Computational investigation of the impact of glass flexure on thermal efficiency of double-pane windows

Windows contribute significantly to the energy efficiency of a building because a considerable amount of energy can potentially be lost through windows. Double-pane windows are particularly efficient at reducing heat loss, primarily via the thermal insulation afforded by the insulating gas filled inside the gap between two panes of glass. However, glass flexure and deformation during window assembly and cold weather can substantially alter the effective thermal resistance of double-pane windows. We systematically consider this (inward and outward) flexure effect on thermal performance in the current work. A validated finite volume method with k- ω SST turbulence model is utilized to perform 3D simulations of a commercially available double-pane window. High-performance computing-based simulations are performed to unravel the impact of different amounts of flexure on effective heat loss. We find that the total heat loss increases as the degree of inward flexure increases, with the case of maximum inward flexure resulting in ∼ 15% more heat loss compared to the baseline no-flexure case. On the other hand, outward flexure of the glass does not result in any appreciable variation in heat loss. This suggests pre-flexure as a viable means of ensuring consistent performance under wide weather conditions. Finally, we develop a quasi-2D approach that approximates the very expensive 3D simulations presented here. The quasi-2D method essentially integrates a series of 2D slices in a 3D case to estimate the total heat loss across that 3D case. This decomposition of a 3D window simulation into several 2D simulations substantially reduces total computation efforts and produces reliable results for the very large aspect ratio exhibited by the double-pane window geometry.