Energy and Economic Savings from Daylighting through Shaded Windows

Daylight is abundant all year in tropical region and daylighting is attractive. However, air-conditioning is commonly used and penetration of solar radiation adds significant cooling load to large commercial buildings. This paper presents experimental and simulation studies on the application of a daylighting scheme where daylight from the sun is shaded and daylight from the sky is used for general lighting up to the depth that it attains substantial benefit in terms of lighting and cooling energy and life cycle cost. The studies utilize multiple slat external shading devices with small slat width that are considered practical for tall buildings where wind loading would not be significant. Northern and southern facades of a building could be effectively shaded by fixed multiple slat horizontal shading devices while similar vertical devices could be applied to eastern and western facades. Such devices allow daylight from sky to pass through and allow comfortable viewing from the interior to the exterior scene. The results show that the use of such devices with the adopted daylighting scheme on windows of appropriate size and suitable type of glazing leads to significant energy and economic benefits. For the northern or southern façade, daylight penetration depth of up to 10m could be attained with the window area from 35% of overall wall area. For the eastern and western façade, larger window area is required for the same depth.