Assessment of the impacts of window-to-wall ratio and overhangs on building energy performance – Kabul, Afghanistan

Abstract

Windows have the potential to save energy in a significant way. Therefore, the analysis and optimization of the Window-to-Wall Ratio (WWR) play an important role in improving energy efficiency in buildings. Windows are always beneficial to utilize daylight and reduce lighting energy demand. However, solar heat gain is advantageous during cold days and disadvantageous on hot days. As the configuration of the window areas varies according to the geographical location, the objective of this study is to evaluate the impact of WWR on the energy performance of buildings in the cold semi-arid climate of Kabul, Afghanistan. In this study, various energy simulations were conducted for three types of building shapes (Square, Rectangle, and “L”-Shape) to determine the most energy-efficient proportion of windows and overhang sizes in different cardinal directions. Based on the simulation results, windows on south façades have notable energy-saving potential in Kabul's climatic conditions. However, increasing the window size on north, east, and west façade leads to an increase in the total heating and cooling energy consumption. The optimal WWR of the south façade window for square, rectangular, and “L”-Shaped is 0.7, 0.55, and 0.55, respectively. Additionally, the findings indicate that overhangs in all orientations slightly affect the total energy demand as they only reduce cooling load. The study concludes that optimizing the windows on the south façade reduces energy demand by up to 8.13% if no windows are provided in other directions, while the total energy consumption rises by up to 36% as the WWR on the north, east, and west façades increase from 0 to 0.8.