The Influence of Roof Fenestration on Daylight Distribution in an Atrium Space Under Tropical Sky Conditions
A parametric study was done to evaluate the daylight performance in atrium buildings focusing on the effect of roof fenestration on the atrium space under a range of sky conditions. The interaction between various roof configurations and daylight conditions inside the atrium space was also studied. In achieving this objective, the work began with a field study using scale models under real sky conditions in a tropical region. The data produced were used to simulate more complex conditions by running a simulation study using the IES-3178 VE-Pro (IESRadiance) program suite for daylighting simulations on a full-scale atrium. The photometry and geometry of the test modules were carefully reproduced. The surrounding and daylighting environment of the physical model under real sky conditions were also simulated. The evaluation of daylight performance under real sky conditions was very challenging due to dynamic changes and fluctuations in sky conditions throughout the day. The changes were controlled in the simulation studies by maintaining a 2% atrium surface reflectance in order to study the transmittance by the roof fenestrations.
For real sky conditions, the factors considered were atrium design such as the form, skylight shapes, floor height, surface reflectance and glazing transmittance. After the real sky study, a comprehensive simulation was conducted in a much more complex environment which included many parameters from both indoor and outdoor conditions. The external factors refer to sky conditions and the sun’s position such as solar altitude and elevation with respect to time.
Four models were developed to perform the daylighting performance analyses. The models used different roof fenestration designs and structural truss systems: flat, pitched, pyramidal-gridded and saw-tooth. It was found that structured roof forms reduce daylight levels in the atrium well by 55%. A high contribution of daylight penetration occurs at the centre nearest to the atrium opening. The transmittance of the atrium roof structure also decreased the illuminance level at the lowest corners of the atrium space by 50%. Under overcast skies, the illuminance levels decrease even more at the corners of the atrium floor, especially for the north- and west-facing atrium surfaces for all types of roofs. Not surprisingly, the flat roof performed well in maintaining the acceptable limit of maximum light utilisation and was most consistent in terms of light distribution across the atrium floor. Meanwhile, the pyramidal-gridded roof type performed better in terms of daylight contribution at approximately 50%. The pitched roof was found to be less consistent and had poor distribution, especially at low transmittance levels. These results will aid the atrium designer in making decisions on the optimal design strategy for daylighting and energy efficiency.
KeywordsDaylight performance Atrium Roof fenestrations
The authors thank the Faculty of Architecture, Planning and Surveying, Universiti Teknologi MARA, INTEC Education College and ISESCO for the support of this work and the production of this chapter.
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