Experimental Study of Heat Transfer Through Windows Exposed to a Radiant Panel Heater

Abstract

Structure hardening is a key strategy to help mitigate building destruction during wildland-urban interface fires. Windows represent an important vulnerability for structure failure by allowing heat transfer to interior combustibles, and in cases of mechanical failure, an entry point for flames and/or embers. The purpose of this study is to characterize heat transfer through windows with various common construction variables (plain (annealed) versus tempered glass, single- versus double-pane, low-emissivity coating versus no coating, and air-filled versus argon-filled pane gap). Small-scale experiments were performed with 23 cm by 23 cm windows exposed to a radiant panel producing centerpoint incident heat fluxes of 10 kW/m2, 20 kW/m2, 30 kW/m2, 40 kW/m2, and 50 kW/m2. Total heat flux was measured 5.1 cm behind the window glass. Times of pane cracking and other failure events were recorded. Double-pane designs reduced heat transfer through a window more than the single-pane design (measured 13% to 43% and 39% to 60% of the incident heat flux, respectively). Heat transfer was further reduced when a low-emissivity coating was present (measured 5 to 14% of the incident heat flux). The differences in measured heat flux behind plain glass versus tempered glass windows and air-filled versus argon-filled windows were not statistically significant. Tempered glass performed better than plain glass, and double-pane argon-filled windows consistently survived longer than double-pane air-filled windows. In some cases, heat fluxes measured behind the windows surpassed the critical heat flux required for ignition of some common household combustibles.