Norwegian University of Science and Technology Faculty of Architecture Department of Building Technology DAYLIGHTING IN LINEAR ATRIUM BUILDINGS AT HIGH LATITUDES av Barbara Matusiak Doktor ingeni0ravhandling September 1998 DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. ACKNOWLEDGEMENTS I wish to express my gratitude to my advisor, professor 0yvind Achehoug, for an excellent guidance and support during the whole process of creating, developing and writing of the thesis. I am also grateful to professor B. Cold for giving me inspiration at the beginning, and professor A. G. Hestnes for discussing of the work at the end of the process. A special recognition to Paul Littlefair for guidance in use of the artificial sky at BRE in Watford, GB, and Raphael Compagnon for helping me with Radiance simulations. My appreciation also goes to Birgit Sudb0 for the help with all the expected and unexpected computer problems and my fellow doctoral students: Anne, Beate, Chandani and Heidi for all the discussions and the nice atmosphere we had. This project could not have succeeded without the financial support provided by the Hydro Aluminium dr.ing. programme at NTNU. My stipend was financed by the Faculty of Architecture, Planing and Fine Arts at NTNU. Special thanks to my husband Miroslaw for the moral and spiritual support and to my children: Julia, Martin and Pawel for all the unforgettable moments we had together. I SUMMARY The content of the project can be divided into three parts that correspond to the three objectives of the thesis formulated in chapter 1. The first part is dedicated to visual comfort and is included in chapter 2. New criteria for visual comfort based on knowledge about visual perception, are proposed. The visual environment of an indoor space is divided into form, shape, and space, and visual comfort in vision of objects from each of these categories is discussed in detail. The modelling ability of light connected to the vision of small three-dimensional objects is discussed comprehensively. Radiance simulations are used for analysing the luminance distribution on small shapes. A method for estimating the modelling ability of light, using the inter-reflection calculations, is also proposed. At the end of chapter 2 visual comfort in atrium buildings is discussed. The second, theoretical part is included in chapters 3 and 4. Chapter 3 consists of simplified calculations of the daylight factor in linear building structures, using the projected solid angle principle. The calculations are done for uniform sky and for CIE overcast sky conditions. The results of calculations are compared to experimental results described in chapter 6. In chapter 4 simple diagrams are created on the base of calculation results of the mean daylight factor in rooms adjacent to a narrow street, using the Superlite program. The resulting formulas and tables from chapter 3 and diagrams from chapter 4 can be used as a simple design tool. In the third main part of the project, the daylighting strategies for linear atrium buildings at hi gh latitudes are developed and examined. This part is started in chapter 5 where daylighting strategies for linear atria are proposed and described. The strategies are divided into three groups: —> the atrium space and facades as light conductor/reflector, —> the glass roof as a light conductor, and —> light reflectors on the neighbouring roof. The strategies connected to the atrium space and facades are further divided into passive and active. The active strategies rely on the use of daylight systems in the atrium space, such as specular reflectors or laser cut panels. The passive strategies rely on the design of the facades. Two facade alternatives were examined. Facade A had glazing area that varied with floor level. The design of this facade was to a large degree based on the results of the Superlite calculations from chapter 4. Facade B had glazin g types that varied with floor level. The design of both facades resulted in balanced daylighting of the spaces adjacent to the atrium on all floor levels. The strategies connected to the glazed roof included different configurations of glazing: horizontal, single pitched, double pitched, and the use of laser cut panels and prismatic panels in the glazed roof. Three different shapes of reflectors on the neighbouring roof were examined: a flat reflector, a parabolic reflector and a parabolic concentrator. Strategies from all three groups were examined on a physical model in 1:20 scale in the artificial sky of mirror box type at Building Research Establishment in Watford near London; the results are presented and discussed in chapter 6. Simulations with artificial sun were done at the Department of Electrical Engineering in the Norwegian University of Science and Technology in Trondheim; the results are included in chapter 7. n The strategies were also simulated using the Radiance rendering program. The program enabled parametric studies of the most pro mising alternatives, creating computer images, and calculation of the visual comfort probability, chapter 8. The results from model studies were compared to the results from Radiance simulations, and the final conclusions are formulated in chapter 9. All the active daylighting systems designed for use in the atrium space or on the atrium facades have a huge potential for use in atrium buildings. The glazed roof obstructs about 40- 50% of diffuse skylight The active daylight systems make it possible to utilise the remaining 50-60% effectively by redirecting diffuse skylight from the excessively daylit zones to the areas where it is most needed. In this way the negative effect of the glazed roof can be to a large degree reduced. From the strategies connected to the glazed roof the negatively sloped glass was found to be the best alternative for glazed roofs at high latitudes. All alternatives with the light deflecting panels on the roof performed very well. They multiplied the daylight levels in the atrium in the desired seasons. The alternative with laser cut panels sloped by 30° gave the best results of all alternatives, both in winter and in spring/autumn. Prismatic panels performed better as a sun shading. The study with roof reflectors showed that the flat one performs best, especially as an operable device. The thesis is supplemented with a list of the terms and definitions used in the thesis, appendix 1, and with calculations of the light transmission factor of different types of glass, appendix 2. HI TABLE OF CONTENTS CHAP. 1 INTRODUCTION 1 1.1 Motivation 1 1.2 Objectives 4 1.3 Methods 5 CHAP. 2 VISUAL COMFORT 6 2.1 Visual perception 8 2.1.1 The perception of brightness and darkness 8 2.1.2 Adaptation 8 2.1.3 Simultaneous contrast 8 2.1.4 Border contrast effect 8 2.1.5 Successive contrast 9 2.1.6 Illusory contours and forms 9 2.1.7 Colour perception 9 2.2 Glare, a sign of discomfort 10 2.3 Criteria of visual comfort 14 2.3.1 Criteria for visual comfort in vision of form 15 2.3.2 Criteria of visual comfort in vision of shape 20 2.3.3 Criteria of visual comfort in vision of space 28 2.3.4 Conclusions about visual comfort 30 2.4 Visual comfort in linear atrium buildings 30 2.4.1 Visual comfort in the atrium space 30 2.4.2 Visual comfort in adjacent rooms 34 CHAP. 3 SIMPLIFIED DAYLIGHT FACTOR CALCULATIONS 37 3.1 Calculations of sky factor for uniform sky 37 3.1.1 Sky factor on the floor 37 3.1.2 Vertical sky factor on facades 39 3.2 Calculation of the sky factor for the CIE overcast sky 40 3.2.1 Sky factor on the floor 40 3.2.2 Sky factor on the facades 44 3.3 Calculations of daylight factor 46 CHAP. 4 SUPERL1TE CALCULATIONS 49 4.1 Description of the calculation model 49 4.2 Calculations for the 5 floor linear atrium or street 50 4.3 Calculations for the 4 floor linear atrium or street 51 4.4 Conclusions 51 IV CHAP. 5 DESIGNING DAYLIGHT SYSTEMS FOR LINEAR ATRIA 53 5.1 Materials used in the project 53 5.1.1 Traditional materials 53 5.1.2 Light redirective materials 55 5.2 Presentation of alternative strategies 57 5.2.1 Atrium space and facades as a light conductor/reflector 57 5.2.2 Glass roof as a light conductor/reflector 60 5.2.3 Light reflector on the neighbouring roof 62 Chao. 6 MODEL STUDIES UNDER AN ARTIFICIAL OVERCAST SKY 64 6.1 Design of the base model 64 6.2 Sky details 66 6.3 Methods of measurement 66 6.4 Presentation of daylight systems 67 6.4.1 Atrium space and facades as a light conductor/reflector 67 6.4.2 Glass roof as a light conductor/reflector 69 6.4.3 Light reflector on the neighbouring roof 70 6.5 Comparison of facade alternatives 71 6.5.1 Facade alternatives A, B, C and Cx in the atrium space 72 6.5.2 Analysis of the luminance distribution on facade A 72 6.5.3 The impact of the choice of the facade alternative on the illuminance levels in adjacent rooms 75 6.5.4 Visual comfort in rooms adjacent to the atrium for alt A 79 6.6 Importance of the reflectance of atrium surfaces 82 6.6.1 Comparison of B-altematives on the street 82 6.6.2 Comparison of B-altematives in the room 84 6.7 Significance of the glass slope on the first floor 86 6.8 Comparing different active daylight strategies 87 6.9 Discussion of the significance of the roof glazing 98 6.10 Laser cut panels and prismatic panels on the roof 99 6.11 Reflectors on the neighbouring building 101 CHAP.