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October 11, 2012 -
Windows & Exterior Walls
Today's tip is to consider solar window film for greater energy efficiency. Solar heat gain through windows is responsible for roughly one-third of a building's cooling load, according to the Department of Energy. That makes applying solar window film a logical step in reducing solar heat gain and improving the energy efficiency of a building.
Solar window film is applied to the inside of a window, where it reflects and absorbs heat from sunlight, thus reducing heat gain. Near-infrared radiation makes up 53 percent of the solar spectrum, visible light 44 percent, and ultraviolet 3 percent. When rays from the sun hit a window, some of the energy is absorbed and some is reflected by the window, but most is transmitted through the glass.
A pane of clear glass reflects about 6 percent of solar radiation, absorbs 5 percent, and transmits the remainder. Installing solar control window film increases the amount of solar energy both reflected and absorbed by the window. Most films have a thin metallic coating, made up of aluminum, stainless steel, silver or a combination that reflects and absorbs solar radiation.
The most important performance measurement of window film is the solar heat gain coefficient (SHGC), says Darrell Smith, executive director of the International Window Film Association. SHGC measures the total amount of solar energy transmitted into the room. The heat rejection of window film can be as high as 80 percent, says Smith.
A reduction in solar heat gain can translate directly into fewer kwh used for cooling. What’s more, by reducing the amount of cooling needed during peak periods, demand charges can also be reduced. Some utilities offer rebates and other incentives for installation of window film because of its ability to help save energy.