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The Effect of Window-to-Wall Ratio on Building Energy Performance

Abstract

The energy performance of buildings is strongly influenced by the design and characteristics of the building envelope. Among the various components of the building envelope, windows play an important role in determining the amount of solar radiation, natural light, and heat transferred between the indoor and outdoor environments. The window-to-wall ratio (WWR), which represents the proportion of a wall surface occupied by windows, can significantly affect building energy consumption, thermal comfort, daylight availability, and overall building performance. Appropriate consideration of WWR is therefore essential in the design of energy-efficient buildings. This study examines the effect of window-to-wall ratio on building energy performance. The WWR influences the amount of heat entering and leaving a building, as well as the availability of natural daylight within interior spaces. A high WWR may increase daylight availability but can also result in greater solar heat gain and heat loss, potentially increasing the demand for cooling or heating. Conversely, a very low WWR may reduce unwanted heat transfer but can limit natural daylight and increase dependence on artificial lighting. The orientation of windows is another important factor affecting the relationship between WWR and energy performance. Windows facing different directions receive varying levels of solar radiation throughout the day and year. The use of appropriate WWR in combination with building orientation, external shading devices, glazing type, and window placement can help control solar heat gain while maintaining adequate daylight. These design considerations are particularly important in tropical climates, where excessive solar radiation can increase indoor temperatures and cooling requirements. Window characteristics also influence the energy performance associated with different WWR values. Factors such as glazing type, glass thermal properties, visible transmittance, window frame materials, and shading systems can determine the amount of heat and light transmitted through windows. Energy-efficient glazing and appropriate shading devices can reduce unwanted solar heat gain while allowing sufficient daylight to enter the building. Therefore, WWR should be considered together with other window and building envelope characteristics during the design process. An appropriate window-to-wall ratio can provide both energy and environmental benefits. Optimizing WWR can reduce the energy required for mechanical cooling and artificial lighting while improving indoor thermal and visual comfort. However, the most suitable WWR varies according to climatic conditions, building orientation, building type, occupancy patterns, window properties, and local environmental conditions. Excessive glazing without adequate solar control can increase cooling loads, while insufficient glazing may reduce daylight availability and negatively affect the indoor environment. This study assesses the effect of different window-to-wall ratios on building energy performance, with particular attention to energy consumption, solar heat gain, daylight availability, and thermal comfort. The study is expected to identify appropriate WWR considerations for improving the energy efficiency of buildings while maintaining suitable indoor environmental conditions. The findings will provide useful information for architects, engineers, building designers, and other stakeholders in developing energy-efficient and climate-responsive buildings through effective window and façade design.

Keywords: Window-to-wall ratio, Building energy performance, Energy efficiency, Building envelope, Solar heat gain, Daylighting, Thermal comfort, Window design, Glazing systems, Solar shading, Building orientation, Energy consumption, Sustainable building design, Climate-responsive design.