Low Emissions Window Film Saves 29% in Energy Use
Up to 34% of commercial building heating and air conditioning energy is lost through old, single pane windows which are especially prevalent in older facilities. A newly available window film can be applied to these existing windows to help with reflecting solar heat in warmer months and insulate interior warmth during the colder months—saving 29% in heating and cooling energy use and improving comfort.
While we have been able to use conventionally applied solar control window film to reduce solar heat gain, a new kind of applied window film is available which, until now, was available only as part of a factory-produced window unit. This new film, tested through GSA’s Green Proving Ground program, combines the solar control functions of standard solar control film with the newly available insulating power of a low emissivity (low-e) coating. Adding this low-e insulation improves the film’s efficiency in all seasons, compensating for diminished solar heat gain in the colder months.
Researchers from Lawrence Berkeley National Laboratory (LBNL), working with GSA through the Green Proving Ground program, assessed the new film at two GSA locations: the James V. Hansen Federal Building in Ogden, Utah, and the Earle Cabell Federal Building in Dallas, Texas. Compared to clear, single-pane glass windows, a version of the low-e film averaged 29% energy savings in building perimeter and has a projected payback between two and six years.
During measurement and verification at both sites, LBNL researchers compared the performance of single-pane windows covered with the low-e film to both clear single-pane windows and single-pane windows equipped with traditional solar control film. Temperature and solar radiation data were recorded for six months at the Ogden site and for one year at the Dallas site. With the data sets collected, researchers used software to model annual energy savings for buildings in other climate zones such as Chicago, Miami, Minneapolis, Phoenix, and Washington, DC. Comfort and satisfaction surveys were issued to building tenants before and after low-e film installation to measure its perceived effectiveness. Most occupants surveyed recommended adoption of the low-e film and noted reductions of glare and window-related temperature fluctuations.
Aaron Rock, GSA Building Manager for the Hansen Federal Building in Ogden, UT praised the low-e film’s installation in his building. “Unlike replacing single-pane windows with double glazing, installation of the low-e film is not disruptive, and it can be done in stages and during off hours. We are planning to retrofit the other floors of our building.” The low-e film consistently achieved the best incremental performance of any of the applied films considered and is recommended for deployment in a wide range of climates and window configurations in GSA buildings nationwide. To learn more, visit GSA’s Green Proving Ground program.