A dynamic parameter to describe the thermal response of buildings to radiant heat gains

tThis papers deals with the surface factor, a dynamic parameter that describes the thermal response of awall to a cyclic radiant heat flux absorbed on its inner surface. Despite it was available since the Seventiesin the framework of the admittance procedure, the surface factor has not been fully exploited and, unlikeother dynamic thermal properties, it has been very rarely dealt with in the scientific literature.After a concise presentation of the mathematical background, the paper proposes the calculation of thesurface factor for common single-layered walls, in order to investigate its sensitivity to the thickness andthe thermophysical properties of the slab. Two graphs are presented for an easy and precise determinationof the amplitude and the time shift of the surface factor, as a function of the properties of the material. Theeffect of an insulating layer is also addressed, by varying both its position and thickness. Furthermore,the investigation shows that the values of the film thermal resistance suggested by current Standards arenot always appropriate, and may introduce significant inaccuracy.The results provide very useful information for optimizing the response of a wall to periodic heat fluxesacting on its internal surface.