Optimum insulation thickness of residential roof with respect to solar-air degree-hours in hot summer and cold winter zone of china

Abstract

Thermal protection of building envelope is one of the most effective ways for building energy conservation. In this study, the determination of optimum insulation thickness for residential roof with different surface colors is studied based on life cycle cost analysis and solar-air degree-hours in four typical cities of hot summer and cold winter zone of China. Four insulation materials including expanded polystyrene, extruded polystyrene, foamed polyurethane and foamed polyvinyl chloride are analyzed. The solar-air degree-hours are calculated considering night time operation and 24-h operation of the cooling and heating equipments. Life cycle total costs (LCT), life cycle savings (LCS) and payback period resulting from the use of optimum insulation thickness are calculated. Depending on different cities, insulation materials and roof surface colors, optimum insulation thicknesses of a typical roof vary from 0.065 to 0.187 m and payback periods vary from 0.9 to 2.3 years for 24-h operation of cooling and heating equipments; optimum insulation thicknesses are between 0.051 and 0.149 m and the payback periods are between 1.1 and 2.8 years for night time operation. At last, the effects of present worth factor, thermal resistance and climate on the optimum thicknesses are studied which is very useful for practical use to estimate the optimum thickness of insulation material.