How It Works

Reducing Heat Flow Through Windows

Windows are the weak link, thermally speaking, in most building envelopes. Modern windows are much better than old single-pane windows and store-fronts, but they still represent a compromise—we accept their mediocre thermal performance because we want the daylight, views, and ventilation they offer.

Windows and glazing systems allow unwanted heat flow in several ways. They tend to have cracks and gaps around their edges that allow air to leak in or out. They allow heat transfer via conduction across the glass and frames. And they allow heat to radiate through, both as visible light and as invisible, infrared radiation. This solar gain is the biggest source of cooling loads in buildings with large areas of glass.

Awnings Help Reduce Production of Greenhouse Gases

A recent study by the Center For Sustainable Building Research at the University of Minnesota in the US found that awnings provide significant savings on cooling costs, as well as on peak electricity demand. They do this by significantly reducing solar gain through a building's glass surfaces. The study found that awnings can reduce the need for cooling energy in residential applications as much as 33%.  In commercial applications, where there is a much higher percentage of glass to total exterior surface area than in most residential settings, the savings are even more dramatic.

Because awnings and exterior solar screens reduce the cooling energy required at times of peak usage, there is also a decreased need for electricity consumption, and for utilities to supply generating additional generating capacity. This reduces production of the greenhouse gases which contribute to global warming.