Energy & Cost Impacts: Window Retrofit Films
The energy savings from retrofitting windows with films depends on adequately matching the film characteristics (SHGC, Tvis, and U-value) to the building characteristics (i.e., type, façade orientation, and location). Consulting a dealer/installer before deciding whether a film is suitable for your building is recommended.
Most window films perform a degree of solar heat gain reduction, i.e., they reduce the amount of solar heat that enters the space, therefore helping reduce energy used in cooling the building. Conversely, this may lead to an increase in energy use for heating the building. This effect can be reduced by using films with low-emissivity properties. Another way films can impact energy use is by reducing the amount of visible light admitted into the building. Depending on the capabilities and configuration of the electric lighting system, this can lead to an increase in lighting energy use, although that effect is usually minor when compared with impacts on HVAC energy use.
Building operating cost impacts of window films are mainly two-fold. The first component is due to the value of the energy saved. The second component is due to the value of avoided replacement of interior surface finishes or materials due to reduced exposure to ultraviolet radiation from the sun. While this latter value is not evaluated here, it may be significant for some types of commercial building applications like hospitality or retail.
The energy savings numbers provided in the plots below are illustrative, and based on ranges of building vintages for each commercial building type, for a clear single-pane baseline window. With a double-pane clear window as baseline, results are generally expected to be similar but less pronounced, as the addition of the film results in a smaller relative improvement in SHGC, Tvis, and U-value. In any actual building, energy savings will be affected by particularities of the building, including siting, orientation, window to wall ratio, window type, opaque envelope, building systems, and occupancy.
