Influence of Infrared Radiation of Windowpanes on Indoor Thermal Environment―Emissivity Variation due to Condensation in Heating Period―

Abstract

We examined the influence of condensation on infrared radiation of windows and indoor thermal environments in winter when condensation forms. Two windows, which had high- and low-emissivity (-e) surfaces, were installed in practical-sized rooms. One was a single glazing with an emissivity of ≈0.9 and the other consisted of a low-e film (0.13 on catalogue) retrofitted on single glazing. We measured emissivity of dry and wet window surfaces, as a function of surface temperature. In the practical-sized rooms, we measured air, window-surface, and globe temperatures, and discuss the indoor thermal environment at different atmospheres. The condensation on the windows increased the surface temperature and decreased the globe temperature, whereas it maintained air temperature constant indoors. The variation in these temperatures was explained based on emissivity change due to condensation. We discussed the relationship of indoor comfort with installation of low-e films and occurrence of condensation, using standard effective temperature (SET*).