Thermal Performance Impacts of Center-of-Glass Deflections in Installed Insulating Glazing Units

TitleThermal Performance Impacts of Center-of-Glass Deflections in Installed Insulating Glazing Units
Publication TypeJournal Article
LBNL Report NumberLBNL-5800E
Year of Publication2012
AuthorsHart, Robert, Howdy Goudey, Dariush K. Arasteh, and Dragan C. Curcija
JournalEnergy and Buildings
Volume54
IssueNovember 2012
Pagination453-460
Date Published11/2012
Keywordsconcave, convex, deflection, field test, gap, insulating glass unit, thermal performance, thermal transmittance, u-factor
Abstract

This study examines the thermal performance impact of center-of-glass (COG) deflections in double- and triple-pane insulating glass units (IGUs) installed at several locations throughout the US. Deflection was measured during summer and winter temperatures; the results show that outdoor temperature variations can be represented a linear change in COG gap width in double- and triple-pane IGUs within the temperature ranges measured. However, the summer-winter temperature-induced deflection is similar in magnitude to the observed spread in COG deflection of similar units at the same temperature, which suggests that factors other than temperature are of equal importance in determining the in-situ deflection of windows. The effect of deflection on thermal performance depends on the IGU's designed gap. Units constructed with smaller-than-optimal gaps often exhibit significant U-factor change due to temperature-induced reduction in gap width. This effect is particularly problematic in high-performance triple glazing where small gap dimension changes can have a large impact on performance.

DOI10.1016/j.enbuild.2012.06.026
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PDF1.65 MB