JAUE2024-004: Radiation Characteristics of Double Roofing with Air Passage

Abstract

This paper presents computational fluid dynamics (CFD) results that clarify how the radiation characteristics of the shielding material of a double roof with an air passage affect the heat-shielding performance. The double roof comprises the building’s existing roof with solar shielding material a certain distance from it, and this structure is expected to dissipate most of the received solar radiation to the outside via ventilation between the roof surface and the solar-radiation shielding material. Unsteady CFD analysis shows that the amount of heat transfer from ceiling to room during the day when using a shielding material with high solar reflectance on the top surface and low emissivity on the lower surface is reduced by approximately 80% compared to the standard radiation characteristic specifications. When this structure is applied to a concrete roof, the heat transfer from ceiling to room at night is reduced almost completely. Also, this structure has a heat-shielding performance that exceeds that of a double roof with external heat insulation.