Theoretical Impact of Building Facade Thickness on Daylight Metrics and Lighting Energy Demand in Buildings: A Case Study of the Tropics

In daylighting design, variation of building facade thickness (f) will result in variation of the daylight opening areas, which in turn will modify the values of daylight metrics within the space. However, studies dedicated to investigating the impact of varying f on indoor daylight metrics are relatively scarce. This study, therefore, aims to assess the theoretical impact of various facade thicknesses on various daylight metrics and lighting energy demands in a reference office space. Analytical calculations are performed using an outdoor diffuse illuminance profile of a tropical city. The building facade thickness values are varied within 0-0.50 m, at window-to-wall ratios (WWR) of 25%, 50%, and 75%. Based on sensitivity analysis, it is found that variation of f yields different impacts on the observed metrics, with sDA(300/50%) being the least influenced. Among all metrics in the central calculation point, DA(300), UDI-a, and UDI-a ' yield relatively small coefficients of variation, and thus, have the lowest uncertainty with respect to f. Among all metrics for the entire room, sDA(300/50%) and sUDI-a(50%) have the lowest uncertainty, with interquartile ranges of no more than 0.4%. Overall, the contribution of this study is providing insight into the impact of facade thickness on various daylight metrics in indoor spaces, particularly in the worst-case scenario under the standard CIE overcast sky.