Thermally Adaptive Building Coverings: Theory and Application

The paper begins with a brief overview of historical building coverings. Thermadapt™ thermally adaptive buildings are introduced as a completely new class of shingles, siding and roofing. These elements physically change shape in response to thermal loading. In hot weather with high solar loading, the panels curl up and away from the building. As the temperature cools and the sun sets, the Thermadapt™ elements lie close to the building. In cool temperatures, the elements lie flat agains the building transferring solar energy. In extremely cold temperatures, high convexity inherently forms in the elements, forming a pocket of trapped dead air which forms a highly effective layer of insulation. Thermadapt™ elements are analytically modeled using Classical Laminated Plate Theory (CLPT). Although Thermadapt™ elements may use materials like shape memory alloys, cost concerns drive the use of coefficient of thermal expansion mismatch as the basic driving mechanism. A series of experiments were performed on a variety of Thermadapt™ elements using high CTE mismatch pairs of structural materials including graphite-epoxy and aluminum and Invar and aluminum pairings. Analytical estimates are shown to predict the performance of the Thermadapt™ panels with great accuracy with curvature levels measured and predicted in excess of 5 deg/m/°C. Analytical predictions using CLPT employed a lateral constraint, driving lateral curvature, κ_y, to zero by the use of stiff lateral constraint mechanisms like edge rolls and lateral corrugations. This constraint was shown to increase deflections by roughly 33% over the unconstrained elements which were simply allowed to encounter equal curvatures in x and y directions, or “doming.”