Analysis of optimum window-to-wall ratio in Horizontal expanded and vertical expanded windows, Tehran, Iran

Good daylighting design in buildings not only provides a comfortable luminous environment, but also delivers energy savings and comfortable and healthy environments for building occupants. The importance of using daylight in educational buildings is because of the synchrony of operating hours of the school and daylight plenitude the sky. Daylight improves environmental quality and saves energy efficiency by minimizing artificial lighting requirements and thus reducing the cooling load. Window design is a primary sustainable approach in achieving environmental goals and contributes to comfort and satisfaction. This study analyzes the variations of annual thermal energy demand and useful daylight illuminance to determine the optimal Window-to-Wall Ratio (WWR) of a simulated primary school classroom in Tehran in two directions of south and north. Twelve different window sizes in two types of horizontal expanded windows (Height of the window remains constant, the width is varied) and vertical expanded windows (Width of the window remains constant, the height is varied) were compared in two parts, Useful Daylight Illuminance (UDI) and thermal and electricity energy, using Honeybee plugin of Grasshopper. Finding of this research reveals that vertical expanded windows are more energy-efficient in classroom while they give almost the same UDI as horizontal expanded window in both south and north facades. Generally WWR in the range of 25% to 35% in south façade has the best performance in daylight and thermal loads.