A parametric approach for achieving optimum daylighting performance through solar screens in desert climates

Daylighting provision gives a significant contribution to the enhancement of the indoor environment. However, in desert climates spaces are exposed to direct solar radiation, leading to a non-uniform daylight distribution and excessive heat gain. The literature proves that the use of a shading device may solve these problems. In this daylighting study, a parametric approach was implemented where all combinations of five screen parameters (window to wall ratio, louvers count, louvers tilt angle, screen depth ratio, and screen reflectivity) were computed. This generated 1600 different screen configurations based on the predefined range of each parameter. Two consecutive phases were performed in which the Illuminating Engineering Society (IES) metrics, Spatial Daylight Autonomy (sDA300/50%), Annual Sunlight Exposure (ASE1000/250 h), Daylight Availability as well as Annual Daylight Glare Probability (DGP), were examined. Diva-for-Rhino plug-in for Rhinoceros was used to interface Radiance and Daysim while Grasshopper plug-in for Rhinoceros was used to generate 1600 solar screen's configurations parametrically and to automate the simulation process. The simulated case study was a generic south-oriented classroom located in Cairo' desert in Egypt. A parallel computing procedure, by which multiple Radiance simulations can be run, was used to find optimal solutions. These solutions were characterized by maximum daylit area without excessive solar penetration. The general tendency of each parameter and the interaction between them was examined. Simulation results demonstrated the trend of converging solutions starting from 1:1 depth ratio with downward tilted angles. Finally, the influence of increasing screen reflectivity in enhancing daylighting performance was illustrated.

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