Determining the optimal window size of office buildings considering the workers' task performance and the building's energy consumption

In office buildings, the workers' task performance and the buildings' energy consumption may differ greatly by window size. Therefore, the purpose of this study was to determine the optimal window-to-wall ratio (WWR) considering the workers' task performance and the energy consumption in office buildings. To analyze the workers' task performance by WWR, cognitive tests and the NASA-Task Load Index test were conducted in a virtual environment. To calculate the energy consumption of the office building, building energy performance simulation was conducted using a large office building of the Department of Energy. Finally, multi-objective optimization was conducted to determine the optimal WWR by building facade orientation. As a result, it was shown that increasing the WWR in an office building can increase the workers' task performance and decrease the workers’ task load. The 60% WWR showed the highest task performance and the lowest task load. As a result, the optimal WWRs in the office building were 44.47% for the East facade, 50.58% for the South facade, 44.37% for the West facade, and 40.95% for the North facade. It is expected that this study will help in determining the window size that is suitable for the building facade when designing office buildings that can realize both energy efficiency and a healthy work environment.