Light transmittance characterization and energy-saving analysis of a new selective coating for in situ window retrofit

Windows are often pointed to as the weakest elements in building facades, given their low thermal resistance. Consequently, they are a main focus during building retrofits, when their substitution is often considered an expensive but necessary choice. This article describes a new high-performance glazing coating, which can be used for the in situ retrofit of existing windows. The easy application of this new liquid-applied coating on the internal side of the glazing makes it possible to reduce the solar heat gain coefficient of an existing window substantially and quickly, without interrupting the building occupancy. Experimental characterizations of light transmittance and thermal characteristics are presented in this article. Although the new coating allowed a reduction in the visible transmittance (VT) of only 0.1 compared to nontreated insulating glass units (IGUs), it proved to reduce significantly the solar heat gain coefficient (SHGC) of the investigated IGUs to values below 0.45. This article also reports the results of aging studies aiming at assessing the risks of long-term performance reductions of this new liquid-applied coating. Finally, the results of energy simulations investigating the energy-efficiency improvements when this coating is applied to different kinds of windows in Canada are reported.