Cool Skins: Materials and Assemblies for Ventilated Building Envelopes in Warm Climates

Vertical building skins account for a significant amount of heat transfer from solar gain in the cooling season, especially in multifloor, envelope load-dominated buildings in sunny climates. While the performance of glazing with respect to solar radiation is often given the greatest emphasis, the behavior of the opaque building envelope is also an important factor in cooling season performance. Conventionally, buildings approach this problem in the envelope using just insulation. Ventilated cladding systems can improve the performance of lightweight assemblies in the cooling season, though ventilated cladding is a strategy more widely associated with moisture evacuation. Using mockups and CFD simulation, the author has observed heat transfer rates reduced by over 40 percent by ventilating the building cladding to the exterior. Earlier published findings from the author suggest that the dynamic thermal behavior of these ventilated skins is complex and may be best optimized by using heat-rejecting materials and open joints, countering prevailing research on the subject asserting that only the parameters of the air channel are the critical values for optimization. This paper presents a new phase of inquiry that further characterizes the thermal behavior of ventilated building skins, with special emphasis on the role of radiation, cladding equilibrium temperature, and behavior of the cladding as an assembly with continuous external insulation.

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