Solar-control retrofit films can provide significant cooling savings in commercial buildings, particularly when used in buildings that have single-pane clear windows and are located in warm climates with mild winters. Lawrence Berkeley National Laboratories (LBNL) was commissioned in 2012 by the General Services Administration (GSA) Green Proving Ground to assess the performance of a liquid-applied, spectrally selective absorbing film installed at the Goodfellow Federal Center in St. Louis, Missouri.
Solar-control films reduce the transmission of solar heat energy by increasing the absorbing or reflecting properties of window glass. Spectrally selective controls treat solar energy in the infrared spectrum only, so the finished appearance is essentially clear. The St. Louis study evaluated an absorbing, spectrally selective film that is unique primarily because it is applied as a liquid and then cures into an 8-micron-deep durable window film.
The liquid-applied absorbing film was installed on 25 double-pane bronze windows in five different zones in the three-story, 135,500-sq-foot Goodfellow Federal Center. The researchers monitored the energy performance of treated and untreated windows in comparable control zones over a period of eight months. They also modeled annual energy consumption for a generic commercial-building perimeter zone, using a range of climates, base window configurations, and applied solar-control products, both absorbing and reflective.
When applied to the interior of the double-pane windows in St. Louis, the film saved 8 percent of cooling energy; however, the savings was offset by an increase in heating energy use during the winter months.
LBNL then expanded its assessment by modeling the energy performance of both absorbing and reflective spectrally selective films in a range of warmer climates, where winters are milder than those in St. Louis. Reflective films outperformed absorbing films, reducing HVAC energy use by 29 percent when modeled using single-pane clear windows in warmer climates.
While solar-control retrofit films were not found to be cost-effective for double-pane bronze windows in most climates, the researchers found that the technology is well suited for buildings that have single-pane clear windows and are located in warm climates with mild winters. The absorbing treatments may also provide an advantage for historic buildings where reflected solar radiation might damage exterior wood trim.
