Design optimisation for window size, orientation, and wall reflectance with regard to various daylight metrics and lighting energy demand: A case study of buildings in the tropics

Design optimisation problems of window size and façade orientation in buildings have been investigated many times, with regard to energy and comfort criteria. To indicate daylight availability in indoor spaces, a number of daylight metrics have been proposed, but those metrics are not always fully accounted in the optimisation process. Also, most studies were conducted for locations with high latitude, where the sun is located most of the time either at the south or at the north part of the sky hemisphere, which is not the case in the tropics. Therefore, this article presents a simulation study to investigate the influence of window-to-wall ratio (WWR), wall reflectance, and window orientation on various daylight metrics and lighting energy demand in simple buildings located in the tropical climate. A simple approach for the multi-objective optimisation was proposed by classifying the results in six pairs of two different performance indicators. Solutions in all Pareto frontiers were filtered against the defined target criteria, and were accepted into the optimum solution space if they belong to at least 4 out of 6 Pareto frontiers, and were ranked either in the order of their mean distance to the utopia points, or in the order of number of times they belong to a Pareto frontier. Three optimum solutions are found, all of which belong to four Pareto frontiers. The most optimum solution with the least mean distance to the utopia points is the combination of WWR 30%, wall reflectance of 0.8, and south orientation. The proposed approach enables one to observe the inter-relationship between the involved performance indicators, while providing a possibility to visualise the boundaries of the solution space.