes in reflectivity along perimeter of  Graph 17  Illumination and well index at 3.0m  floor  99 101  LIST OF PLATES  Plate 1  A t r i u m spaces in shopping malls  72  Plate 2  A t r i u m spaces i n office buildings  73  Plate 3  A t r i u m well i n model  74  Plate 4  Office space i n model a t r i u m  78  Plate 5  Photo cells in model office room  80  Plate 6  M e g a t r o n light meter  80  Plate 7  A t r i a walls lined with 75% opening size  80  Plate 8  M e a s u r e m e n t s at well index 0.375  80  Plate 9  Location of model  80  xi  ACKNOWLEDGEMENT  I wish to express m y sincere gratitude to m y thesis advisor, D r . R a y m o n d Cole for his invaluable guidance throughout the course of this study. I also w i s h to acknowledge m y f a m i l y and m y friends for their continuous m o r a l support d u r i n g m y stay here.  1  INTRODUCTION  A review of a t r i u m buildings in the past decade suggest that the design of atria as a n architectural feature was conceived m a i n l y for their aesthetic and commercial values. A t r i a have been used extensively in different types of new structures to offer user amenities and social interaction in a tempered environment.  N o t only do atria provide  physical a n d visual cohesiveness to the entire structure, they also provide environmental benefits.  T h e environmental potential of the atria is still to be consciously explored.  A t r i a originated in the R o m a n times as the physical and social center of the house, with  the  intention  of  providing light  and  ventilation  to  C o n t e m p o r a r j ' atria are not necessarily in the geometric  the  spaces  surrounding it.  center of the structure,  but as  given by Bednar (1986), " a centroidal, interior, daylit space which organizes a building." T o d a y , a t r i u m designs are complex and their functions, varied. From functions.  the  environmental  perspective,  atrium  spaces  perform  certain  specific  B y default, atria modify the environmental conditions within the a t r i u m well  and the spaces adjacent to it.  F o r example, large expanses of glazed areas along the wall  facade or the roof of a n a t r i u m space provides natural lighting. Because of the nature of sunlight, t h e r m a l benefits or heat gains are associated with it. location,  the  thermal  benefits  associated  exploited or m a y have to be controlled.  with natural  Depending on the climatic  lighting m a y  be modified and  In w a r m locations, heat gain is undesirable, and  required strategies, either by solar control or increased ventilation m a y be adopted to keep it m i n i m u m . In cold climates, a n a t r i u m m a y be used as a buffer space.  Passive heating  m a y be achieved b y direct heat gain i n a n a t r i u m space and b y storage of heat in the t h e r m a l m a s s consisting of a t r i u m floor and the walls bounding the atria.  2  A n a t r i u m space cannot be designed in isolation for a n y one function, ignoring the existence of the others.  T h e type of building, the climatic location and the  economics  involved are significant in designer descisions as to which factor should be given priority. A n y design feature used to enhance  one function should clearly not be detrimental  to  another. T o enhance the atrium space, art forms such as sculptures, m u r a l s , and paintings have been frequently used.  Landscape features such as water and vegetation have also  been used to provide a humanized scale and a soft v i s u a l atmosphere.  T h e i r presence m a y  be essential for aesthetic reasons, but m a y conflict w i t h the environmental performance of an a t r i u m space, for example, lighting levels could be reduced when vegetation is present as it absorbs light. Regardless of the intent of the original design, a n y a t r i u m space m u s t conform with the basic non-energy environmental needs: it m u s t be safe against fire and prevent unwanted sound transmission. T h i s thesis has concentrated savings.  only on daylighting due to its potential for  energy  Regardless of its size, shape or f o r m , atria, by default, serve to daylight the well  and the spaces adjacent to it.  H o w e v e r , it is essential to provide the appropriate  amount  of light for all tasks within the a t r i u m space and the spaces adjacent to it, free f r o m glare and of the right contrast.  T h e lighting system in the work place should provide o p t i m u m  performance, a pleasant working atmosphere and also keep both the operating and capital cost of the lighting system to a m i n i m u m .  Since daylight is variable, it needs to be  supplemented b y artificial lighting. T h e physical characteristics of the space affects its daylighting performance.  The  reflectivity of the walls and floor surfaces, the size, shape and volume, influence the light levels within the atria well and its adjacent spaces. T h i s thesis has been divided into two parts.  T h e first part provides the overview  for the thesis, a n d the second deals with the procedure and the results of the thesis. T h e first p a r t contains two chapters.  3  C h a p t e r one:  Daylighting in Atria, provides  the thesis - it covers the areas of daylighting in atria,  objective  related  research  significant to the study,  lighting  and scope of the thesis.  C h a p t e r two: energy  the background for the substance of  Environmental Role of Atria  phenomena  in a t r i u m spaces.  deals with the  Fire protection  addressed briefly in the non-energy related issues of atria.  non-energy  and acoustics  and  have been  A n d , the basic energy needs of  heating and ventilation, and lighting have also been been discussed. T h e importance of the study of light  wells  to understand daylighting in atria, design  daylighting performance, and the physical proportions,  characteristics,  which defines the concept of the well  to enhance its  such as form, shape, size and  index  physical scale models have been discussed in detail.  of atria  for daylighting studies using  T h e role of the bounding  elements  of the atria: roof, wall and floor to support daylighting have also been studied i n detail. T h e second p a r t also contains two chapters. Chapter model  studies  three:  Methodology  discusses  the  for daylighting analysis. T h e model  design and construction,  materials,  advantages  and disadvantages  used for the daylighting  study:  of the  size and scale of the model, and the measurement process  followed during the course of the study has been dealt with i n detail. T h i s is followed by a section on the daylight  factor,  sky  conditions  and the location  of the model for the  study. The implications.  concluding chapter,  Results:  deals with  T h e last section of p a r t two contains the  the  data  analysis  Conclusion.  and  design  4  PARTI CHAPTER ONE  DAYLIGHTING IN ATRIA  The  use of daylight in a n a t r i u m building requires a detailed analysis of its effects  in the space itself and i n the spaces around it. T h i s involves an understanding of both, the appropriate quantity and quality of light for the w o r k i n g atmosphere. Presently, there is very little information available to fully understand the changes affecting illumination levels in the spaces adjacent to atria caused b y slight modifications in different factors, such as reflectivity and area of openings on the w a l l facade that affect the illumination levels in the well.  T h i s chapter covers the areas of research that is of  significance to the stud3% the objective and the scope of the thesis.  1.0 DAYLIGHTING RESEARCH  D a y l i g h t i n g research embraces two m a i n issues: providing daylight in the space due to its physiological, psychological and aesthetic benefits (Vischer, 1987, and  Roberts,  (Benya,  1982)  1983,  Slocum,  1986  and daylighting as an important energy saving strategy in buildings  Architectural Record,  1983,  Misuriello & Deringer,  1982,  Architectural  Record, 1981).  1.1 Physiological, psychological and aesthetic benefits of daylight The physiological benefits of daylight include the importance of ultraviolet radiation to h u m a n health, the need of changing stimulus to the body and m i n d provided by the  5  constantly changing nature of daylight, a n d the visual contact with nature (Evans, 1987). Being visually separated  from the exterior for long periods can be counter-productive  (Evans, 1987, V i s c h e r , 1987 and Robbins, 1986).  T h e psychological benefits include the  strong desire for direct sunshine i n interiors, view to the exterior, a n d brightness gradient and 'color constancy' of daylight.  T h e brightness gradient and 'color constancy' deal with  daylight as the 'standard' or yardstick against which all things seen b y the h u m a n eye are measured.  T h e aesthetic functions of daylight deal with the sculptural quality of light, the  play of light on surfaces and textures which m a y cast beautiful and interesting shadows. M o s t qualitative  analysis for daylighting has been done on windows, probably  because, traditionally, windows have been the most simple means to provide daylight, view and visual connection with the outdoors. regarding the trade-off between windows a n d the pleasure  energy  A s stated b y V i s c h e r , (1987), definite conclusions loss caused  and satisfaction  b y the poor t h e r m a l  qualities of  windows b r i n g to building users cannot be  d r a w n f r o m existing data. In office environments, lack of windows in the work spaces seems to contribute to various psychological a n d physiological problems (Vischer,  1987, p. 110).  In a study  reported b y Wotton a n d B a r k o w (1983), although there was no significant relationship between worker productivity a n d access to daylight and a r e a of glazing, the sense of wellbeing and job satisfaction seems to be associated with the presence of windows in the work spaces.  If windows are to be provided in a t r i u m spaces, not only do they provide daylight;  in addition, owing to the presence of windows, the a t r i u m well serves as a space to look into for aesthetic a n d for psychological reasons. daylighting,  it is treated as a n y other  If the well is to serve functions other than  "outdoor"  space  and qualities of the outdoor  environment need to be incorporated within the space. C a n a d i a n office building research distinguishes between worker productivity a n d worker  satisfaction.  atmosphere,  While  windows  contribute  to  satisfaction  they do not appear to contribute to the occupants  with  the working  ability to do their work  6  (Vischer, 1987). essential.  Control of daylight at the user's level i n the working environment is  Since people have control (by using adjustable drapes a n d shades on windows)  over the level of light admitted into the space, this seems to be one of the potentially significant contributing factors to worker satisfaction.  1.2 Daylighting research for energy savings D a y l i g h t i n g research for energy savings deals with the issue of admitting daylight into the interior of a space i n such a w a y as to reduce artificial illumination a n d therefore reduce electrical energy consumption.  In general, depending on the building type, energy  savings for daylighting could amount to between  30% to 80% of total energy  operating, depending on peak loads a n d climatic location (Ian, 1985).  cost of  There is no doubt  that if properly provided, daylighting c a n be used to keep the cost of electrical lighting minimum.  D a y l i g h t i n g and energy  performance  have been reviewed i n a number of  buildings which have projected potential energy savings, including schools (Gillet & White, 1985 and A r s e n a u l t & K i n n e y , 1985), office and commercial buildings (Troyer & K u h a r i , 1985, B u s c h & Scheuch, 1983, Cook, 1982 and Place, Fontoynont, K a m m e r u d , B a u m a n , A n d e r s o n & H o w a r d , 1982) or even church buildings (Kroelinger, 1987). The  quantitative aspect of daylighting research has dealt with different computer  programs and simulation techniques for recording a n d studying the effects of daylight on openings on the w a l l facades such as windows (Balcomb, 1987, B o y e r & D e g e l m a n , 1986, S h a v i v , 1985, Johnson, Connell, Selkowitz & A r a s t e r , W i n k e l m a n , 1982 a n d B r y a n , 1982).  1985, Selkowitz, K i m , N a v v a b &  Studies for developing procedures for the calculation  of reflected daylight ( H r a s k a & R y b a r ,  1987, H u n t e r & Robbins, 1985 a n d Robbins &  H u n t e r , 1983) have also been undertaken. Commercial  a n d office  building  daylighting research/practice  determining the level of illumination reaching  has focused on  the working plane a n d the impact of  fenestration on the energy use and peak loads in daylit buildings (Ander & H a s s a n , 1985)  7  as well as the integration of electric light and daylight with the t h e r m a l a n d the electric operations Johnson,  of the building to provide energy & Sullivan,  efficient performances  (Selkowitz,  Choi,  1983, E m e r y , H e e r w a g e n , Johnson, K e p p e n h a n & L a k i n ,  1982,  Place et a l . , 1982,). D a y l i g h t i n g strategies in office buildings indicate that 38% - 40% a n n u a l lighting energy reduction c a n be achieved b y conventional means (Misuriello & Deringer, 1982). In another report, the use of natural and task lighting i n a commercial building projected 50% savings i n auxiliary lighting costs (Architectural Record, 1983).  1.3 Daylighting strategies in atrium buildings A  daylighting strategy m a y be a n integral part of a n energy  strategy of the  structure as a whole or b y default, atria m a y be used to perform daylighting function. T h e simplest means of providing daylight into the interior of the atria well and its adjacent spaces is to provide large areas of glass at the source of light, which m a y be the roof or the wall, or both.  H o w e v e r , daylight is not strictly used only for providing ambience a n d  working illuminance, b u t in most cases, for supporting plant life within atria.  E x a m p l e s of  these are A t r i a N o r t h (Toronto), Deere W e s t (Illinois) and F o r d Foundation H e a d Quarters (New Y o r k ) (Saxon, 1987 and Saxon, 1983). s a v i n g device:  for daylighting, s u m m e r  Some designs use atria as an integral energy  shading, ventilation, a n d winter  heating, e.g.  G r e g o r y Bateson building (Sacremento, California) (Saxon 1987, Bednar, 1985, a n d Saxon, 1983) a n d N o r t h a n d South Enerplex buildings (Plainsboro, N e w Jersey) (Bednar, 1985). Different types of techniques have been used to project light into the interior of the space, which m a y be classified into:  1.3.1.  Traditional Windows,  techniques skylights  and clerestories  daylight into a building interior.  are traditional  techniques  T h e y m a y be used i n atria also.  used  to b r i n g  W i n d o w s m a y be used  8  on the walls of the atria well to admit light into the interior of the occupied spaces. Skylights have been used in the Philadelphia Stock Exchange 1985)  (Philadelphia)  (Bednar,  where steel trusses support skylights to f o r m a gable roof, also in the O l d Post  Office (Washington, D . C . ) (Bednar,  1985)  gable skylight at a different level. (Washington, D . C . ) (Bednar, 1985)  In the E a s t Building of the N a t i o n a l G a l l e r y of A r t a n d in Enerplex (New Jersey), the skylights have been  specially designed for solar control. D a l l a s C i t y H a l l (Dallas) (Bednar,  where the old skylight was replaced with a new  A clerestory-like arrangement has been designed for 1985), in which only north light is admitted into the  interior from vertical members of three half-vaulted monitors.  A p p e n d i x A shows  some  atria buildings in V a n c o u v e r which have used different means to draw light into a t r i u m spaces using different roof forms and orientation, and different materials that have been used on the walls and floor to distribute light within the space. Research has concentrated m a i n l y on sizes, proportions and locations of windows for effective lighting levels throughout the rooms, also avoiding glare, excessive solar gains and providing a view to the outside (Glover, 1982).  Studies on skylights and clerestories  have dealt with the issues of increasing interior light b y using reflected light, reducing glare, and eliminating direct solar gain in the cooling season  (Felts,  1985  and Vonier,  1984) .  1.3.2.  Reflective  techniques  Studies have been done on developing exterior baffles and louvers for introducing uniform lighting i n the interior and reducing the solar gains when not required (Kitchen, 1985) , and using various  methods  for  deep light penetration  such  as  light  plenums  (Mirkovich, 1983), which are light shelves extended into the office space to 'trap' light within the p l e n u m for further reflection,  light shelves which are horizontal  projections  above the view window and below a clerestory used to distribute light in the interior and also serve as a shading device to minimize the penetration of direct sunlight on the  9  FIGURE 1 DAYLIGHTING IN ATRIA  LIGHTING IN AN ATRIUM WELL  LIGHTING IN SPACES ADJACENT TO AN ATRIUM WELL  10  working plane, a n d sloped ceilings (Windheim, Riegel, D a v y , S h a n u s , & D a l y , achieve m a x i m u m light distribution within the interior spaces.  1983) to  Sloped ceilings were used  in conjunction with light shelves in Lockheed Missiles and Space C o . , Inc., (Sunnyvale, California) (Saxon, 1987, Bednar, 1985, Saxon, 1983 and W i n d h e i m et a l . , 1983) . L i g h t scoops m a y also be used to project light into the side spaces (refer to section 7.2.2 of Chapter 2). Tennessee  T h e use of light scoops for beam lighting w a s proposed in the  V a l l e y A u t h o r i t y Office Complex, (Chattanooga,  Tennessee),  (Saxon,  1987,  Bednar, 1985 and Saxon, 1983). L i g h t shelves m a y be used i n the facade facing the atria (interior light shelf) or i n the facade facing outside (exterior light shelf).  A n interior light shelf w a s used in V e n t u r a  Coastal Corporation, (California) and Shell Woodcreek, (Houston) (Bednar, 1985), whereas exterior light shelf w a s used only on the south side in Lockheed Missiles a n d Space C o . , Inc., for controlling glare.  L i g h t shelves c a n be used as a light reflector, for glare control  and as a shading device.  2.0 LIGHTING IN ATRIA  Since the oil embargo i n 1973 a n d the subsequent 'energy crises', daylighting has been linked with energy benefits.  A l t h o u g h it is not possible to generalize the extent to  which the use of daylighting will actually decrease the energy consumption i n a n y building, if provided properly, it will rarely increase the lighting energy consumption. T h e r e are two major considerations i n the use of the a t r i u m for daylighting (refer F i g u r e 1):  a. L i g h t i n g  i n the  atrium well  to provide adequate light for activities within the  a t r i u m only.  b.  U s i n g the a t r i u m as a source of light to provide adequate lighting to the  adjacent to the a t r i u m .  spaces  11  2.1. Atrium well The atrium well has higher levels of illumination compared to the spaces adjacent to it. As in the case of the light well, the illumination levels are highest at the top of the well and gradually decrease towards the floor of the atria (Cartwright, 1985 and Oretskin, 1982).  The  center of the horizontal plane at any  height receives higher levels of  illumination than the sides. This is because the center of the well "sees" a greater portion of the sky than the sides. Within the well, the illumination levels will be minimum along the edges of the floor.  2.2. The spaces adjacent to atrium While it is relatively easy to illuminate the atrium well, it is more difficult to illuminate the spaces around the atria by virtue of their position in relation to the light source. This is more so in the case of lighting the lower levels and its surrounding spaces in an atrium where the source of light is from the roof. The atrium well acts as a means to deliver light to the spaces adjacent to it. Illumination decreases as the depth of atria increases, as light is drawn off at each level, into the spaces adjacent to the atria. Openings on the wall facade will influence the amount of light drawn into the side spaces and at various levels in the well itself. Openings like windows on the walls of the atria act as light absorbers, reducing the light intensity in the well especially in the lower reaches of the atria. Therefore, larger openings will draw more light from the well.  The reflectivity of the atria walls is a  significant factor in enhancing illumination levels, as higher reflectivity of the walls will increase the amount of available light in the well. Thus, reflection may  be used as an effective strategy for enhancing illumination  levels within and in the spaces adjacent to the atria.  12  3.0 OBJECTIVE  T h e objective of this thesis is to assess the relative contributions of changes in the reflectivity and opening sizes on the illumination levels in the side spaces for different well indexes i n atria.  T h e relative importance of the bounding elements of the atria, the wall or  the floor, or both for enhancing illumination i n the spaces adjacent to the atria, is to be determined. Studies conducted b y Cole (1988), C a r t w r i g h t (1985) a n d O r e t s k i n (1982) suggest that the reflectivity of the wall facade and the floor affect the illumination in the atria well, and thereby i n the adjacent side spaces.  Inter-reflection f r o m the floor also seems to play  a key role i n increasing the available illumination i n the spaces adjacent to the atria.  4.0 SCOPE  Atria  perform m a n y  environmental functions.  However,  only the function of  daylighting has been dealt with i n detail. T h e r e are a number of variables involved i n the study.  T h e r e are m a n y different  forms of atria - with different width and length of the well in plan, different sectional schemes, different roof forms, different surfaces and openings i n the w a l l facades. F o r this study, the physical f o r m of the atria is kept constant: i n this research a rectangular, top-lit a t r i u m without a n y roof glazing has been used. the  wall openings also.  adjacent to atria.  Measurements  are taken  N o glazing is used on  at different heights  in the spaces  T h u s the variables involved in the study are:  - the surface treatment of the wall and floor - different size of openings in the walls facing the a t r i u m well. T h e emphasis of this study is to understand how the changes i n the illumination levels are affected in the spaces adjacent to the atria only. T h e purpose of the study is to  13  demonstrate the relative importance of the use of specific reflective surfaces and openings of the atria walls on the light distribution, and utilize the results as a guide for further detailed studies. Fully overcast skies offer the least lighting levels in terms of absolute illumination values. It is very difficult to interpret measurements for varying light conditions occurring under the natural skies, and hence stable overcast sky conditions are preferred. Hence, the study is conducted under fully overcast skies. Using simplified calculation techniques, only the quantitative study of light using photometric measurements have been studied.  Qualitative studies deal with occupant  responses to daylight within the space and significance of providing view to the outside in the occupied spaces, which involves a different area of research beyond the scope of this thesis.  14  CHAPTER TWO  ENVIRONMENTAL ROLE OF ATRIA  T h i s chapter deals with the environmental role of atria.  T w o p r i m a r y aspects have  been considered: non-energy and energy related environmental phenomena.  T h e non-  energy related phenomena are fire protection and acoustics and energy related phenomena are  heating,  ventilating and lighting.  B o t h , the  non-energy  and the  energy  related  phenomena affect the physical form and shape of the atria.  1.0. NON-ENERGY RELATED PHENOMENA  For protection  atria and  design to be safe acoustics  have  to  a n d pleasant, be  taken  non-energy related factors  into  consideration.  like fire  Satisfying  these  requirements will i n v a r i a b l y impact on the daylighting function.  1.1 Fire Protection T h e danger of fire h a z a r d is more pronounced for a t r i u m t h a n for other building types as the a t r i u m space is comparatively large and unenclosed. interconnected spaces directly.  It is linked to all other  D u e to stack action, fire and smoke can easily spread  vertically in this large unhindered space.  A t r i a b y themselves are not usually a source of  fire h a z a r d , and fire can quite easily be detected on account of high visibility within the space.  Smoke control is an area of concern as the fire m a y originate in the  occupied space a n d the smoke m a y spread easily into this large space.  adjacent  If no escape is  15  provided, smoke fill up the occupied zones also.  Therefore, efficient smoke exhaust  systems have to be provided. There are three steps of control needed in the design strategy of the atrium spaces (Saxon, 1987): a. means of escape b. smoke control c. fire control. The means of escape deal with the circulation routes for evacuation in the event of a fire. Since the atria can be easily converted into a smoke reservoir, the exit stairs should be separated from the atria by cut-off lobbies. The entire evacuation process may be designed in three distinct stages (Saxon, 1987 and Bednar, 1985): 1. access to the means of escape through a corridor or room which may or may not be protected from fire 2. the means of escape itself, which is a usually a stair protected from fire by fire resistant walls and door 3. the route to the outside or a safe refuge area. Smoke control is an essential part of the ventilation strategy of the structure as a whole. Smoke control means extracting smoke from the structure by venting. Smoke control is needed to prevent the atria well and the adjacent spaces from smoke-logging. Extraction of smoke depends on the volume of the atria and the type of atria, that is, totally enclosed or open-sided. If the atrium well is open on one or all the sides, extraction may be through the atrium well or through the surrounding structure. If the atrium space is totally enclosed and sealed from the surrounding spaces, the structure may be treated as any other and smoke control strategy need not involve the atrium well at all. The smoke control strategy for such a structure is independent of the atria well. The fire-control and fire-fighting strategy deals with measures to limit the spread of fire within the structure and to the adjoining structures as well. The most important  16  requirement is the early detection of fire. Detection within the a t r i u m space is difficult as detectors placed on the top of the well cannot detect fires on the floor.  Restricting flame  spread is dependent on whether the atria is totally enclosed or open on any side.  While  fully enclosed a t r i a are efficient for smoke control, they are not for flame spread, as floor to floor spread is faster in this case t h a n for the open sided atria.  T h e final outcome of  a n y fire eventually lies in the hands of the fire department, for which quick and safe access to the fire is required.  Service access for the fire engine m u s t be provided around  the building. Building  codes  and regulations  state the  specifications for  fire  detection,  fire  suppression, fire a l a r m , smoke control and emergency power, materials to be used, fire ratings of the a t r i u m enclosures, a t r i u m exit and interior finish, a t r i u m size and use which varies  depending on the  height and number of stories  of the  a t r i u m building.  The  materials used a n d the size/shape of the atria designed specifically for fire protection m a y adversely affect the performance for daylighting. 1.  A smoke reservoir at the top of the atria well are recommended when smoke  exhausts through the a t r i u m well is desired.  If the occupied zones on spaces adjacent to  the atria are open to the well, the smoke will travel into the well, rising to the top and filling  the a t r i u m space.  If the smoke reservoir is not provided, the smoke which collects  at the top can spread to the other floors. A smoke reservoir collects the smoke a w a y f r o m the occupied zones, which can be exhausted f r o m vents on the sides. smoke c a n be exhausted by mechanical means.  A l t e r n a t i v e l y , the  T h e height of the smoke reservoir varies,  but a m i n i m u m of 1.7m from the highest exposed floor to the centreline of the vent has been recommended (Saxon, 1987,  p. 126).  U s i n g a smoke reservoir increases the overall  height of the atria well, which increases the distance for light to travel into the lower reaches of the atria.  T h e roof system chosen will have to be designed to incorporate the  vents of the smoke reservoir, placing restrictions on the type of roof of the atria well.  17  FIGURE 2 SMOKE EXTRACTION VIA ATRIUM SPACE  SMOKE RESERVOIR  VENTS FOR SMOKE  SMOKE PLUME (15 DEC) EDGE SCREENS  LIGHT SHELF (20 DEG.) DIFFERENT FLOOR EDGE PROFILES TO PREVENT SMOKE ENTRY  18  2. Enclosing the atrium from the adjacent spaces offers a very effective means of limiting fire and smoke spread. But this is not desirable for both lighting and aesthetic reasons. Also, for daylighting, the barriers between the well and the surrounding must not be opaque. Glazed surfaces may be provided, but they do not prevent heat radiation while opaque barriers do. If glazing is to be used, intumescent laminated glazing which turns opaque in fire, thus blocking radiation is preferred (Saxon, 1987, p. 99). The 1984 BOCA (Building Officials and Code Administrators International) Basic Building Code requires that the glass should not have any barriers such as curtains and drapes to keep the water from wetting the surface. Where barriers have to be provided for protection against glare, this may present a problem. 3. Balconies and terraces opening into the atrium well must also be protected by barriers, unless they are intermittently used or function as "break areas". The openings between the well and the overhang spaces should have barriers upto cill height at least, so that people can crawl past the barrier in the event of a fire. Barriers made of glazing which are suitable for daylighting may be used, but of the laminated type, for protection against heat radiation. 4. The design of the profile varies depending on the type of atria (height, width, mechanical ventilation system used), and the system adopted for smoke extraction. Where the extraction is through the atrium well, there are some general rules to be followed (refer Figure 2): a. Floors that are set back with every increase in level protect themselves. This type of arrangement of the floor is also advantageous for lighting as more area is exposed to the sky vault. b. A fire and smoke barrier along the perimeter and at least 0.45m from the ceiling of each floor and opening into the atrium well is used to keep the smoke from spreading to that floor along the ceiling. There is a similar projection from the floor called the 'floor  20  edge' used to prevent spread of fire f r o m the lower floors. These edge screens m u s t not be too big so as to allow sufficient entry for make-up air in the event of a fire. c.  T o prevent smoke entry into side spaces (refer Figure 2), the edge screen from  the ceiling should cut the 15 deg. angle (as the smoke plume expands at approximately  15  deg. to the vertical) f r o m the floor edge and light shelves, if any, should not cut the 20 deg. angle (Saxon, 1987).  1.2 Acoustics One of the m a i n concerns in a n y kind of design is to avoid conflicts between other functions that the space m a y be required to perform. working environment, it is necessary to have compartments  In office spaces, to ensure a quiet  acoustical  separation between the office  and the circulation spaces, and also between noisj mechanical equipment r  and the working area.  T h i s m a y conflict with a n a t r i u m space that m a y be designed  p r i m a r i l y for daylighting function.  A l t h o u g h the basic properties of light a n d sound are  analogous, the design requirements for the two are different. In designing for light and sound in atria, one essentially deals with contained light and sound. W i t h i n the well, the sound can be 'moderate' to 'loud', measured on the a t r i u m floor predominantly f r o m speech or f r o m office activities, ranging between 50 d B to 70 d B (Egan, 1988,  p. 13).  M o s t often, noise due to mechanical equipment is physically isolated  f r o m the m a i n w o r k i n g areas.  Since the a t r i u m space is typically larger than the adjacent  spaces, the sound waves can be easily enhanced by reflection if there are no absorptive surfaces.  Therefore, prevention of sound transmission f r o m the sound source is required  (refer F i g u r e 3). Since a n a t r i u m space is comparatively large, the reverberation time for sound is increased, hence "time period" for decay of the sound is longer. the space to be intensified.  T h i s causes noise levels in  Therefore, necessary strategies will have to be undertaken to  reduce the reverberation time.  T h e reverberation can be reduced b y incorporating sound  21  absorbent  surfaces.  These m a y be in the  form of porous plasters  as  wall finishes,  decorative hangings and blinds even, the use of dense planting. Noise is unwanted sound, and in office buildings, quiet working conditions  are  recommended.  H o w e v e r , there should be some background or m a s k i n g sound, not " p i n -  drop" silence.  In large offices, the preferred range or noise criteria is between N C - 3 5 to  N C - 4 0 and equivalent d B A levels of 42-47 (Egan, 1988, p.  1.2.1  233).  Reflection Reflectivity is surface-dependent for sound. T h e inherent physical properties of the  material determines its capacity to absorb or reflect sound. Sound reflection is dependent on the " w a v e length" of sound wave f r o m the source and the dimensions of the surface reflecting the sound waves. are  equal to the  "wave  length" of the incident sound wave,  randomly distributed from the surface (diffusion).  If the surface dimensions the reflected  waves  are  T h e reflected waves bend through a n  opening or around the object when the dimension of the surface is less than that of the incident sound wave (diffraction).  If the dimensions of the surface is about four times the  wavelength of the incident waves, then sound is reflected specularly f r o m the surface. Sound reflection is also dependent on the characteristics of the reflecting surface. T h i s is a more significant aspect than the shape or dimensions of the reflecting surface.  If  the reflecting surface is made of rigid, non-porous materials such as glass, concrete and wood, the sound waves are reflected f r o m the surface.  Porous materials such as carpets,  drapes, and upholstered furniture are very good sound absorbers.  Reflecting glasses are  often used for enhancing illumination, but they also enhance sound in the space, raising the noise level.  T h e r e is also some importance regarding the thickness, density  (porosity)  and method of mounting, that is, with or without airspace behind the surface material.  22  1.2.2  Absorption Sound absorption is the loss of sound energy through the interconnected pores of  the material due to friction with consequent heat gain (not likely measurable).  Materials  that are good sound absorbers are not good sound insulators, as these materials allow sound energy to pass through the surface of the m a t e r i a l . reflect sound, absorbed.  so do rough surfaces,  Smooth and h a r d surfaces  however, if the material within is Fibrous, it is  T h e thickness and mounting of the h a r d surfaces, and the air space behind m a y  still act as absorbers for low frequency sounds. Usually,  sound absorbers are  mounted with a covering panel to protect  surface from possible mechanical/physical damage.  their  H o w e v e r , if the surface is not likely to  encounter mechanical/physical damage, as for most surfaces 8 feet f r o m the floor level, covering panel is unnecessary. W i t h i n the atria well, the materials used for shades and blinds for solar control may  also  serve  as  sound absorbers,  if they  have  sufficient thickness and porosity.  Decorative hangings m a y also be used as sound absorbers. Vegetation are effective for glare control by absorbing light, but are not effective sound absorbers i f the depth is less t h a n 3 0 m .  If a thin layer of vegetation is to used, it  should have a layer of absorptive surface backing to be an efficient sound absorber.  The  type of vegetation m u s t also be considered; deciduous trees are v e r y poor sound absorbers and dense, evergreen vegetation, slightly better.  1.2.3  Transmission If the sides of the atria well are open, there would be 100% sound absorption into  the occupied spaces, that is, complete transmission.  If a n y form of barrier is used, sound  is reflected, depending on the nature of the surface.  T h e thickness of the surface and its  density are important criteria for sound transmission.  23  Certain types of sounds such as those due to fountains or cascades are welcome sounds.  In atria where the side walls are completely open they m a y be transferred to the  occupied zones around as ambient or background levels, but the magnitude of this should not exceed the recommended N C levels for the office space.  1.2.4  Shape  and  volume  T h e shape of the surface affects the behavior of reflection of sound waves, not in the quantity of the sound energy but in the direction of the reflected waves. surfaces are poor sound reflectors as they focus sound.  Concave  O n the other hand, convex or flat  surfaces scatter the reflected sound waves diffusively.  H o w e v e r , this m a y not be so  significant in a t r i u m spaces as they would be in " l i s t e n i n g " rooms such as auditoriums. A l t h o u g h the shape makes considerable difference to the distribution of sound in the space, the key problem is the reduction of sound energy, that is avoiding reflection v i a use  of  absorptive materials/surfaces  in the  space.  This  brings conflicts with  the  daylighting function of atria. 1.  Different shapes of atria m a y be used to enhance lighting in atria which affect  sound.distribution in the space, but the most critical factor is the physical characteristics of the surface lining the walls a n d the floor of the space. are used to reflect light, but these also reflect sound.  U s u a l l y , smooth and h a r d surfaces T h e color of the surface does not  affect sound energy in the space, but it enhances illumination. 2.  C e r t a i n elements used for aesthetic reasons or for solar control, such as blinds  and shades, decorative hangings, and vegetation m a y also be used for acoustic control. W a t e r m a y be used to enhance illumination as well as provide a m a s k i n g sound. V i s u a l l y , it often serves as a n aesthetic element in a t r i u m spaces.  B u t it m a y cause glare,  in which case necessary precautions will have to be t a k e n . T h e function of all these elements in the a t r i u m space has to be decided and their positions, materials/mounting techniques have to be designed accordingly.  24  3.  T h e noise f r o m the floor of the atria c a n be controlled b y using balconies and  overhangs facing the well.  T h e sound waves striking the projections are diffracted.  They  f o r m shadow zones on the side of the occupied spaces, isolating sound f r o m the atria floor. If the sides of the projections are lined with sound absorbing materials, the noise levels can be further reduced (upto 10 dB). Balconies,  overhangs  and such  similar projections  available for reflection, enhancing reflection, but they  increase  the surface  area  also form shadow zones in the  spaces below.  2.0 ENERGY RELATED PHENOMENA  T h e atria that were built before the oil embargo in 1973 focused solely on the aesthetic quality and social function of the interior spaces ( L e h r m a n , 1984, p.20, Saxon, 1983, p.5, H a w k e s , 1983 and Collymore, 1980).  A t r i u m spaces i n hotels a n d shopping  malls were designed for the public, to attract large numbers of people to increase commercial value.  their  T h e y were huge spaces where people could meet a n d talk, a n d often  had elaborate furnishings a n d eating areas incorporated within.  These atria were designed  m a i n l y for their aesthetic value with lush planting, r u n n i n g or still water,  sculptures,  m u r a l s , paintings, etc. M a n y atria built throughout the late 1970's a n d the 1980's also continued to be designed on aesthetic grounds, b u t there was a n increasing awareness of the energy benefits,  which i n m a n y  examples  (Enerplex  in N e w Jersey,  C h i l d r e n s ' Hospital in  Philadelphia, T h e A t r i u m on the B a y s h o r e i n F l o r i d a (Bednar, 1985), to name a few) have incorporated energy conscious design. W h a t e v e r energy savings a n a t r i u m can provide to a building or complex usually takes the form of daylighting spaces adjacent to a n a t r i u m . H o w e v e r , the v e r y presence of the atria does not guarantee energy efficiency in the structure.  T h e a t r i u m design has to  25  be integrated with the  passive techniques and mechanical systems of the structure.  While  there have been m a n j ' examples that have shown energy savings (Architectural Record, 1982,  A r c h i t e c t u r a l Record, 1981  and Collymore, 1980  ) the presence of an a t r i u m does  not automatically reduce energy consumption (Baker, 1988, The  p.40).  energy related functions an a t r i u m involve are heating and ventilating, and  lighting.  2.1 Heating and Ventilating The  heating and the ventilating strategies are often designed together. Depending  on the climatic location, a n atrium m a y perform p r i m a r i l y as (Saxon, 1983, a.  pp. 84-91):  a w a r m i n g a t r i u m - an a t r i u m to collect and transfer heat, or supply preheated  air to the adjacent spaces, decreasing heat losses f r o m adjacent spaces and in the well itself by t r a p p i n g w a r m air from spaces around the atria (compared to the heat losses directly to the outside) b.  a cooling a t r i u m - an a t r i u m to serve as shade in s u m m e r and cross ventilating  space or single sided ventilating space in s u m m e r or in w a r m latitudes c.  a convertible a t r i u m - an a t r i u m that does both: provides w a r m t h in winter and  provides shade or prevents overheating in s u m m e r . In very hot climates, an a t r i u m has to serve a cooling function for most p a r t of the year.  O v e r heating of the atrium is avoided through orientation and shading.  m a y also be achieved by using the atria to induce cross ventilation.  In cold locations, the  emphasis should be to provide w a r m t h during most months of the year. certain  type  of structures,  such as  shopping malls,  Comfort  H o w e v e r , in  it is likely that heat surplus is  generated b y people and use of artificial lighting and m a c h i n e r y .  In temperate climates,  buildings are required to be heated in the winter and cooled in the s u m m e r , and for these atria, the t h e r m a l a n d ventilation functions are required to change over the year.  26  One important factor to be noted is whether the a t r i u m is designed to act as a buffer space or is intended to be a zone where n o r m a l occupancy conditions are met. T h e buffer space provides only a tempered climate, and hence would require further refinement to its services to ensure comfort i n the space. In  buffer spaces especially, w a r m air m a y be collected on the upper levels (the  w a r m air h a v i n g the tendency to rise), a n d hence fans will have to be used to redirect the heated air downward, so that the air m a y be used effectively.  Blinds a n d other shading  devices m a y be used for shading in the s u m m e r , a n d where the atria are required to be cooled, courtyard principle for cross ventilation is c a n be applied. The  ventilation air flow m a y be designed to move f r o m the a t r i u m well to the  surrounding spaces, or conversely from the adjacent spaces to the a t r i u m well, or it m a y recirculate between the two. T h e latter provides the m a x i m u m savings i n t h e r m a l energy (Baker, 1988). and  T h i s m a y be done b y simpty opening the windows between the a t r i u m well  the occupied  spaces.  However,  a certain  amount  of fresh  air will have  to be  continuously supplied, to avoid the air becoming too stale, since it is constantly being circulated between the well and the occupied spaces. retain freshness to a certain extent.  Vegetation, if provided, helps to  If a n a t r i u m and its adjacent space are independent  of each other, that is, each has its own separate heating and ventilating scheme, the energy consumption of the structure will increase (Baker,  1988).  2.2 Lighting F o r the atria to function as a building element that reduces energy consumption, it m u s t reduce the lighting, heating and air conditioning costs of the complex as a whole. F o r office buildings i n N o r t h A m e r i c a , lighting represents the largest portion of the total energy load (Robbins, 1986, p. 7, G a r d n e r , 1984, a n d Misuriello & D r i n g e r , 1982). the need to focus on lighting as a major means of energy savings.  Hence,  27  FIGURE 4 NATURAL LIGHTING IN ATRIA  DAYLIGHT  28  A p r i m a r y role of atria is to deliver useful levels of natural light to the atria and its adjacent spaces.  A l t h o u g h energy savings is the m a i n reason for favoring daylight, there  are other reasons also (Selkowitz & Johnson, 1980,  p. 15,16).  1. In m a n y utility service areas, commercial building owners are required to pay, in addition to p a y m e n t s for total electrical consumption, a demand charge which reflects the peak d e m a n d of the building for each month. reduce  the  use  of  electric  lighting,  which  in  U s i n g natural lighting effectively will turn  will  decrease  the  peak  energy  consumption, required for both heating and cooling. U s i n g windows to provide n a t u r a l light in the work space reduces dependency  2.  on electrical  systems.  Also, if these windows are  operable,  it allows the user to be  independent of the mechanical ventilation systems in the event of a breakdown. An  atrium  provides the designer  with an opportunity  thereby reduce the costs of operating electrical lighting.  to exploit daylight,  T h e intensity and distribution of  daylight can be controlled b y orientation and b y architectural devices such as U s e r control devices  such as blinds and shades; even overhangs m a y  control the distribution of light. reflectances and furnishings.  function  as  fenestration.  also be used to  W i t h i n the interiors, the factors affecting this are surface Some type of solar control is needed to reduce solar heat  gain during the hot months of the y e a r . s y s t e m is capable  and  T h e control systems m a y be dynamic wherein the  of responding to the changes in the sky conditions.  selective light transmitters,  admitting  S u c h systems  only diffused light and not  direct  sunlight. While considering natural lighting in atria, it is essential to distinguish between sunlight  2.2.1  and daylight  (refer F i g u r e 4).  Sunlight T h i s is the  conditions.  direct light  falling on the building during clear or partially clear sky  Sunlight is highly dynamic  and follows defined daily and seasonal paths  29  relative  to the building.  Sunlight penetrating  through  the openings  c a n serve as a  powerful and highly dynamic illuminant as well as a source of useful winter heat (Cole, 1989). H o w e v e r , this c a n also create problems of glare a n d adverse overheating.  G l a r e is  excessive brightness that causes discomfort and reduces visual perception. Overheating is a problem that has to be dealt w i t h p a r t i c u l a r ^ in the hot months of the year.  In winter, the heat produced due to direct sunlight c a n be used to heat not  only the atria, b u t also the adjoining spaces. In s u m m e r , diffused instead of direct sunlight is preferred. blinds',  T h i s c a n be achieved b y using solar shading techniques such as shades a n d  movable  appropriate  louvers  to intercept  direct  design of roof and selection  sunlight.  It could also  of glazing types.  These  be achieved b y  issues  have  been  addressed in detail i n section 7.0 of this chapter.  2.2.2  Daylight T h i s is the diffuse light that comes f r o m the complete s k y vault that envelopes the  building. 1989).  D u r i n g overcast s k y conditions, buildings are bathed i n daylight alone (Cole, Overcast  conditions can also  cause problems  of glare.  If this  glare  c a n be  minimized, daylight c a n be used to provide w o r k i n g illuminance in the interiors. In temperate climates, cloudy skies dominate for most p a r t of the year.  These  skies have greater luminance at the zenith than at the horizon. T o p lit atria are therefore preferred, with a clear unobstructed glazed roof for m a x i m u m transmission of light.  This  would provide the m a x i m u m use of diffuse light f r o m all parts of the s k y .  3.0 LIGHT WELLS  A t r i a a n d light wells are v e r y similar i n design. B o t h deal with the issues of admitting light to the lower levels, a n d ultimately, in the f o r m of suitable a n d useful light  30  FIGURE 5 LIGHT WELL AND ATRIUM  t  __J  [• -.1  UGHT WELL  ATRIUM  •A  31  FIGURE 6 ATRIA DESIGN TO SUPPORT NATURAL LIGHTING  ROOF FORM  .SURFACE TREATMENT OF WALL  o  UJ  x  SURFACE TREATMENT OF FLOOR WIDTH  32  into the spaces that are adjacent to it (refer F i g u r e 5). Since the light well has no physical barrier at the light-source, there is no solar control.  Solar control c a n be achieved only at  the next level, at the openings in the walls facing the well. T h e study of the light wells m a y f o r m the basis of daylighting study i n a t r i u m spaces (Giovani, K r o n e r & Leslie, 1986).  Studies b y C a r t w r i g h t (1985) and O r e t s k i n  (1982) concentrate on the changes in the illumination levels between the top a n d the bottom of the light well, and the effects of their sizes on illumination levels in the well and in the adjacent spaces.  C a r t w r i g h t ' s study indicates a simple relationship between the size  of the light well, and the daylight level i n the adjacent spaces.  Bigger the size of the well,  higher are the light levels in the well and the spaces adjacent to it. T h e study b y O r e t s k i n shows that for similar volumes a n d areas of the well, those with elongated plans have lower illumination levels when measured at similar points.  Windows in the center of the  well receive more light than those at the corners.  4.0 DESIGN OF ATRIA  T h e design of a n a t r i u m to provide n a t u r a l lighting depends on (refer F i g u r e 6): a.  fenestration system of the roof  b. orientation, of the roof in top-lit atria and of the walls i n side-lit atria c. the relative proportions of the length, width a n d height of the atria. d.  a t r i u m wall surface treatments  c. the treatment of the atria floor, i.e., presence of plants and water T h e means b y which natural lighting is effectively used, which m a y be divided into three distinct areas: 1.  H o w light is brought into a n a t r i u m .  fenestration  system of the roof.  determinants.  In top-lit atria, this is dependent on the  In side-lit atria, fenestration  a m d orientation are the  33  FIGURE 7 DIFFERENT TECHNIQUES FOR ADMITTING LIGHT INTO ATRIA  TOP LIGHTING  SIOE LIGHTING  LATERAL LIGHTING  34  FIGURE 8 GENERIC FORMS OF ATRIA  TOP LIT ATRIUM  LATERAL ATRIUM  35  2.  H o w the light is distributed into a n a t r i u m .  T h i s is dependent on the relative  width, length and height of the atria, and the surface treatments of the atria wall and floor. 3.  H o w the light is collected and delivered effectively to the w o r k i n g plane of the  occupied spaces and within the a t r i u m itself.  T h i s is dependent on the a t r i u m w a l l surface  treatments, the sectional scheme (such as projecting terraces and balconies, light scoops, etc.). Inter-reflection  seems to be the most important factor responsible for providing  working illuminance within the atria well and in the occupied spaces adjacent to it (Bednar, 1985 and N a v v a b & Selkowitz, 1984).  5.0 PHYSICAL CHARACTERISTICS OF ATRIA  T h e quantity of light admitted into a n a t r i u m is dependent on the f o r m of the atrium.  S i m i l a r spatial forms m a y use different strategies for admitting light into an  atrium.  Generally, light is admitted into the a t r i u m u s i n g the following strategies (refer  F i g u r e 7 and A p p e n d i x A ) : a. T o p lighting: where light is admitted from the top of the a t r i u m only. b. Side and lateral lighting: where light is admitted f r o m the sides of the a t r i u m . Often atria designs incorporate not just one of these methods in isolation, but a combination of top and side (lateral) lighting methods. It is difficult to classify atria into a n y specific category such as linear, closed, opensided, lateral, multiple lateral or partial atria. category exist, leading to hybrid arrangements.  T h i s is because m a n y variations of a n y one H o w e v e r , some generic forms exist, which  are shown in F i g u r e 8. T h e atria space that is created between the occupied spaces around the atria well is dependent on the proportions of the space, shape and volume and the overall design of the  36  FIGURE 9 ATRIA PROPORTIONS IN PLAN AND SECTION x  X  to z UJ  PLAN  WIDTH  PAR =  LENGTH  X  o UJ X  WIDTH  •x  SECTION SAR =  HEIGHT WIDTH  W I D T H  X  37  roof, walls a n d floor of the atria well.  However, the factors  influencing this are  site  restrictions, building p r o g r a m and the energy strategy.  5.1 Proportions In the use of atria for daylighting, the proportions in plan a n d section have to be considered (refer F i g u r e 9) (Bednar, 1986, p. 66). The  proportions of the atria, called the  a m o u n t of light in the atria. length of the atria floor. width of the atria well.  T h e plan  aspect ratios by B e d n a r determine  the  aspect ratio ( P A R ) is the ratio of the width to the  T h e section aspect ratio ( S A R ) is the ratio of the height to the Therefore, for rectangular atria, the P A R is between 0.40  and for square atria, it is 1.00.  If the P A R is less t h a n 0.40,  -  0.90  the atria is called linear.  A  linear plan generates the largest perimeter for the least enclosed volume followed b y triangular, square, and the least by circular plan (Bednar, 1985). has a very shallow a t r i u m and S A R of 2.00  S A R of less t h a n  1.00  has a very tall and n a r r o w a t r i u m .  For  effective daylight penetration, S A R between 1.00 - 2.00 is sufficient. T h e S A R plays a major role in determining the amount of n a t u r a l light reaching the floor and the spaces around the atria. h a v i n g wells w h i c h are  A t r i a that have high S A R values, that is, atria  very tall and narrow will not be v e r y effective for daylight  penetration to the bottom of the well.  O n the other hand with v e r y s m a l l S A R , light  penetration to the bottom of the well a n d to its occupied spaces is relatively easier.  For  daylight to reach the bottom of v e r y tall atria, the reflectivity of the walls becomes an important factor in the distribution of light i n the well and the adjacent spaces. For  lighting, one large well of a given area is more effective than several s m a l l  wells, totaling the same area (Oretskin, 1982).  F o r a given area in plan, illumination  m e a s u r e d at the a t r i u m floor will be greater for the one in which the depth of the well is smaller.  If wells of equal area, but different shapes are compared, wells of circular plan  38  receive more light at a given level followed by square and rectangular  plans (Oretskin,  1982).  6.0 WELL INDEX  F o r the purpose of daylighting studies, it is not possible to examine atria of so many  different  forms,  shapes/volumes  since  there  has  to  be  some  standard  of  measurement. Traditionally, the concept of well index has been the single most effective means to analyze n a t u r a l lighting efficiency in light wells and atria.  F o r daylighting studies using  physical  to  scale  models,  well  indexes  have  been  used  standardize  the  various  configurations of atria/light well. The The  illumination within a n a t r i u m is related to the dimensions of the atria well.  behavior of light in the adjacent spaces is also expressed  as a relationship to light  levels in atria well, since light levels in the adjacent spaces are dependent on the physical dimensions of a t r i u m . It is expressed b y the well index, given as,  well index = H x ( W + L ) 2 x W x L where, W is the width, L is the length of a t r i u m well in plan and H , the height of a t r i u m well. The f o r m u l a for the well index is applicable only to top-lit atria.  7.0 BOUNDING ELEMENTS  The  floor  architectural elements defining an a t r i u m space are the  roof, the walls  and  of an a t r i u m . These, collectively, m a y be used to modify the lighting conditions in  39  FIGURE 10 SELECTION OF ROOF GLAZING AFFECTS LIGHTING IN ATRIA N  M  CLEAR AR GLAZING  11  N  7/\  CLEAR GLAZING GLA  CLEAR GLAZING  CLEAR GLAZING  CLEAR GLAZING ON THE NORTH  CLEAR GLAZING ON THE NORTH  CLEAR GLAZING ON THE SOUTH  CLEAR GLAZING ON THE SOUTH  N CLEAR GLAZING  / . ] \ I  S REFLECTIVE GLAZING  CLEAR GLAZING  J ^ N T \ |N\  S  \  S  \ I  REFLECTIVE GLAZING  CLEAR GLAZING ON THE NORTH  REFLECTIVE GLAZING ON THE NORTH  REFLECTIVE GLAZING ON THE SOUTH  CLEAR GLAZING ON THE SOUTH  N REFLECTIVE GLAZING  CLEAR GLAZING  REFLECTIVE GLAZING  CLEAR GLAZING  REFLECTIVE GLAZING ON THE NORTH  CLEAR GLAZING ON THE NORTH  CLEAR GLAZING ON THE SOUTH  REFLECTIVE GLAZING ON THE SOUTH  REFLECTIVE GLAZING ON THE NORTH  REFLECTIVE GLAZING ON THE NORTH  REFLECTIVE GLAZING ON THE SOUTH  REFLECTIVE GLAZING ON THE SOUTH  CLEAR GLAZING ADMITS DIRECT SUNLIGHT ALSO REFLECTIVE GLAZING ALLOWS ONLY DIFFUSE LIGHT  40  FIGURE 11 DIFFERENT TYPES OF ROOF FORMS  FIGURE 12 ROOF ORIENTATION FOR THERMAL BENEFITS  NORTH FACING ROOF: DIFFUSE LIGHT  SOUTH FACING ROOF: THERMAL GAINS  42  the well a n d in the adjacent occupied spaces.  T h e level of illumination finally reaching the  working plane is due to the performance of the size/shape/materials of these elements.  7.1 Roof T h e design of the roof is essential to ensure that the appropriate amount, direction and the right combination of sunlight and daylight is provided in the space ( K i m & Boyer, 1986). used.  T h e design of the roof includes its form a n d shape, and the type of glazing material S i m i l a r roof designs will have different lighting levels in the interior for different  orientations, and when placed in different locations.  7.1.1.  Glazing  materials,  form and  shape  U n d e r cloudy sky conditions, clear-glazed, horizontal skylights will b r i n g in the most daylight, since the sky dome is the brightest at the zenith. however,  solar  control will be needed.  In s u n n y conditions,  In winter in cold climates,  direct sunlight is  desirable for passive heat gain, whereas in s u m m e r , solar control will be needed to prevent the atria from overheating.  T h e type of glazing used on the roof in combination with its  f o r m and shape, will affect the quantity, quality and distribution of light within the a t r i u m . This  will  have  requirements  a  direct  impact  (refer F i g u r e  10).  on  the  availability of  S h a d i n g in the  light,  to  roof itself m a y  meet greatly  the  working  reduce  the  transmission of diffuse light under overcast conditions, unless a dynamic system is adopted to respond to the changing sky conditions. V a r i o u s types of roof configurations are shown in F i g u r e 11.  Saw-tooth skylights  with vertical glazing facing the north or south are most effective under clear sky conditions (refer F i g u r e 12).  If the vertical glazing faces the south, sunlight admitted will be very  intense and d y n a m i c . In summer, owing to the relatively higher position of sun in the sky, direct light in the interior will be v e r y little through the vertical glazing. V e r t i c a l glazing on the north provides even and diffused light throughout the year.  43  Side glazing, as in lateral atria lighting the  atria  well.  does not provide the most effective means  U n d e r sunny conditions, the  decreased due to neighboring obstructions.  availability of daylight m a y  of be  Reflective glazing m a y be used to control glare  under sunny conditions, but this also restricts the amount of available light.  Lantern  lighting, which means using clerestories for distributing light in the atria m a y be used in hot climates where direct sunlight has to be excluded for most parts of the year and, only diffused light admitted.  T h e clerestories are  used to collect light f r o m the sides and  diffusing glass on the inner surface of the roof are used to transmit the light through the well.  7.2. Walls T h e reflectivity of the walls and the facade arrangements of atria influence the light distribution in the well, and in the occupied spaces around the well.  7.2.1  Wall  reflectivity  L i g h t incident on a n opaque object is reflected or absorbed.  Reflection for light, like  sound, is dependent on the inherent physical properties of the material: color and surface texture of the material. L i g h t colored surfaces (high reflective capacity) reflect light more than dark colored objects.  White paint has a reflectivity between 70% to 90%,  between 60% to 83%,  and white porcelain enamel  whereas red brick on an unpainted wall has a reflectivity between  10% to 20% (Egan, 1983,  p. 27).  Therefore, using light colored paints on the material of  the atria wall facade, white color or similar surfaces will provide diffuse light for ambient lighting conditions in atria.  Significant increases in the illumination levels in the well will  provide subsequent increases in the adjacent spaces also.  T h e r e m a y be changes in the  reflectivity of the surface depending on shade of the colour, for example, 'diamond blue' has a reflectance of 86.5% and 'delft blue' of  7.8%.  44  M a t t e , rough or heavily textured surfaces reflect light diffusively, scattering light evenly in all directions. capacity.  T h e surface  texture of material  also dictates its  reflective  F o r example, for Crescent board materials, depending on whether the surface is  smooth and glossy or matte, white colour m a y have a reflectivity anywhere between to 90%  (Robbins, 1986,  p. 751).  Smooth white plaster has a reflectance of about  while rough or stippled has a reflectance of 40% (Robbins, 1986, p.  96% 80%,  750).  Reflective glazing or mirrors on the atria facade will also increase illumination levels in the well.  Reflective glasses have a reflectance between 20% to 30%,  tinted glazing of 5% to 10%.  and clear or  If transparent glazing is used in the lower levels m a x i m u m  light will be projected in the interior.  A l t h o u g h reflective  glasses have been used  as  strategies to reflect light, they are not considered as a n effective strategy of transporting light down f r o m the top of the well (Saxon,  1983).  T h i s is because the light is reflected  specularly, i.e., reflected in one direction only, and can be a source of glare within the well. T h e r e are thus, considerable differences in the lighting levels in the atria depending on the reflective materials and surfaces used. While the upper levels of the atria can avail direct light, the Windows  and  lower levels are  similar openings  dependent on light reflected on  the  atria  facade  act  as  from the  upper levels.  light absorbers.  Light  transmitted is used for lighting the spaces beyond these openings by further reflection of the walls, floor and ceiling in these spaces.  Openings on the wall facade decrease the  surface area available for reflection. Ideally, if there are complete wall facades around the atria, with no openings, no light will be 'lost' to the adjacent spaces, and supported by highly reflective walls, there would be m a x i m u m light within the lower reaches of the well.  A c t u a l l y , at each level,  light is d r a w n off into different levels a n d its intensity decreases, until it attains m i n i m u m values at the lowest level.  T h e relative sizes of the openings is thus, important and the  design of the facade should acknowledge the difference in the daylight levels in the top and the bottom of the atria (refer F i g u r e  13).  45  FIGURE 13 VARIABLE OPENINGS ON ATRIUM FACADE TO ACKNOWLEDGE THE DIFFERENCES IN DAYLIGHT LEVELS  46  FIGURE 14 FACADE ARRANGEMENTS TO PROMOTE NATURAL LIGHTING  STEPPED SECTIONS  Jll  LIGHT SCOOPS  PROJECTIONS  47  7.2.2. Facade  arrangements  While a stepped section can be a useful design device for receiving direct light when the section below projects from the one above it, it also makes the floors deeper,  hence daylight penetration  into the spaces beyond becomes  successively  more difficult.  A  reversed stepped section on the other h a n d shades the one below it, which is advantageous when direct sunlight has to be controlled.  Balconies and terraces projecting from the  facade m a y be used as surfaces for reflecting light.  Strategically placed niches in the wall  facade m a y be used as light pockets for providing light to the lower levels of the atria, and also in the spaces adjacent to it. B u t the spaces below the projections act as shadow zones. L i g h t scoops m a y be used on the projecting facade to enhance reflectivity in the well, and therefore  in the spaces around it as was proposed in the Tennessee  Complex (refer F i g u r e 14). enable  L i g h t is projected back to the ceiling using the light scoops to  u n i f o r m distribution throughout  absorbers to control glare.  Valley Authority  the space.  Vegetation m a y be used as light  B u t , if not used properly, it m a y absorb useful light, leaving  v e r y little for further reflection.  7.3 Atrium Floor T h e floor of an a t r i u m plays a n important role in lighting spaces adjacent to the atria at the lower levels (refer F i g u r e 15).  L i g h t reaching the ground is dependent on the  reflective quality of the upper surfaces.  L i g h t reaching the working plane within the  adjacent spaces on the lower floor depends on the reflective quality of the ground.  It is  also crucial to understand w h a t parts of the floor area are essential for increasing the illumination levels.  It m a y be quite possible that only a small p a r t of the floor provides  majority of the reflected light. a. T h e colour of the floor can significantly raise the illuminance in the adjacent spaces at the lower levels (Cole & H u i , 1988). L i g h t colored finishes are generally used on the a t r i u m floor to increase reflection into the side spaces.  FIGURE 15 ATRIUM FLOOR  REFLECTING PORTION OF FLOOR  49  b. W a t e r reflects as m u c h as 70 percent of light if the surface is smooth; and if the surface is rough, about 30 percent of light is reflected (Robbins, 1986,  p.750).  Although  pools of still water are also found, water used in atria is usually d y n a m i c , in the form of fountains or cascades.  Although it is used m a i n l y for traditional reasons, for actual or  symbolic refreshment, water m a y  also be used to provide a visual sparkle, pleasant  acoustical atmosphere in the case of m o v i n g water and add to the scale and depth of the space by being a surface to mirror the surrounding spaces. T h e presence of water itself affects the lighting quality.  If the surface is c a l m , as  in a pool of still water, more light would be reflected into the well and therefore, into the adjacent spaces, as compared to a fountain where the water is not still.  T h i s m a y be used  as a reflecting surface to enhance lighting levels in the well and in the occupied spaces. O n the other hand, the reflecting surface of water m a y also be a source of glare, especially if direct sunlight falls on it. c. Vegetation in the form of trees and plants are v e r y commonly seen in atria. T r e e s and plants on the floor of the atria are used to provide shade, a sense of scale, and a soft visual atmosphere.  Plants are used on terraces and along balconies. While, to ensure  their proper growth, there are the problems of providing adequate light, steady interior temperatures, right soil, watering and maintenance of plants; the v e r y presence of plants itself affects the lighting quality. Vegetation can absorb as m u c h as 75 percent of light falling on it, grass a n d earth c a n absorb upto 93 percent (Robbins, 1986, p.750). If the walls of the atria are lined with plants, there  will be less light reaching the lower levels, as there will be m a x i m u m  absorption at every stage.  If the floor of the atria has vegetation, there will be further  absorption, and the occupied spaces around the atria at the lower levels will be most affected.  A g a i n , i f used property, vegetation can be used to reduce glare, since vegetation  absorbs light.  50  PART  2  CHAPTER THREE  METHODOLOGY  T h i s chapter describes the measurement p r o g r a m and quantitative analysis of the performance characteristics of different reflective surfaces and openings for daylighting in atria.  Scale models have been used for quantitative analysis.  T h e procedure for obtaining  the r a w data for analysis under naturally overcast s k y conditions and at the location of the study has been presented.  1.0 MODEL STUDIES  T h r e e types of design tools have been used b y daylighting researchers to predict interior daylight calculations:  computational methods,  graphic techniques  and physical  scale models ( B r y a n , 1982). P h y s i c a l scale models serve as a powerful design method for daylighting analysis. "Lighting reflectance,  scales  exactly,  measurements  a n d , with  attention  paid  to geometry,  size,  made with a scale-model building will accurately  and  surface  predict the  expected daylight levels in a full sized building" (Selkowitz & Johnson, 1980).  Thus, a  daylight model that reproduces the original structure i n a smaller scale, i f tested under similar s k y conditions, will show similar results.  Millet & L o v e l a n d (1985). identify  computational methods a n d graphic techniques to be ' a n abstraction of reality', which is not so for the physical scale models.  P h y s i c a l scale models are preferable because they  'provide the opportunity for true qualitative assessment of daylight i n space a n d for  51  precise measurement  of its photometric  characteristics'.  T h i s m a y be done by visual  observation (during the course of study) or by means of video recordings or photography. The physical scale models also offer other advantages ( B r y a n , 1982): 1  even very crude models can provide accurate quantitative  information  especially when single element design comparisons are to be made. 2. P h y s i c a l scale model building is a common practice among m a n y design offices and, with slight modifications, can result in a sensitive design tool for daylighting analysis while continuing to be a n effective device for gathering spatial and volumetric information. H o w e v e r , the time involved in studies using physical models is typically longer than the time used for computational a n d graphic techniques.  sky'  a.  T h e time taken for the construction of the physical scale models.  6.  W h e n the study has to be conducted under n a t u r a l sky conditions, the  'perfect  conditions have to be awaited. On  the  other  hand, the time taken to get  graphic techniques, and mathematical  with computational  and  calculations m a y be just as time consuming, but  once acquired, permit rapid expansion and use. scale model and taking photometric  acquainted  If such is the case, building a physical  measurements  will provide equally accurate and  detailed information.  1.1 Models for practice and daylighting research Models that are typically used in architects' offices are quite different from the ones that are used for daylighting research.  T h e set of parameters to be studied for such  models and for those designed for daylighting research are different.  In practice,  models  are typically constructed to understand the scale and m a s s i n g of the design scheme. models used here are small scale reproductions of the original design.  The  T h e y are used as a  means of simulating the actual structure and the visual role is given importance.  Other  features around the m a i n structure such as trees, pavements, roads etc. are represented so as to appear as realistic as possible.  T y p i c a l l y , the aesthetic value is given importance,  whereas for daylighting studies the model is required to be functional.  Depending on the  52  w h a t is being evaluated in the daylighting research, the models m a y need to be designed for quantitative or qualitative studies. P h y s i c a l models for lighting studies have to be versatile to allow manipulation of single-element design comparisons. wide variety of design options.  A properly planned model m a y be used to evaluate a A 'modular-type' construction has been suggested  B r y a n (1982), wherein the model becomes a support structure  by  into w h i c h various wall,  ceiling and floor reflectances, window and door configurations can be inserted for testing. In the  case of a n  a t r i u m , for example,  a square  atrium may  be converted  into  a  rectangular one by inserting a cardboard along the center if it is required to model the openings or the spaces adjacent to the well.  If there are no walls along the sides of the  atria well in the original model, different types of facade conditions in the f o r m of variable sizes and shape of openings on the walls could be used.  1.1.1  Quantitative  studies  F o r quantitative studies, models for research are used to assess the performance characteristics  of certain specific elements in the model.  to duplicate the geometrj' characteristics  of the building as  well as  T h e models m u s t be constructed the reflective  of the building materials and the surrounding areas.  are of significance to model, differ depending on the project.  and  transmissive  T h e elements which  If only the shadow patterns of  the building m a s s are to be studied, it is sufficient to model only the geometry and mass of the buildings.  B u t , if the actual reflective ability of the reflecting facades of the buildings  are to be studied, the texture and reflectivity of the model should be the same as that of the actual building facades.  Hence, it is essential to first establish w h a t aspects of the  building are critical for the study so that they can be modeled accurately and those which are not so that it can be ignored.  53  1.1.2  Qualitative Models  realism  as  studies  for qualitative  compared  studies  require  to quantitative  studies.  a considerable  amount  T h e color of the  of detailing a n d  surface,  the  relative  locations of the objects in the interior, the patterns due to direct light and the possibilities of glare are some of the factors that have to be considered.  A m i r r o r placed along the  central axis of a s y m m e t r i c a l structure m a y be used to duplicate the entire space, saving time and money.  F o r quantitative studies under overcast skies, the measurements  in the  reflected p a r t of the model will be the same as that in the part that has been measured. H o w e v e r , this is not so for sunlit conditions where the inter-reflection creates considerable distortion.  1.2 Model used for the daylighting study The  model designed to study the effect of specific reflectivities and the area of  openings on the facade of the a t r i u m well, on the daylight distribution in the adjacent spaces of the a t r i a had to be constructed accurate data for analysis.  and tested in such a m a n n e r  as to provide  T h e design of the model, the materials used , the location of  the model, the procedure followed for the study, and the sky conditions under which the study is conducted are factors in the daylighting study.  T h e following section describes the  scale model in terms of the model design and construction, materials, size and scale, and measurement  1.2.1  Model  process.  design  and  construction  A five storey a t r i u m representing an office building was used, to elaborate upon a previous study b y Cole and H u i (1988). To allow sufficient flexibility for incorporating different surface reflectances and opening sizes on the wall facade of the atria, the base model had to be designed in such a m a n n e r as to allow for changes to these different elements.  54  FIGURE 16 DESIGN OF MODEL ATRIUM  ATRIUM WELL  ADJACENT SPACE  PLAN  ADJACENT SPACE ATRIUM WELL  ATRIUM WELL  Wl=1.95 SECTION A - A  SECTION B - B NOTE: WI=WELL INDEX  55  The structure of the model had to be such that these elements could be attached, removed and reused easily. Since the model was symmetrical, measurements were taken on only one side. Therefore, only the side where the measurements were to be taken was built to accommodate the adjacent space with photo cells used for recording the illumination levels. The measurements were to be taken a level at a time. Since the material of the model had to be opaque and reasonably lightweight, it was made of wood. The exterior walls were made of 12 mm ply and the floors of 6mm ply. The base model did not have any fenestration on the sides facing the atria well. Plywood was used to separate the space into levels of the required heights. This resulted in five compartments representing the adjacent office spaces on one side which did not have any reflective surface on the walls, floor and ceiling, and which were completely open on the side facing the well (refer Figure 16 and Plate 3 in Appendix B). A door, hinged on one side opening to the outside was used on the exterior face of the model so that there would be no light leaks into the model from the outside. Now, the adjacent space could be accessed from two sides at each level which was convenient for laying the photo cells at the predetermined locations. The bottom of the door on the non-hinged side had a small niche through which wires of the photo cells could be passed through when the door is shut, to avoid damaging the wires (refer Plate 4 in Appendix B). The openings on the wall facade of the atria represented windows. The size of the openings were different for the three sets of experiments. The openings did not have any glazing material. The roof over the atrium well was considered to be a simple skylight with maximum glazing. But no glazing was used on the openings of the walls or the roof. This was because, since the study was only quantitative, the penetration data could just as easily be multiplied by the transmission coefficient of any glazing types selected. The glazing materials for the openings of the wall in the model were considered have a coeffeicient of 1.0.  56  Adjacent space T h e 'office r o o m ' of the adjacent space was essentially a rectangular box open on the side facing the atria, to fit into each level in the adjacent space.  T h e box was made of  card and the sides representing the walls, floor and ceiling were made of the specified reflectivities conforming to the I E S standards, which were 85% reflectivity for the ceiling, 50% for the wall and 25% for the floor. Photo cells were to be laid on the floor of this room at specified points a n d this could slide into any level in the adjacent spaces (refer Plate 5 in A p p e n d i x B).  1.2.2  Materials A s the objective of the study was to establish the effects of different wall surfaces  on the penetration and distribution of light in the spaces adjacent to the atria, the exact reflectivity of the walls and the floor for the model a t r i u m had to be obtained. also  h a d to be light-tight to avoid a n y  light leaks,  which m a y  T h e model  cause errors  in  the  measurement.  1.2.2.1  Reflectivities It was  anticipated that lighting levels would change  drastically in the  higher  reflectance range for s m a l l decreases in the reflectivity t h a n in the lower reflectances (Cole & H u i , 1988  , C a r t w r i g h t , 1985,  O r e t s k i n , 1982).  Therefore, a range of the  was chosen with s m a l l intervals in the high reflectances  reflectances  and large intervals in the low  reflectances. T h e r e were two possibilities for obtaining surfaces of known reflectivities on the wall facade: either the surface h a d to be coated w i t h the known reflectance, or the facades had to be modeled f r o m materials of k n o w n reflectance.  P a i n t manufacturers offered only  approximate reflectance values and not the exact reflective capacity of their products.  For  the daylighting study, this information was not precise, although in reality, the exact  57  reflectivities of the materials lining the walls and the floor of existing atria m a y or m a y not be known.  Therefore, it was essential to find a material whose reflectance values were  known, a n d which could also be used for the model a t r i u m . The  only  model-making  material  that  offers  accurate  reflectivity  manufacturers under the trade name, Crescent B o a r d (Robbins, 1986, p.750-751). offered a wide range of cards of different colors and reflectivities.  is  by  They  T h e cards also fulfilled  other criteria for obtaining reliable information on the daylighting study.  T h e cards can be  easily cut with a utility knife. A range of reflectivities were selected to satisfy the conditions for the reflectances explained earlier, a n d their reflectances were rounded off for convenience. T h e y are: Arctic W h i t e (No. 3297): 91.4% reflectance, rounded to 90% Antique B u f f (No. 1095): 85.5% reflectance, rounded to 85% M i s t (No. 1088): 76.3% reflectance, rounded to 75% E x t r a L i g h t G r a y (No. 928): : 49% reflectance, rounded to 50% L i g h t G r a y (No. 923): 27% reflectance, rounded to 25% and for the study of the floor,  R a v e n B l a c k (No. 989): 6.7% reflectance, rounded to 5%.  1.2.2.2  Light-tight One of the important criteria to be met with, in choosing the material for the atria  facade w a s to ensure that it is opaque.  If the material is transparent or translucent,  unwanted light penetrates into the model. In quantitative studies, light leaks m a y not be easily discernible to the eye, however, i f present, they distort the measurements.  The  illumination m e a s u r e d at a point i n the adjacent space should be only 'wanted' light, i.e., light transmitted into the space only through the aperture i n the wall facade. such as foamboard a n d most paper products are translucent. board, h e a v y paper a n d plywood are materials that are opaque.  Materials  Chipboard, illustration  58  T h e other criteria that h a d to be satisfied was that the material should be light weight and therefore easy enough to be handled. T h e materials used for the wall facade of the atria were expected to be inserted and removed a number of times d u r i n g the course of the experimental study. Therefore, they also had to be sturdy.  1.2.3  Size and  scale  T h e size and the scale of the model h a d to be appropriately chosen so that the photo cells could be moved easily.  A l s o , as the location of the model for the  measurement  procedure was different from its location during construction, the size of the model had to be such that it could be moved with relative ease. T h e size of the a t r i u m selected in plan and section h a d to accommodate a range of well indexes.  T h e size of the a t r i u m at the selected scale h a d to be of a convenient size, so  that it could be moved relatively easily without a n y difficulties. Since the adjacent space had to be moved f r o m level to level, and with it the photo cells, a convenient working size was required to be established. 12m by 6 m . adjacent  T h e actual dimensions of the a t r i u m well i n plan were  T h e total height of the a t r i u m was 15m.  spaces  represented  a n office room,  12m  E a c h storey was 3 m high.  wide and 9 m  deep.  The  T h i s had  to  constructed to a convenient working scale. G e n e r a l l y , the level of data required for the study determines the scale of the model.  T h e governing criteria for quantitative scale model analysis is to ensure that the  the photo cells can be placed and moved with relative ease in the model. T h e scale of the model also h a d to conform with the size of the photo cells.  If the scale of the model was  too s m a l l , the photo cells would be out of scale to measure light incident on a work surface. T h e model was constructed to a scale of 1:30  (3/8"  =  l'-O").  T h e photo cells were  placed in the model at the height of the work plane (desk top height).  If the size of the cell  was v e r y large, it could affect the daylight distribution inside the model. T h e diameter and the height of the cell were the same, 0 . 0 1 8 m . T h i s , in the scale of the model was 0.6m  59  FIGURE 17 DIFFERENT ARRANGEMENTS OF PHOTO CELLS  + -r—!--!--  PHOTO CELLS  +.-T—H-r-  GRID PATTERN  LINE PATTERN  60  from the floor level. T h u s , the illumination levels recorded in the adjacent spaces were on the working plane.  1.2.4  Measurements Photometric evaluation of the model involves m e a s u r i n g illumination levels in the  space.  A number of photo cells are needed to measure illumination within the  space and outside.  adjacent  B o t h interior and exterior illumination measured simultaneously are  required to calculate daylight factors. Either different light meters, or one light meter having different photo cells could have been used.  Since the sudy was conducted under overcast conditions, illumination  levels were expected to be lower than under direct sunlight. Therefore, a light meter range of 0-10,000 lux was expected to be sufficient. A M e g a t r o n architectural model light meter was used to take the measurements.  It h a d twelve photo cells (refer Plate 6 in A p p e n d i x  B). T h e light meter was calibrated to establish differences in the sensitivity of a n y two cells.  B y calibrating, the correction factors of the cells could be determined, and cells could  be appropriately selected for placement in the modeL  T h e correction factors were used to  calculate the exact correct interior and exterior illumination before calculating the daylight factors. T h e measurements can be taken, using a single photo cell at a time, at a specific point in the adjacent space.  T h i s is not a very convenient method, as the cells have to be  constantly moved to different points to take the readings.  If however, a number of cells  are used, the readings can be taken easily taken after a r r a n g i n g them only once.  If  different cells are used, they can be arranged either in a grid pattern or in a line pattern (Robbins, 1985)  (refer Figure 17).  L i n e measurements were taken, u s i n g a series of photo  cells in a single row in the center of the adjacent space.  A line of photo cells were placed  perpendicular to the aperture, as the fall of light levels f r o m points near the atria to the  61  FIGURE 18 POSITION OF PHOTO CELLS IN THE MODEL ATRIA  B=1.8 m C=3.0 m D=5.4 m  62  back of the room was to be recorded.  T h e position of the cells was also important.  The  cells were placed at short intervals near the a t r i u m space, and further apart at the back of the room. T h i s was because, light was expected to change significantly at points near the opening. T h e decrease in the daylight factor between subsequent points near the opening was v e r y important.  H e r e , cells were placed at 0.6m and 1.2 m apart.  room, the cells were placed 2.4m  apart,  at  larger distances  as  A t the back of the  the light levels  were  expected to fall gradually, and the differences in the light levels between these points was not expected to be significant.  T h e y were placed at 0.6m,  1.8m,  3.0m,  5.4m and  7.8m  from the a t r i u m wall (refer F i g u r e 18). T o measure the exterior illumination, a photo cell was placed at the top of the model.  1.2.5  Measurement  Process  C a r d s of the predetermined reflectivities were cut to the exact dimensions of the walls and the floor of the a t r i u m well.  1.2.5.1 W a l l s The  measurement  measurements  procedure  was  carried  out  i n three  sets.  for the walls and the floor of the atria were recorded.  readings consisted of openings of 25% in the wall facade of the atria.  In  each  T h e first set of In the second set,  the size of the openings w a s 50% of the wall a r e a and in the third set it was 75%.  In each  set, readings were taken for all the five different surface reflectivities, v i z . , 90%, 75%,  50% and 25%  (refer Plate 7 in Appendix B).  set,  E a c h set of readings was  85%,  repeated  twice, and the average of these readings was calculated. T h e measurement p r o g r a m was conducted systematically, starting w i t h the highest reflectivity, and using the others in a descending order.  T h e office room containing the  63  FIGURE 19 MEASUREMENTS AT LOWER WELL INDEXES  ROOM  Wl=0.375  DOOR FLOOR WM1.17  Wl=1.95  STRUT  WALL  NOTE: WI=WELL INDEX  FIGURE 20 EFFECTS ON LIGHT DISTRIBUTION BY VARYING REFLECTIVITY ALONG PERIMETER OF FLOOR  65  photo cells at the specific points was placed on level five and readings were taken for this level, that is, well index 0.375 (level five in the model) (refer Plate 8 in A p p e n d i x B ) . T h e exterior illumination was recorded simultaneously.  A set of readings was  made for both, black and white atria floor. T h e same procedure was repeated for well index 1.17 and 1.95, i.e. at levels 3 a n d 1.  T h e office room was moved according to the level that was to be measured. T h e reflectivity of the walls w a s then changed,  a n d the entire  repeated, in the m a n n e r described above for all the well indexes.  procedure w a s  T h i s was done until the  entire set of reflectivities for the 25% opening on the w a l l was completed.  A n o t h e r set of  readings was taken for this set before the cards were used for 50% openings.  The  procedure for this set was the same as that for the 25% area of openings, except for some additional readings using the 90% reflectivity on the walls at level one.  1.2.5.2  Floor T h e effects of light distribution using white over black floor w a s done for all well  indexes and all conditions of the walls.  In addition, to establish the changes i n lighting in  the side spaces b y v a r y i n g the reflective surface of different parts of the floor, combination of white and black floors were used. Measurements  were to be taken at well indexes,  0.375 (level  three) a n d 1.95 (level one), so the floor h a d to be raised to these levels. the ground floor did not present a problem.  five),  1.17 (level  M e a s u r e m e n t s at  T w o struts h a d to be made to raise the floor,  one each for well index 0.375 and 1.17 (refer F i g u r e 19). F i r s t readings were taken u s i n g a complete black floor.  F o r the 50% openings on  the wall, additional readings at well index 1.95 were taken as follows: starting with a black floor, the reflectivity along the perimeter was increased incremently b y 25%, till the floor was completely white (refer F i g u r e 20). T h i s w a s done for well index 1.95 only.  66  The set of readings for the 75% opening on the wall followed the same procedure as that for the set of readings with 2 5 % opening, which involved using only the white and the black floors.  2.0 DAYLIGHT FACTOR  Daylight factor is defined as the ratio of interior illuminance on a horizontal surface to the exterior illuminance on a horizontal surface simultaneously available outdoors from an overcast sky. It can also be applied to clear skies, but has to take into account the variations in luminance values on the horizontal surface for altitude and azimuth. Direct sunlight is excluded for interior and exterior values of illumination. This is expressed (as a percentage) as:  Daylight Factor =  interior illuminance  x 100  exterior illuminance It is, therefore, only a relative measure of the illuminance and not the absolute measure. Daylight factor can be divided into three main components: a. Sky component. 6. External reflected component. c. Internal reflected component. The sky component is the relative illuminance striking a given point received directly from the sky. In top-lit atria, the illumination from the sky will depend on the sky vault covered by the roof. In the case of side-lit atria, the angle of the sky vault seen from a given point in the atrium well/side space is obtuse. The illumination from the sky component is greater for the top-lit atria under overcast conditions, as, the sky luminance is greater at the zenith than at the horizon.  67  T h e external reflected component is the relative illuminance striking a given point received from external reflecting surfaces, such as the facades of adjacent buildings.  The  internal reflected component is the relative illuminance striking a given point received from the daylight inter-reflected around the room. F o r the overcast sky, the external reflected component is r a r e l y more t h a n a very small fraction of the total daylight factor.  H o w e v e r , this could play a major role if the  given point in a n a t r i u m space has no direct view of the sky.  T h e internal reflected  component is the illumination at a given point due to inter-reflection f r o m the walls, floor and ceiling. "In d r y tropical regions, where the sky luminance distribution is predictable, where the  average s k y luminance remains  reflected  fairly constant  sunlight f r o m the ground and f r o m other  throughout  the  buildings makes  day,  and  a fairly  where  constant  contribution to the interior illumination the daylight in an interior can v e r y usefully be specified in terms of absolute values of illumination.  In cloudy and h u m i d climates,  the  outdoor  (Hopkinson et.  59).  illumination  varies  with the  cloud cover"  al,  1966.  p.  Therefore, in such regions daylight is variable and daylight factor gives a more meaningful expression to the interior lighting.  3.0 SKY CONDITIONS  Models for daylighting studies m a y be used under natural or artificial skies. most cases, testing outdoors under the real sky is easier and economical.  In  B u t , it is not  possible to reproduce the same measurements for every study conducted under natural sky conditions, as n a t u r a l light is everchanging.  B y contrast, readings taken under artificial  skies can be reproduced any number of times under the same set of conditions.  68  FIGURE 21 STABLE SKY CONDITIONS FOR DAYLIGHTING ANALYSIS  OVERCAST SKY  69  A l t h o u g h studies under artificial skies m a y be preferred, they do not represent the true sky conditions. Therefore, results for studies under artificial sky laboratories have to be interpreted back into reality. U n d e r n a t u r a l skies, it is difficult to interpret results for daylighting studies in v a r y i n g light conditions, hence, they are conducted only in stable light conditions. A l s o , in reality, since the building will be subjected to changes in weather, it is be more meaningful to evaluate for the extreme conditions, to ascertain the buildings full scope and range of performance. T h e clear and the overcast skies are the two extreme stable sky conditions for daylight design and the partly cloudy sky, as a condition between the two (refer F i g u r e 21). F u l l y overcast conditions obscure the sun completely (Hopkinson et. al, 1966, 46).  p.  Therefore, the illumination levels for the fully overcast sky is always lower t h a n any  other sky condition. In all regions where cloudy skies are predominant on account of high latitude, climate and industrial haze, this represents the worst case and hence studies on daylighting use this type of sky condition. T h e luminance between any two points of the sky vault of the overcast sky is not the same, although it is not as variable as that of the clear s k y . brighter  T h e distribution of luminance is s y m m e t r i c a l about the zenith, and, the sky is  at  zenith t h a n  (Commission  at  Internationale  azimuth. de  This  l'Eclairage)  is taken standard  into  consideration  overcast  sky.  for  The  the  CIE  luminance  gradually decreases a w a y from the zenith, till it reaches only a third of the zenith value at the horizon. T h e daylight factor for a particular point in the interior for the overcast sky is constant  throughout  overcast days.  the  day,  and only the  absolute  illumination varies  for different  T h u s the time of the day is not a v e r y crucial factor, as, while the absolute  illumination at a particular point varies f r o m moment to moment i n the day, the daylight factor remains constant.  F o r the study, the n a t u r a l overcast sky was used. T h e problem,  70  however, was to actually wait for the right sky condition to carry out the study. Since the proportion of the interior and exterior illumination remains the same for the overcast sky, the measurements taken for different overcast days would be valid.  4.0 LOCATION  The experimental study was conducted at the University of British Columbia, in Vancouver. The testing had to be carried out on a relatively unobstructed site. If there were obstructions such as buildings or trees around the test model, they would affect light penetration into the model which would have to be accounted for, while calculating the daylight factors. To avoid this, an open space was essential. The model was placed on the roof of a building. The location was a four level car park, and the model was placed on the roof. There were no obstructions, either from pedestrian traffic or from any buildings or trees (refer Plate 9 in Appendix B).  71  CHAPTER FOUR  RESULTS  This chapter of the thesis presents the results of the daylighting study and attendant discussion regarding the implications of surface reflectances and the size of openings on atria walls, with respect to daylight in the adjacent spaces.  1.0 DATA ANALYSIS  The methodology for the daylight measurements taken for the specific reflective surfaces and opening sizes on the wall facades have already been explained in section 1.2 of Chapter 3. The surface reflectances of the wall used are 90%, 85%, 75%, 50% and 25%, and the floor, 90% and 5% reflectivities. The facade conditions for which they have been used are 25%, 50% and 75% area of openings on the wall.  1.1 Walls  Graph 1 shows the decrease in the daylight factors in the adjacent space with distance from the atrium space. The daylight factor distribution in the adjacent space has been plotted for different surface reflectances of the walls by using a log scale.  The floor was white (90%  reflectance). Graphs 2 and 3 show the results for 50% and 75% openings of the wall facade respectively.  72  GRAPH 1 VARIATION IN DAYLIGHT FACTORS FOR 25% OPENING  10  Y  g  0.1  0.01 0  2  4  6  DISTANCE F R O M ATRIUM (m)  -I-  90% REF. 50% REF.  85% REF.  °  - S - 25% REF.  AT W E L L INDEX 1.95  75% REF.  8  73  GRAPH 2 VARIATION IN DAYLIGHT FACTORS FOR 50% OPENING  10  0.1 H 0  1  1  1  2  4  6  DISTANCE F R O M ATRIUM (m)  -I—  90% REF.  85% REF.  *-  50% REF.  - 0 - 25% REF.  AT W E L L INDEX 1.95  Q  75% REF.  1  8  GRAPH 3 VARIATION IN DAYLIGHT FACTORS FOR 75% OPENING  0  2  1  r  4  6  DISTANCE F R O M ATRIUM (m)  —r-  90% REF. 50% REF.  "*  85% REF. 25% REF.  AT W E L L I N D E X 1.95  Q  75% REF.  8  75  T h e following observations can be stated: a.  Higher the wall surface reflectance, higher is the daylight  factor.  A l l graphs exhibit a similar curve: the higher the reflectance of the a t r i u m wall, the greater is the daylight factor in the adjacent space. If the surface reflectivity of the walls is high, available light in the well due to inter-reflection also increases. to atria.  T h i s provides higher daylight factors in the spaces adjacent  T h e daylight factors at locations at the back of the room (at 5.4m a n d 7.8m), for  the three different wall facade conditions are less dependent on the surface reflectivities of the wall.  T h e daylight factors lie between 0.56 and 0.1.  b.  Daylight  factor decreases significantly  between two consecutive points at  small  distances from the well. T h i s is especially the case w i t h lower well index of atria.  A s distance f r o m the  atria well increases, the differences in the daylight factors between these points become less significant. A t points near the a t r i u m well, the difference in the daylight factor between two points for a given reflectance successively decreases with increase in the a r e a of opening. B u t daylight factors for specific points in atria of higher well index are not significantly enhanced u s i n g a higher surface reflectance on the w a l l as in 25% opening on the wall facade.  U s i n g different surface reflectances on the wall facade to enhance reflection at the  lower levels makes significant differences only when small openings on the wall facade are used (below 25%  opening).  A s the surface  area available for reflection increases,  the  daylight factors also increase. A t points near  the opening, the daylight factors are higher due to light being  projected directly f r o m the sky vault and part due to inter-reflection f r o m the walls of the atria.  A t lower levels of atria w i t h high well indexes, the contribution f r o m the sky  component is m i n i m a l , a n d most of it is due to inter-reflection from the walls and the floor of the atria.  W i t h subsequent inter-reflections, part of the light is reflected, and p a r t  76  absorbed. levels.  T h u s , light projected at a point due to multiple reflections has lower illumination  A s a result, daylight factors are higher in the adjacent spaces at lower well index  and near the a t r i u m well, than at similar points in atria of higher well index, and for locations at the back of spaces adjacent to atria. c.  The differences in daylight  factor between any two points in the adjacent space  (near the atria well) is greater when the wall reflectivity is higher. Generally, the decrease in the daylight factors between any two points for higher surface reflectances (90%,  85%, 75% reflectance) is greater as compared to the decrease in  the daylight factors in the lower surface reflectances (50%, same two points.  25% reflectance) between the  T h e difference in the daylight factor between, say, 0.6m and 1.8m for  90% wall reflectance is more t h a n the difference between the same two points for which is, in t u r n , more t h a n that of the same points for 25%  85%,  reflectance.  H i g h e r reflectance of the wall facade gives greater daylight factors as it has been explained in 1.1 (a).  A s lighting due to inter-reflections increases towards the back of the  adjacent space, lighting becomes more uniform. W i t h regard to opening sizes on the wall, for a given reflectivity, larger the a r e a of openings (75% and 50% openings), lesser is the surface a r e a available for inter-reflections. A t a given point the daylight factor is m a i n l y due to direct rather t h a n inter-reflected light, giving therefore, higher daylight factors in the adjacent spaces, t h a n when the openings on the wall facades  are  smaller (as in 25%  openings).  Therefore, differences in daylight  factors for points near the a t r i u m well for large openings on the wall facade are significant than for s m a l l openings. d.  The  difference  in the daylight  factor  between two reflectivities in  the  higher  reflectances at any point in the side space is greater than in the lower reflectances. At points close to the a t r i u m well, (0.6m, factors in the  higher reflective range,  (90%  1.8m)  - 85%,  the difference in the daylight  85%  - 75%  a n d 75%  - 50%)  is  comparatively greater t h a n the difference in the daylight factor between these points in  77  the lower reflectances (50% - 25%).  For points at the back of the adjacent space, these  differences are very small, and insignificant. The size of the openings affect the surface area available for reflection. But, for any given area of openings on the wall, the available light will be low if the surface reflectance of the walls itself are low. As the surface reflectance decreases, the daylight factors, and hence the available light decreases. e.  The  differences  in daylight  openings on the wall facade are  factors between two reflectances are greater if the  smaller.  The difference in the daylight factor between two surface reflectances of the wall decreases as the openings on the wall facade increases.  These differences are lower for  large openings as compared to smaller openings, where they are significant. This is because the wall surface available for inter-reflecting light down the atria well is greater when the openings in the wall are smaller.  For the largest area of  openings, in this case, 75%, the wall areas have been considerably reduced, hence the difference in the daylight factors are not as significant as they are for the 50% or 25% openings of the wall facade.  1.2 Floor The readings of the illumination levels for the floor have been divided into two parts.  In the first set of readings, the reflectance of the entire floor was changed from  90% to 5% reflectance.  In the other set, to determine the parts of the floor which are  essential for increasing the daylight factors in the adjacent spaces, the perimeter area of the floor was increased incremently by 25% (of the floor area) from 0-100%, that is, from a black floor to a completely white floor.  78  GRAPH 4 DAYLIGHT FACTOR AND WALL REFLECTIVITY AT 3.0 M AND WELL INDEX 1.95  0  r  i  20 + " 75%W 75%B  -  40  80  60  WALL R E F L E C T I V I T Y  50%W 50%B  --B-  25%W 25%B  FOR W H I T E ( W - 9 0 % R E F L E C T A N C E ) A N D BLACK (B- 5% REFLECTANCE) F L O O R S FOR 2 5 % , 5 0 % A N D 7 5 % O P E N I N G S OF WALL  100  79  1.2.1  Entire  floor  T o understand the influence of the floor reflectivity on the illumination levels of the adjacent spaces, white (90%  reflectance) and black (5% reflectance) floors, were used for  the three different facade conditions. T h e daylight factor at a point 3.0m from the a t r i u m well was plotted against the wall reflectance for each condition.  G r a p h 4 shows the relationship between the daylight  factors and the surface reflectivity of the wall for well index 1.95,  for the three conditions  using the white a n d the black floor. T h e following points can be observed: a.  Using a floor of 90% reflectance in the atrium well increases daylight  factors.  T h e difference in the daylight factors using the black and the white floor at well index 1.95 shows that the daylight factor in the adjacent space is significantly higher when the floor reflectivity is also high (refer G r a p h 4) for a n y size of openings on the wall facade.  T h e daylight factors could be increased upto five times the original values (using  black floor). W i t h regard  to the reflectivity of the wall facade,  the difference between  the  daylight factors for the white and the black floors at well index 1.95  is least for higher  reflectance (90%), a n d increases gradually upto 25% wall reflectance.  T h e increases for  90%  wall reflectance are  about 2.5  times the values (using the black floor), gradually  increasing to about 4.5 times for 25% wall reflectance. T h i s shows that when lower reflectances are used on the walls, using a higher reflectance on the floor will enhance illumination in the spaces adjacent to the atria.  Direct  reflection off the floor projects light into the adjacent side spaces, creating higher daylight levels.  Also, since the floor reflectivity is high, there is m a x i m u m inter-reflection between  the wall and the floor, thereby increasing the daylight factors.  GRAPH 5 DAYLIGHT FACTOR AND WALL REFLECTIVITY AT 3.0 M AND WELL INDEX 0.375  20  40  60  80  WALL R E F L E C T I V I T Y  75%W 50%B  50%W 0-  25%W  -a-  75%B 25%B  FOR W H I T E ( W - 9 0 % R E F L E C T A N C E ) A N D B L A C K ( B - 5% R E F L E C T A N C E ) F L O O R S FOR 2 5 % , 5 0 % AND 7 5 % O P E N I N G S OF WALL  100  81  b.  There are no significant  changes in the daylight  factors in the side spaces for  openings beyond 50% openings on the wall facade. A t well index 1.95 there is very little difference in the daylight factors between the 50% and 75% openings on the wall facade, for either the white or the black floor (refer G r a p h 4). G r a p h 5 shows the relationship between daylight factor and surface reflectance of the wall for well index 0.375. A t well index 0.375 the difference in the daylight factor for both, white and black floors is not v e r y significant with increase i n the openings on the w a l l facade. factors using smaller openings (25%) larger openings (50% and 75%)  T h e daylight  on the walls w i t h a white floor can be compared to  with black floor.  T h e daylight factors lie between 3.0 and  5.0. In general, the differences in the daylight factors between 50% openings a n d  75%  openings on the wall facade can be neglected when compared with 25% opening on the wall facade. and  If the a r e a of the openings on the wall facade were to lie anywhere between  50%  75% or more, the increase in the daylight factors beyond the present values of 50%  and 75% openings of the wall facade would almost be negligible. H o w e v e r , if the openings on the wall facade were to decrease lower than 50%, upto 25% or even less, the daylight factors of these new openings on the wall facade will correspond with the present values of 50% and 25% areas of the wall openings which is appreciable. walls are reduced below 25%,  W h e n the openings in the  the daylight factors will be even lower.  the daylight factors using smaller openings in the  T h e differences in  walls, when decreased  below  25%  opening on the wall facade is significant. Alternatively, if the increase in the area of openings in the wall is f r o m 0-50%, the increase in the daylight factors with increase in the a r e a of opening at every step would be substantial.  If the openings on the walls are larger, beyond 50% of its area, the increase  82  GRAPH 6 DAYLIGHT FACTOR AND WALL REFLECTIVITY FOR 25% OPENINGS AT 3.0 M  5  AT W E L L INDEX 0 . 3 7 5 A N D 1.95 FOR W H I T E ( W - 9 0 % R E F L E C T A N C E ) A N D B L A C K ( B - 5% REFLECTANCE) FLOORS  83  GRAPH 7 DAYLIGHT FACTOR AND WALL REFLECTIVITY FOR 50% OPENINGS AT 3.0 M  8  J--'""  + +  6 D A Y L I G H T F A C T O R  +  +  4  2 -  x  0  0  20  —  ^ 40  60  80  100  WALL R E F L E C T I V I T Y  •+•• 0.375W  0.375B  -e- 1.95W  AT W E L L INDEX 0.375 AND 1.95 FOR W H I T E ( W - 9 0 % R E F L E C T A N C E ) A N D B L A C K ( B - 5% R E F L E C T A N C E ) F L O O R S  1.95B  GRAPH 8 DAYLIGHT FACTOR AND WALL REFELCTIVITY AT 3.0 M FOR 75% OPENINGS  20  40  60  80  100  WALL R E F L E C T I V I T Y  0.375W  - * - 0.375B  - B - 1.95W  1.95B  AT W E L L INDEX 0.375 A N D 1.95 FOR W H I T E ( W - 9 0 % R E F L E C T A N C E ) A N D B L A C K ( B - 5% R E F L E C T A N C E ) F L O O R S  85  in the daylight factors for a n y surface reflectance of the wall is not significant. because with larger openings on the walls, the area for reflection is reduced.  T h i s is  T h i s is more  so i n well index 1.95 than i n well index 0.375, as, at well index 1.95 lighting is m a i n l y dependent on inter-reflection as compared to the shallow well in well index 0.375. c. Difference in the daylight factor between 90% reflectance and 5% reflectance of the floor for any area of opening of the wall is higher in well index 0.375. G r a p h s 6, 7 a n d 8 show the relationship between the daylight factor a n d the reflectivity for the well indexes 1.95 and 0.375, using the white and the black floors for 25%, 50% and 75% openings of the wall facade. T h e differences in the daylight factors between white and black floors for different wall reflectances is higher i n well index 0.375, than in well index 1.95.  T h i s is for a n y  opening sizes of the w a l l facade. T h e differences are higher for the low well index because the points in the adjacent spaces are less dependent on the facade condition or surface reflectance of the wall facade than for similar points in lower levels at higher well index.  T h e high daylight factors are  for the most part directly f r o m the sky vault. T h e increase  i n the daylight factor between well index 1.95 a n d 0.375 for a n y  condition i n the openings of the wall using either the white or the black floor is more for the 25% wall reflectance than for the 90% wall reflectance.  T h i s is because at the upper  levels a major part of the daylight factor is due to the contribution f r o m the direct sky component and v e r y little due to inter-reflections.  T h e illumination levels decrease rapidly  for the 25% wall reflectance towards the lower levels on account of lower reflectivity of the wall.  U s i n g black floors, the reflectivity is further reduced, hence the daylight factor in the  upper levels has a significant increase for the 25% reflectance of the wall surface. d. The difference in daylight factor between well index 1.95 and 0.375 is significant for larger openings of the wall facade.  GRAPH 9 FOR VARIOUS OPENINGS USING WHITE FLOOR AT 3.0 M  +  1  1  1  1  •  40  60  80  100  i  0  20  WALL R E F L E C T I V I T Y  +  75%-0.375 75%-1.95  *  50%-0.375 50%-1.95  •  25%-0.375 25%-1.95  AT W E L L INDEX 0 . 3 7 5 A N D 1.95 FOR 2 5 % , 5 0 % A N D 7 5 % O P E N I N G S OF WALL  87  G R A P H 10 FOR VARIOUS OPENINGS USING BLACK FLOOR AT 3.0M  20  0  40  80  60  WALL R E F L E C T I V I T Y  "l— x  25%-0.375  75%-0.375  *  50%-0.375  -B-  75%-1.95  0  50%-1.95  -A- 25%-1.95  AT W E L L I N D E X 0 . 3 7 5 A N D 1.95 25%, 5 0 % A N D 7 5 % O P E N I N G S OF WALL  100  88  G r a p h s 9 a n d 10 are plotted at 3.0 m from the opening for the white and black floor.  T h e curves  have been d r a w n for different openings of the wall facade at well  indexes 1.95 and 0.375. T h e increase i n the daylight factor for the white floor from well index 1.95 to well index 0.375 for different surface reflectances at points 3 . 0 m from the a t r i u m well in the adjacent space is greater when the openings on the wall facades are larger (refer G r a p h 9). F o r the 25% openings, the increase i n the daylight factor w a s from 2 times the values at well  index  reflectance.  1.95  for 90% reflectance  upto  5 times  increase  in the values  for 25%  T h e daylight factors using white floor at well index 0.375 was enhanced as  the surface reflectance of the wall decreased. F o r large openings (50% and 75%) on the wall facade, the increase w a s from 3 times for 90% reflectance in well index 1.95 to 6.5 times for 25% of the wall reflectance. F o r the black floors, (refer G r a p h 10), the same pattern followed. F o r the 50% and 75% openings on the wall facade, the increases were upto 9 times the values at well index 1.95 for the 90% wall reflectivitj , while the values increased b y as m u c h as 25 times for 7  25%  wall reflectivity.  F o r the 25% openings, the increase  was 4 times for 90% wall  reflectivity and 12 times for the 25% wall reflectivity. O w i n g to the comparatively large a r e a of surface reflectance for the 25% openings on the wall facade, the distribution of light down the well and in the side spaces is u n i f o r m . B u t , for the 50% a n d 75% openings on the wall facade the differences between the well indexes are critical.  1.2.2  Specific  parts  of the  floor  T o establish which part of the floor a r e a enhances reflection, the reflectance along the perimeter of the floor was increased.  It was hypothesized that the a r e a along the edge  of the floor plays a k e y role i n the lighting of the spaces adjacent to it. Direct reflection into the adjacent spaces, and further inter-reflection into locations remote f r o m the atria  89  G R A P H 11 DAYLIGHT FACTORS FOR SPECIFIC PARTS OF THE FLOOR (ALONG PERIMETER)  5  0 BLACK  20  40  60  80  A R E A O F T H E R E F L E C T I N G S T R I P {%)  AT 0 . 6 M  *  AT 3.0M  AT W E L L INDEX 1.95 FOR 5 0 % O P E N I N G S OF WALL  100 WHITE  AT 7.8M  90  well projects light into the side spaces.  If the reflectance of this area of the floor is  increased, the daylight factors were expected to increase significantly. F o r only 50% openings of the wall facade, starting with a black floor, the area of reflectance along the perimeter of the floor was increased in increments of 25%,  till the  floor was completely white. G r a p h 11 is plotted for well index 1.95, floor surfaces available for reflection.  u s i n g daylight factor against area of the  T h e graph has three lines, one showing the increase  in the daylight factor at 0.6m f r o m the opening, another at 3.0m f r o m the opening and the third at 7.8m from the opening. T h e following observations can be stated: a. Increasing  the floor reflectance increases the daylight  factors.  W h e n the surface reflectance along the edge of the floor is increased, the daylight factor in the adjacent space increases.  T h e daylight factors are higher at distances close to  the opening on the wall facade than at points at the back of the adjacent space. L i g h t reflected off the floor edges is projected into the side spaces, directly or for further reflection, unlike the core where light m a y be reflected partly into the a t r i u m well and partly into the side spaces.  Hence, increasing the reflectivity along the edges of the  floor increases the daylight factors in the lower levels. b.  For  50%  openings  on the wall facades  of the atria,  the daylight  levels were  enhanced only if the area of the perimeter reflectance is greater than 25% of the floor area. A s shown in g r a p h 11, the increase in the daylight levels between 0-25%  in the  reflecting strip along the perimeter of the floor is not proportional to the increase in the light levels beyond 25% of the a r e a of the reflecting strip. Since the openings are 50% of the wall a r e a (and placed along the center of the wall), part of the wall below the opening acts as a n obstruction to the light reflected off the perimeter of the floor.  P a r t of the light projected off the perimeter enters the adjacent  space through the opening a n d p a r t of it is bounced back into the a t r i u m space.  However,  for increments beyond 25% of the floor along the perimeter, light reflected off this zone is  91  projected into the side spaces. strip is larger,  T h i s is because light projected off the area of the reflecting  compared to the light reflected back into the  obstructing wall below the opening.  a t r i u m well due to  the  Locations along the back of the a t r i u m space are not  affected by changes in the reflectivity of the perimeter of the floor, as lighting at these points is more or less u n i f o r m . It is quite possible that the area of the perimeter of high reflectance of the floor m a y be equivalent or greater than the area of the wall below the opening on the wall surface.  Therefore, for the 50% area of openings on the wall, the a r e a of reflection of the  perimeter of the floor is less than that of the 25% openings.  A n d , for the 75% openings of  the wall, the perimeter area would be even less than that of the 50% openings.  T h i s is  because the obstructing wall below the opening is smaller for the 50% and 75% openings of the walls.  T h u s , location of the opening and its size determines  the part of the floor  perimeter that is needed to enhance the illumination in the adjacent spaces.  It is also  possible that the a r e a of the reflecting strip is proportional to the height of the wall below the opening. c.  The increase in the daylight factors with increments along the perimeter of the floor  is not consistent at specific points in the spaces adjacent to atria. T h e differences in the daylight factors between 0 . 6 m - 3 . 0 m , and 3 . 0 m - 7 . 8 m become significant as the a r e a of reflectivity along the edge of the floor increases. when the floor is black and highest when the floor is white.  It is the least  A l t h o u g h , the daylight factors  generally increased w i t h increase in the floor reflectivity, the percentage increase at these points in the adjacent space were not the same.  T h e values were 3.13  to 4.7 for  0.6m  f r o m the opening, 0.41 to 1.45 at 3.0m f r o m the opening, and 0.1 to 0.27 at 7.8m from the opening. T h e reason for the inconsistency in the increase m a y be due to very low values in the daylight factor at the back of the rooms.  Hence, the increases in the daylight levels at  locations at the back of the rooms become insignificant.  G R A P H 12 DAYLIGHT FACTORS AND WELL INDEX AT 3.0 M  * • x \  _l  !  !  j  0  0.5  1  1.5  W E L L INDEX +  75%W  50%W  x  75%G  50%G  - B -  25%W 25%G  FOR 90%(W) AND 25%(G) WALL R E F L E C T I V I T Y FOR 2 5 % , 5 0 % A N D 7 5 % O P E N I N G S OF WALL  2  93  1.3 Well Index G r a p h 12 presents the relationship between daylight factors and well index using 90% and 25% surface reflectance a n d 90% floor reflectance, for conditions 25%, 50% and 75% of the openings of the wall. Irrespective of the surface reflectance, points, decrease as the well index increase.  the daylight factors measured at specific  F o r all curves, the differences between the  well indexes were greater between well index 0.375 a n d 1.17 as compared to the difference between well index 1.17 a n d 1.95.  T h e differences in the daylight factors between 90%  and 25% surface reflectance of the wall at well index 0.375 was greater than at 1.95, for 50% and 75% openings of the wall facade. the graph shows a different relationship.  H o w e v e r , for 25% openings on the wall facade, H e r e , the differences in the daylight factors  between the surface reflectances at the two well indexes were comparable. T h e reason for a more uniform distribution of light for the 90% reflectance curve for 25% openings on the wall facade derives from the increased inter-reflectance of light down the well, a n d hence into the side spaces.  A s the a r e a of openings are smaller here  t h a n for the other two conditions of the wall facade, there is m a x i m u m inter-reflection of light.  In addition, most of the light is inter-reflected a n d v e r y little is absorbed, owing to  the high reflectance of the wall facade.  Therefore, the light projected into the adjacent  spaces at the lower levels is m a i n l y inter-reflected light.  F o r either surface reflectance of  the wall, the distribution of light in the spaces adjacent to the well is more uniform for the 25% opening t h a n for a n y other area of opening of the wall facade.  2.0 DESIGN IMPLICATIONS  Section 1.0 discussed the results using daylight factors as a means of expressing the illumination levels at given points i n the spaces adjacent to the atria. the illumination levels are expressed i n terms of lux.  In this section,  U s i n g the daylight factors already  94  calculated from the raw data, and the exterior illumination of an overcast sky to be an average of 7,500 lux (normal overcast sky varies from 5,000-10,000 lux), the interior illumination values were calculated. These are therefore the estimated values, and not the actual values, for the atrium based under the following assumptions (already given in chapter 3): 1. The roof covering the atrium well is a simple skylight with maximum glass area. The light levels in an atrium well are dependent on the transmission characteristics of the glazing material of the roof. In this case, the glazing coefficient of the roof was considered to be 1.0, so no light is reflected or absorbed by the roof glazing. All the light is transmitted down the well, so this atrium functions as a light well. 2.  Similarly, the glazing material on the opening of the wall facades  was  considered to have a transmission coefficient of 1.0, so light transmitted through these openings are projected directly into the side spaces, without any part being reflected or absorbed. 3. The different opening sizes of the wall facade are located in the center of the wall at each storey. 4. The illumination levels given are at the working plane in the side spaces of the atrium, i.e. at 0.6m from the floor and, at points 0.6m, 1.8m, 3.0m, 5.4m and 7.8m from the atrium well. 5.  The reflectivity of the walls, floor and ceiling of the office space has been  derived from IES Standards: 50% refelctivity of wall, 85% for the ceiling and 25% for the floor. 6. The spaces around the atria well derive light only from the atrium and not through the external walls. The contribution from the external walls will depend on factors such as orientation, size and location of the openings on these walls. 7. The proportions of the atrium remains unchanged in plan. The height of the atrium well varies, giving different well indexes.  95  G R A P H 13 VARIATION IN ILLUMINATION USING 90% FLOOR REFLECTIVITY  ILLUMINATION (lux)  0.6  1.8  3  4.2  5.4  6.6  7.8  9  DISTANCE F R O M ATRIUM W E L L (m)  AT W E L L INDEX 1.95 FOR 7 5 % O P E N I N G S  R E F L E C T I V I T Y  96  G R A P H 14 VARIATION IN ILLUMINATION USING 5% FLOOR REFLECTIVITY  ILLUMINATION (lux)  0.6  1.8  3  4.2  5.4  6.6  7.8  9  DISTANCE F R O M ATRIUM W E L L (m)  AT W E L L INDEX 1.95 FOR 7 5 % O P E N I N G OF WALL  R E F L E C T I V I T Y  97  While graphs 1-12 graphs 13-17  give a general understanding of the range of daylight factors,  deal with actual illumination values in terms of lux that m a y be achieved  under the given set of conditions.  Since lighting levels are more critical in atria of higher  well index, graphs have been plotted at well index 1.95,  unless otherwise specified.  U s u a l l y , the barrier between the adjacent spaces and the a t r i u m well is glazed. T h i s is preferred for lighting as well as aesthetic reasons.  In comparision to the total wall  area, windows and such similar openings on the atria wall facade equal 75%  or more,  being a more realistic value than 25% opening size. 1.  G r a p h 13 has been plotted for 75% openings on the wall facade.  reflectance is 90%, given circumstances. for  different  T h e floor  which will represent the m a x i m u m values of illumination under the T h e distribution of light in the adjacent office space has been shown  reflective  surfaces  of  the  wall  (refer  Graph  13).  A  maximum  of  approximately 350 lux m a y be achieved at a point 0.6m f r o m the a t r i u m well for 90% wall reflectivity a n d 270 values  lie between  lux for 25% wall reflectivity. 12  lux  and  24  lux.  A t 7.8m from the a t r i u m well, these  Clearly,  these  points  will  have  to  have  supplementary lighting. 2.  G r a p h 14 is a similar to graph 13, but here the floor reflectivity is only 5%.  T h i s g r a p h contains a range of illumination values when there is m a x i m u m absorption of light by the floor: hence this represents the worst case (refer G r a p h 14).  T h e illumination  at 0.6m f r o m the a t r i u m well m a y range between 190 lux and 50 lux, and at 7.8m f r o m the openings on the wall 6 lux to 2 lux.  Therefore, here also supplementary lighting will  have to be provided. 3.  Realistically, the wall reflectivity is usually not more than  facade walls around a t r i u m spaces are smooth a n d colored white. uncommon to see atria floor of high surface reflectance,  v e r y few  S i m i l a r l y , it is highly  as they usually have furniture,  plantations, etc which will reduce the overall floor reflectance. reflectivity of 75% is to be expected.  75%:  T y p i c a l l y , a m a x i m u m floor  98  G R A P H 15 VARIATION IN ILLUMINATION AT DIFFERENT LEVELS FOR WELL INDEX 1.95  ILLUMINATION (lux)  0.6 1.8 3 4.2 5.4 6.6 7.8 9 DISTANCE F R O M ATRIUM W E L L (m)  FOR 75% OPENINGS OF WALL LEVEL 1 WITH 75% REF. FLOOR, LEVELS 3 & 5 WITH 5% REF. FLOOR  99  G R A P H 16 VARIATION IN ILLUMINATION FOR CHANGES IN REFLECTIVITY ALONG PERIMETER OF FLOOR  ILLUMINATION (lux)  0.6  1.8  3.0  4.2  5.4  6.6  7.8  9  DISTANCE F R O M ATRIUM W E L L (m)  AT W E L L INDEX 1.95 FOR 5 0 % O P E N I N G S OF WALL  R E F L E C T I V I T Y  (%)  100  T h i s , therefore projects a more practical situation, with the opening sizes on the walls as 75% of the wall area, the floor and the walls with a m a x i m u m reflectivity of 75%. T h e illumination i n G r a p h 15 presents a n estimate of the actual values at different levels in side spaces of a n a t r i u m of well index 1.95. In G r a p h 15, the variations i n the illumination values have been shown at different levels for a well index  1.95.  Surface  reflectivity of the wall is 75%.  reflectance of the floor at the lowest level is 75%.  T h e surface  F o r levels 5 and 3, the lux was  calculated using 5% reflectance of the floor for well indexes 0.375 a n d 1.17.  T h i s is the  same as taking readings at these levels in well index 1.95, as light penetrating into levels lower than five a n d three respectively are i n fact 'absorbed' into the lower levels. T h e r e are large variations in the illumination at specific points i n the adjacent spaces at different levels (refer G r a p h 15).  A t level 5, the illumination at 0 . 6 m is 2400  lux, a very high value as light at this point is m a i n l y due to the s k y component.  A t the  same point i n level 3, the illumination is 910 lux, which although lower than at level 5, is still greater than at the same point i n level 1, as it still sees a part of the s k y vault. the same point at level 1, the illumination was 310 lux.  At  T h e illumination is greatly  reduced at 7.8m f r o m the atrium well, it is 43 lux at level 5, 18 lux at level 3 and 14 lux at level 1.  A comparatively uniform distribution of illumination at level 1 i n the adjacent  spaces is due to additional inter-reflection off the floor. 4.  G r a p h 16 shows the changes in the illumination values for variations in the  area of reflectivity along the perimeter of the floor (refer G r a p h 16). T h e opening sizes on the walls are 50%.  T h e changes in the lux at 0 . 6 m from the a t r i u m well varies from 230  lux (for the black floor) to 350 lux (for the white floor) a n d at 7.8m f r o m the opening, it ranges between  7 lux and 19 lux.  Increasing  the reflectivity of the floor to enhance  illumination i n the side spaces does not cause a n y significant increases i n the values at the back of the adjacent spaces. T h e changes are significant only at very small distances from the a t r i u m well.  101  G R A P H 17 ILLUMINATION AND WELL INDEX AT 3.0 M  ILLUMINATION (lux)  75%W 50%W  0.375  1.17  1.95  OPENING  SIZES  W E L L INDEX F O R 90%(W) A N D 25%(G) WALL R E F L E C T I V I T Y FOR 2 5 % , 5 0 % A N D 7 5 % O P E N I N G S O F WALL  102  The  variations between subsequent increases of the floor reflectivity along the  perimeter is dependent on the location a n d size of opening on the adjacent walls.  In this  case, the increase i n the illumination between the u n i f o r m black (0) a n d 25% area of the floor reflectivity  w a s only  15 lux.  Subsequent increases ranged  over  30 lux.  The  differences are, again significant only at small distances from the well. 5.  Graph  17 deals with the well index a n d the illumination levels for specific  reflectivities of the wall facades.  F o r each opening size, n a m e l y , 25%, 50% and 75%,  illumination values at 3.0 m f r o m the atrium well for different well indexes have been shown for the m a x i m u m - 90% reflectance and m i n i m u m - 25% reflectance of the wall facades (refer G r a p h 17).  T h i s g r a p h gives a range of values, however, based on earlier  discussions (in 3 above),  using 75% opening size on the walls, lighting levels m a y lie  anywhere between 480 and 590 lux at well index 0.375, between 220 a n d 136 lux at well index 1.17 a n d between 110 a n d 60 lux at well index 1.95. If the opening size of the walls are smaller; for the 50% openings, the illumination will lie between 450 and 480 lux at well index 0.375, between 120 and 210 lux at well index 1.17 and between 60 a n d 110 lux at 1.95. If the opening size of the walls are 25%, the illumination will lie between 210 a n d 300 lux at well index 0.375, between 75 and 180 lux at well index 1.17 and between 30 and 90 lux at 1.95.  2.1 Discussion A range of m a x i m u m , m i n i m u m a n d optimum values that would typically arise out of the given dimensions in plan a n d well index of the atria have been presented.  These  values are based on certain assumptions that have already been stated, a n d are to be merely used as guidelines i n determining the suitability of specific reflectivities on the walls a n d floor surfaces of the atria a n d for specific opening sizes on the walls of the atria. F o r atria with 75% openings, a m a x i m u m of 350 lux c a n be obtained at a well index of  103  1.95.  B u t this is for a point close to the a t r i u m well, w h e n the surface reflectivity of the  wall and the floor is 90%.  For  similar conditions, using 5%  m a x i m u m illumination is only 190 lux.  reflectivity  of floor,  A s s u m i n g the reflectivity of a t r i a floor to be  in reality, the estimated illumination values at this point will be approximately  310  which is less t h a n 350 lux, the required illumination value at the w o r k i n g plane. distance f r o m  the  atrium  well increases,  the  illumination values  decrease considerably, well below the required levels.  in the  the 75% lux,  A s the  office  space  A n d so, supplementary lighting is  required to be provided. D a y l i g h t m a y be projected into the space through windows on the external walls or by using artificial lighting. P r o v i d i n g windows on the external walls will enhance the illumination values at distances remote from the a t r i u m well, giving further reductions in the cost of lighting energy. Generally,  increasing  the  However, problems of glare cannot be ruled out.  a r e a of reflectivity  along the  perimeter  of the  floor  increases the illumination at points close to the well but the increases at the back of the space  are  insignificant.  illumination was 350 lux.  For  50%  opening  on  the  walls,  only 14  lux.  maximum  attainable  If an area of 50% along the peimeter was lined with a surface  of high reflectance, the illumination levels at 0.6m were 290 7.8m,  the  T h i s is below the  required ambient  lux, at 3.0m  52 lux and at  lighing conditions.  It would  therefore, be advisable to keep the edges of the floor free from vegetation and furniture which will act as light absorbers, and use this a r e a along the edges for circulation.  Since  water can be used for reflecting light, pools m a y be designed around a circulation core. H e r e again, glare due to high reflective surfaces is a problem to be dealt with. Irrespective of the surface reflectances of the wall, large openings on the wall facade give a wider range of illumination values.  F o r smaller openings of the wall facade,  the differences in the illumination between two well indexes are not v e r y significant. in reality,  it is very  uncommon to  find  atria with 25%  Also,  openings on the wall facade.  T y p i c a l l y , the openings in the walls are at least 75%, which covers a range of 480-590 lux  104  at well index 0.375, 120-200 lux at well index 1.17 a n d 60-100 lux at 1.95, all measured at 3 . 0 m from the a t r i u m well at the adjacent office space. H o w e v e r , the wall reflectivity is rarely  90% a n d the well index 0.375, which  ultimately gives projected illumination levels between 85-135 lux which is less than the required levels of 350 lux. Therefore, at these points supplementary lighting will have to be provided. Large  openings  provide  uniform distribution of light.  greater  illumination a n d smaller  openings  provide  a  A t levels close to the source of light i n top-lit atria, s m a l l  openings in the wall facade will provide sufficient illumination at the working plane, as light projected at points in spaces adjacent to the atria is directly f r o m the s k y vault. Towards  the lower  illumination values. increasing in size till  levels,  larger  openings  on the wall facade  will  provide  higher  Hence, it is preferrable to have s m a l l openings at the upper levels 100% openings are provided at the lower levels.  T h i s will  also  provide sufficient area for inter-reflecting light to the adjacent spaces in the lower levels of atria. To control glare, blinds a n d such similar devices m a y be used i n atria.  They m a y  perform a dual role of controlling noise levels in atria also if the materials of which they are made are good for sound absorption. S i m a i l a r l y h a n g i n g elements in atria wells m a y be used for sound absorption a n d reflection.  T h i s m a y be so provided the materials they are of which they are made are  light colored so that it reflects light.  Other elements such as m u r a l s , sculptures, etc m a y  also function as light/sound/glare controllers, i f their design, materials of construction a n d location are predetermined.  105  CONCLUSION  T h i s research set out to establish the changes i n the illumination levels in the spaces adjacent to atria resulting f r o m changes in the wall a n d the floor a n d variations i n the a r e a of the opening sizes i n the wall facade of a n atria well. conducted  earlier  hypothesized that adjacent spaces.  b y Oretskin  (1982),  C a r t w r i g h t (1985)  B a s e d on research  a n d Cole  (1988),  it w a s  changes in the reflectivity can dramatically affect the daylight in  A l s o , the changes would be significant i n the occupied adjacent spaces at  the lower levels of atria. A general conclusion is that lower the well index, greater is the illumination at that level, within the well or in the space adjacent to it. T h i s was reported b y Oretskin (1982), C a r t w r i g h t (1985) and Cole (1988).  A t a particular well index, higher reflectances on the  wall facade increases the illumination levels appreciably within the well. to spaces adjacent to the atria.  T h e same applies  H o w e v e r , the amount b y which the daylight factors  increase depends on the surface reflectance of the wall, the distance of the point from the opening i n the adjacent space and the a r e a of openings on the wall facade. F o r atria of same well index, there are considerable differences in the amount of available light depending on the surface reflectance of the walls a n d the floor.  Since  lighting i n the spaces adjacent are dependent on the a m o u n t of illumination i n the well, it is critical that the surface reflectance of the wall a n d the floor be chosen with care.  While  the upper levels of the atria are relatively insensitive to the surface reflectances, the lower levels are, and therefore it is necessary to ensure that the surface reflectances are chosen in such a m a n n e r as to ensure that the working areas i n the adjacent spaces will have a reasonable m i n i m u m daylight factor.  106  In practice, the m a x i m u m that m a y be achieved is 75% reflectance for the wall a n d the  floor.  F o r a well index of 1.95  (under  a predetermined  set of conditions), the  illumination will range f r o m 310 lux at points close to the atria to 14 lux for points at the back of the adjacent office space. T h e well a n d the spaces adjacent to it are also affected b y the changes i n the area of openings such as windows in the walls.  T h e size of the openings affect the available  surface area, which also determines the amount of light reaching the lower levels.  For  larger openings, the daylight factors are higher (greater illumination), whereas for smaller openings they are not. T h e differences i n the light levels between the top a n d the lower reaches of the atria are significant. H o w e v e r , for smaller openings, the distribution of light is more uniform at different well indexes of the atria.  Similarly, light projected into the occupied spaces also has a  comparatively u n i f o r m distribution.  F o r 75% opening of the wall a n d 25% reflectivity of  the wall surface, illumination levels ranged between 60-485 lux: f r o m well index 1.95 to 0.0375.  F o r the same wall reflectivity, with 25% openings, the illumination  ranged  between 30-200 lux. F o r openings beyond 50% of the wall areas, the daylight factors do not increase as m u c h with s m a l l changes in the size of the opening as they do when the increase is for openings between between 0 - 50% of the wall areas.  W h e n the surface reflectance of the  walls are low, the differences in the daylight factors i n the adjacent space, especially at the lower levels, for different opening sizes of the walls are insignificant. F o r a given reflectance there are considerable differences i n the illumination levels between  the top a n d the ground levels of the spaces surrounding the atria.  Small  differences i n the higher reflectivities produce large differences in the daylight factors (and illumination values) as compared to similar differences i n the lower surface range.  reflectance  T h i s is especially so when the area of the wall surface available for reflection is  comparatively high as i n 25% opening of the wall facade.  F o r 75% openings of the wall  107  facade, the illumination values at 0.6m from the a t r i u m well ranged over 310 lux at level 1 and 2400 lux at level 5.  V e r y high illumination values at the upper levels are quite  unneccessary, as in top lit atria, the points in the adjacent office space are closest to the source of light. In fact, there m a y be problems of glare at these locations. A t locations at the back of the spaces adjacent to atria, however, the differences in the daylight factors are not significant for any change in the reflectance or the opening on the wall surface.  T h e daylight factors are higher for points near the opening of the  adjacent space, a n d fall rapidly as the distances f r o m the atria well increases.  In all cases,  the illumination values seldom increased over 350 lux for points at/beyond 5.4m from the a t r i u m well.  In higher well indexes, this was a p r i m a r y concern, especially when there is  no contribution b y the  floor surfaces  to enhance  Supplementary lighting is therefore necessary.  illumination within the side  spaces.  A simple means to achieve this would be  d r a w i n g daylight into the space by using windows and similar openings along the exterior facade of the office space.  Where this is not possible or insufficient, artifical lighting will  have to be used. It has been established by this study that floor reflectivity plays a key role in the availabilits' of daylight, especially in the lower levels. T o increase the available light in the ground floor, increasing the floor reflectance will enhance the levels of illumination. L i n i n g the edge of the floor with a high reflective surface increases the daylight factors in the space adjacent to it.  B u t the increase at locations close to the atria well is  dependent on the nature of openings on the wall facade: its size and its location within the wall.  If the openings are s m a l l and placed in the center of the wall facade, increasing a  large a r e a of the perimeter reflectivity of the floor will increase daylight levels in the adjacent  spaces.  If the  openings  are  large,  a  comparatively  reflectivity along the perimeter of the atria floor will suffice. the entire  floor is changed or increased intermittently,  smaller  area  of high  Whether the reflectivity of  supplementary illumination in  spaces adjacent to the atria in the lower levels are required to be provided.  108  Since lighting is additive, at a given point, the illumination level is the s u m of values f r o m different directions a n d light sources.  In most cases, the external wall of the  office space can be successfully used to balance the interior illuminance. T h u s , the a t r i u m space can  be successfully  used to  draw  light into the  interior  and provide a n  even  distribution of light in spaces adjacent to the atria. T h i s research set out to demonstrate environmental benefits.  W i t h i n the  scope  that atria m a y be used effectively to serve of daylighting itself, continuing studies  various aspects of this research m a y be explored.  on  Confining the study to top-lit atria, a n d  with no projections on the wall facades, further study m a y be done u s i n g the same well indexes, but for different proportions of the atria well. gradually,  from the  top to the bottom of the  Increasing the area of the openings  well with subsequent  increases in the  reflective areas f r o m the edge to the core m a y provide higher daylight factors i n the lower reaches of the atria.  F u r t h e r study m a y also be done changing the reflectivity of specific  parts of the floor for different areas of openings on the walls to understand how lighting in the adjacent spaces in the lower reaches of the atria are affected. Simulating vegetation  and water on the  atria  floor to establish its effects on  daylight in the lower levels is another important dimension to be explored. atria floors are lined with landscape features such as vegetation with furniture and sculptures also.  and water,  V e r y often, sometimes  If they are to be used in an atria serving daylighting  function, their location must be carefully chosen.  W a t e r can act as a reflective agent, but  vegetation acts as a n absorptive agent. Certain guidelines can thus be d r a w n f r o m this study which m a y be s u m m a r i z e d as follows: 1.  T h e most challenging factor in designing atria for daylighting is the compromise  that will have to be made between the area of openings on the wall facade and the surfaces available for reflection.  In the study conducted b y Cole and H u i (1988), it was  suggested that the size of the openings be changed as the well index increases,  that is,  109  smaller openings on the upper levels gradually increasing to larger openings at the lower levels. This will provide sufficient area for reflecting light to the lower reaches of the atria. 2. If the size of the opening is to remain constant, the daylight factors in the adjacent spaces can be increased by increasing the surface reflectivit}' of the walls. 3.  At the back of the adjacent space, the daylight factors do not increase  appreciably, either with increase in the area of the surfaces available for reflection or the reflective surfaces of the walls. Instead, distribution of light in the side spaces can be obtained by increasing the floor reflectivity. 4.  Illumination levels in the well and in the occupied spaces vary greatly with  increase in distance from the light source in top-lit atria. 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