Heat-Transport and Solar Transmission Through Windows with Low-Emitting Coatings

Abstract

The thermal performance of a double glazed window with a low emitting coating is studied. Three types ot coatings are considered: single noble metal- films ; noble metal-based triple-layers ZnS/M/ZnS; and sprayed SnO₂-films. The quantities calculated are the total heat-flow, the U₁-value, and the pane- temperatures. Calculations are made both tor night-time and for daytime with varying solar radiation-intensity. Different semi-empirical expressions tor the convective transter give essentially the same results. Particular attention is given to the net effect of absorption in the coating. It is found that with the coating on the inner pane, about 70 percent of the absorbed solar energy is effectively transferred as heat into the room. In an overall comparison with strong insolation considered, the SnO₂-films show the best properties even if the triple-layers have higher solar transmission.