Thermal Analysis of Complex Glazing

The use of bidirectional scattering distribution function incorporated in a transient systems simulation program, allows engineers to accurately determine glazing surface temperatures for complex glazing assemblies in architecturally ambitious projects. Understanding the thermal behavior of complex glazing assemblies is increasingly critical to high-performance facades - for structural, condensation and occupant comfort considerations. Bidirectional scattering distribution functions account for the way that radiation with different angles of incidence are transmitted through and reflected from glazing. To date these functions have been more widely applied in daylight analysis and not in thermal analysis, partially due to a lack of thermal analysis tools utilizing these functions. Newly included bidirectional scattering distribution function features in a transient systems simulation software allow a more precise accounting for heat flow through glazing assemblies, including air gap temperatures and glass surface temperatures. This newly extended capability was used to investigate the thermal stress in glazing assemblies for two projects: Grace Farms in New Canaan, Connecticut (built and occupied) and the new Little Caesars’ corporate headquarters in Detroit, Michigan (under construction), both located in humid continental climates. These projects, both using glazing innovatively, required additional structural analysis of the glass due to differential thermal loading (Grace Farms with ~3000 linear feet of 12-14 feet tall curved double-glazed insulated glass units and the Little Caesars’ headquarters with a highly-articulated curtain wall facade). In the case of Little Caesars’ project, the calculation allowed for designers to identify dangerous levels of thermally induced stress in the assembly design. These case studies represent two of the first real-world examples of this methodology.