Thermal behaviour of a building envelope in a hot arid climate

Abstract

Abstract Conservation of energy and improved thermal comfort can be achieved through a proper design of the building envelope. Thicknesses, thermal conductance and solar absorbance of exterior surfaces of a building have a profound effect on indoor thermal environment. This is more so in a hot arid climate characterized by a large diurnal temperature variation and a high solar insolation. The present study investigates the effect of these building parameters on the peak indoor environmental temperature, its time of occurrence and inside temperature swing. For this study, a mathematical model is developed from energy balance equations for important building components. The model uses time lag and decrement factor concepts for conductive heat transfer through opaque exterior surfaces to simulate transient behaviour of the building. After validating, the model is run on the computer. Results of the simulations show that wall thickness is the important factor affecting the thermal behaviour of buildings in a hot dry climate while thermal conductance is comparatively less important. The relative effect of the solar absorbance of exterior surfaces stands somewhere between these two factors. The optimum ranges of these parameters for the climate in Iraq, as predicted by the model are: 1. (a) Exterior wall thickness 24–36 cm. 2. (b) Exterior surface solar absorbance 0.3–0.75. 3. (c) Wall thermal conductance 1–2 Wm −2 C −1 .