Optimal spacing for double-skin roofs

Abstract

Double-skin design is known as an effective way to reduce the building's solar heat gain. In this study, inclined parallel plates with upper plate heated by a lighting system are used to simulate double-skin roofs exposed to solar irradiation. Heat transfer experiments were carried out for different inter-plate spacing and different inclined angles. In some of our test runs, a radiant barrier is also installed on top of bottom plate to further cut down the building's heat gain. The Nusselt numbers reduced from our test data are consistently matched with Azevedo and Sparrow's correlation. The optimal inter-plate spacing, when the most heat gain is blocked out, can be directly obtained from our test data which is very close to the sum of both plate's thermal boundary layer thicknesses.