Most heat loss from within the interiors of an architectural structure is through glass windows and doors than through other components. Thus, finding ways to make glass in windows and doors more thermally insulating is important to improve the energy efficiency of a building. One of the techniques usually applied is to combine two window construction procedures — vacuum glazing and electrochromic glazing. Doing this ensures improved thermal comfort while limiting the use of auxiliary space heating and artificial light. This guarantees very low heat loss and variable light transmission, and also controls glare from day lighting.
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 are sealed with solder glass or indium. The interior faces of one or both glass sheets usually have a transparent, low-emittance coating. Glass 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. Visible light transmittance by EC films can be varied between 8% in their coloured state and up to 80% in the bleached state by applying a 1–2V DC switching voltage.
Electrochromic vacuum glass combines EC and VG technologies. This 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.
High densities of nodes in and around the pillars are used to represent the heat transfer. When the EC layer faces inward, glazing surface temperatures become too high for occupant comfort and result in damage to the EC VG system. The temperature difference between the two glass panes of the VG result from the high thermal resistance of the vacuum gap; the temperature difference between the panes separated by the EC layer result from the EC layer absorbing heat.
Electrochromic vacuum glass is more thermally insulating than a standard double pane window and is comparable to a good triple pane window. Windows made from Electrochromic vacuum glass improve the energy efficiency of buildings while keeping occupants thermally comfortable.
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