Energy performance of evacuated glazings in residential buildings

This paper presents the results of a study investigating the energy performance of evacuated glazings or glazings that maintain a vacuum between two panes of glass. Their performance is determined by comparing results to prototype highly insulated superwindows as well as a more conventional insulating glass unit with a low-e coating and argon gas fill. The DOE-2.1E energy analysis simulation program was used to analyze the annual and hourly heating energy use due to the windows of a prototypical single-story house located in Madison, Wisconsin. Cooling energy performance was also investigated. The results show that for highly insulating windows, the solar heat gain coefficient (SHGC) is an important as the window's U-factor in determining heating performance for window orientations facing west, south, and east. For other orientations in which there is not much direct solar radiation, the window's U-factor primarily governs performance. The vacuum glazings had lower heating requirements that the superwindows for most window orientations. The conventional low-e window outperformed the superwindows for southwest, south, and southeast orientations. These performance differences are directly related to the SHGCs of the various windows analyzed. The cooling performance of the windows was inversely related to the heating performance. The lower SHGCs of the superwindows resulted in the best cooling performance. However, the authors were able to mitigate the cooling differences of the windows by using an interior shading device that reduced the amount of solar gain at appropriate times.