Glazing for Energy Efficient Buildings: The Almost Forgotten Role of Angular-Dependent Solar Transmittance
(Room Room 104-A)
29 Apr 19
5:20 PM
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5:40 PM
Tracks:
Coatings for Energy Conversion and Related Processes
Modern buildings use glazing with multiple glass panes and advanced surface coatings to create energy efficiency and indoor comfort. Spectral selectivity is essential, and coatings should have sufficient transmittance for visible light and high reflectance for thermal-infrared radiation to avoid radiative heat loss between adjacent glass panes. Coatings of this type have been widely used for decades. Another important property for glazing, which has become available only recently, is temporal variability implying that the transmittance of solar energy and visible light is regulated via multilayer constructions including electrochromic coatings so that air conditioning is minimized and glare is avoided. A third essential aspect for glazing is that solar irradiation often impinges at strongly off-normal angles, which necessitates that the glazing’s angular dependence be included in assessments of energy efficiency. It is therefore not adequate to characterize glazing with light at normal incidence—as is generally done. The problem with current practice, and standards, becomes aggravated as the number of individual layers in a coating is increased. This paper identifies and specifies the importance of angular-dependent solar transmittance for glazing and presents optical data for glass panes with multilayer coatings as well as for multi-pane constructions incorporating such coatings.