Daylight Performance of a Naturally Ventilated Building as Parameter for Energy Management

Daylight is an important element of energy efficient buildings. Energy savings from artificial lighting during the daytime can have significant impact on the energy sustainability residential buildings. For a city like Mumbai, where the buildings have limited access to daylight due to the sprawling of densely packed high rise buildings, energy saving from daylighting can be an effective driver of sustainability. Under this purview, it is prudent to evaluate the effects of various building design elements like orientation and window-to-wall ratio (WWR) on energy saving potential through daylighting. In this study, two parameters of daylight incidences: Useful Daylight Illuminance (UDI) and annual light exposure, were studied to understand the daylight performance of a high rise residential building. UDI values were then reiterated by varying the orientation and WWR. The results showed that the building performed best at the South-East orientation with a WWR of 50% which allowed 63% more ambient illuminance in the functional space. This study also unveils the paradigm that ambient illuminance inside the functional space of the building may be independent of total incident annual light exposure in the rooms. That means more annual exposure does not necessarily means better lighting conditions within the indoor functional space. Hence, this study creates a way forward in designing energy efficient buildings using UDI as a daylight performance metric.