Electrochromic vacuum glazing may improve thermal comfort in buildings

Abstract

In general, more heat escapes through glass (windows) than through the other materials in a structure. Thus, finding ways to make windows more thermally insulating is important to improving the energy efficiency of a building. We have combined two window construction techniques—vacuum glazing and electrochromic glazing—to provide improved thermal comfort while limiting the use of auxiliary space heating and artificial light. This performance is thanks to the system’s very low heat loss and variable light transmission, which can also control glare from daylighting. A vacuum glazing (VG) comprises two sheets of glass that are separated by a very narrow evacuated space. An array of metal or ceramic pillars holds the sheets apart, and the edges can be sealed with solder glass or indium. The interior faces of one or both glass sheets usually have a transparent, low-emittance coating. Windows made from vacuum glazing are much more thermally insulating than either single pane or conventional double glazed windows. Electrochromic (EC) glazing causes glass to change its tint in response to an applied voltage change. Research in this area and its many potential applications are well documented.1 Visible light transmittance by EC films can be varied between 8% in their colored state and up to 80% in the bleached state by applying a 1–2V DC switching voltage. An ‘EC VG’ combines EC and VG technologies, as shown in Figure 1. Our novel glazing system combines the low-heat-loss properties of VG—a U-value (heat transmittance) of less than 1Wm−2K−1—with the variable transmittance of EC glazing to control solar gain. The first working vacuum glazing2 using a low melt solder glass to form a contiguous edge seal at temperatures above 450◦C was reported in 1989. Many types of soft, low-emittance coatings Figure 1. This schematic diagram shows the various components of an electrochromic vacuum glazing.