DESIGN: Parameters

Window Area

Window area or window-to-wall ratio (WWR) is an important variable affecting energy performance in a building. Window area will have impacts on the building's heating, cooling, and lighting, as well as relating it to the natural environment in terms of access to daylight, ventilation and views. The window-to-wall ratio is the measure of the percentage area determined by dividing the building's total glazed area by its exterior envelope wall area.

Facades can be designed using a higher percentage than the code prescriptive maximum by using high-performance glazing systems (including dynamic systems) that may or may not be used in combination with interior and exterior shading strategies. These designs reduce the unwanted solar gain through the large window area, while still allowing for natural daylight to enter spaces which results in reduced electric lighting use.

This image shows the comparative results of 5 scenarios for a south-oriented office zone in Chicago. The results illustrate that using a large window with high performance glass has energy performance that is better or equal to a small window with poor performing glass.

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