Do Window Films Save Energy?

According to the California Energy Commission, as much as forty percent of a building’s cooling requirements are a function of heat entering through existing glass. Even a small amount of glass on the south or west side of a building can result in overheating and increased energy costs. Stopping heat at the window is the most effective way to save by lowering temperatures and reducing HVAC operating cost.

The best place to stop heat and reduce air conditioning cost is at the window. However, the most energy efficient window film is not necessarily the film that blocks the most heat.

Applied window film is the least expensive solution to mitigate the impact of rising energy cost from too much solar heat entering windows. The good news is conventional tinted and reflective applied window films successfully block a significant amount of solar heat.

The bad news is that these same films reduce a significant percentage of visible sun light. Most of these films are highly reflective in daylight giving them a mirror like appearance when viewed externally. In retail establishments visible sun light is reduced inside the store and shoppers outside cannot clearly see inside.

Most conventional window films transmit less than 34% of visible sun light, a good 36% less than the 70% necessary to be undetected by the naked eye. The result as building interiors are correspondingly darkened, often requiring the use of increased energy costs from the additional illumination. This may lead to higher energy consumption that may increase inside temperatures requiring more air-conditioning. Increased energy costs defeat the major benefit of the energy efficient films – cost savings.

The use of conventional tinted and reflective heat-blocking window films can negatively impact building occupants by denying them adequate levels of natural sun light. Studies conducted by the U.S. Department of Energy and others document a relationship between low levels of natural sun light and less than optimum well being and productivity.