A model for analyzing the thermal performance of roof configurations with flat inclined surfaces

Abstract

The development of a thermal model, followed by a generalized computational tool that analyses thermal performance of roofs with four inclined surfaces and a ceiling by considering dynamic environmental and operating conditions, changes of roof geometry and materials is presented here. Roof elements are analyzed based on finite-volume method with implicit formulation. View factors of roof enclosures are calculated numerically. Experimental results, obtained for six actual building roofs under tropical climatic conditions of Sri Lanka, indicated that the thermal model is capable of replicating the actual temperature profiles with an average accuracy of 1.1 °C. Ceiling temperature of common roofs were found to be 10 °C above the ambient temperature, which could even rise up to15 °C in hot days. The model was successfully used to compare roofs and quantify the thermal effects of different parameters. For instance, changes in geometrical parameters led ceiling temperature to change by 5 °C, highlighting the importance of roof geometry. Out of the widely used three roofing materials in Sri Lanka, clay tile roofing has showed the best thermal performance. Compared to clay tiles, asbestos and steel roofing can have a maximum ceiling temperature rise of 4 °C and 6 °C, respectively.