Multi-objective optimization of daylight performance and thermal comfort in classrooms with light-shelves: Case studies in Tehran and Sari, Iran

Abstract

In educational buildings, an efficient daylight design has significant influences on student’s visual comfort, well-being and productivity while it offers significant benefits for reducing lighting energy consumption. Besides visual discomfort, the excess of daylight entry to space will cause disadvantages, including building overheat. Therefore, it is essential to define the optimal design for daylight control devices. In previous studies, daylight performance of light-shelf as a window-attached daylight control device has been studied. This paper aims to investigate the effect of sky cloudiness on the optimum light-shelf properties defined for typical classrooms. In addition, the optimum properties of the light-shelf for classrooms in two cities have been defined, which had not been addressed in Iran’s national codes and guidelines. The methodology used is based on three steps: daylight optimization of light-shelf parameters, thermal comfort analysis for selected solutions, and choosing the best option. Four parameters of light-shelf, including height, length of the exterior part, length, and angle of inner part, have been considered as variables. Using Octopus optimization algorithm in Rhinoceros, Grasshopper simulation tool, a multi-objective algorithm has been applied to find the optimum combination of the parameters based on daylight performance indicators. Thermal comfort analysis has been conducted for selected solutions with optimized light shelves using Openstudio. The results indicated that applying light-shelf in Tehran with less sky cloudiness is more effective than Sari in terms of providing both daylight and thermal comfort, especially for cases with more window to wall ratio (WWR). Sari, the case with lower WWR, does not necessarily have less Annual Solar Exposure, even with an optimized light-shelf. Hence choosing the best option without comparing daylight metrics for optimized solutions of various WWR is misleading. According to the results, although the best options are different in the cities as the effect of sky cloud cover, the optimum light-shelf properties are the same in light-shelf height, exterior, and interior length, while the pivot angles vary. There is also a relation between rotation angle and daylight availability regarding WWR in each city. Considering daylight and comfort issues, WWR for the best option in Tehran is greater than Sari. The study results provide useful information for designers for choosing the optimal properties of light shelves and the best option for design in the two mentioned cities.