Determination of optimum insulation thickness for building walls with moisture transfer in hot summer and cold winter zone of China

The buildings are exposed to the hot-humid climate with high temperature and humidity in hot summer and cold winter zone of China. Moisture transfer and accumulation within exterior walls have notable effect on the cooling and heating transmission load. Finally, it will influence the thickness of insulation. In this paper, a coupled heat and moisture transfer model which considers the effect of the moisture transfer on heat transfer is presented to calculate the cooling and heating transmission load. Then, the optimum insulation thickness of exterior walls is determined by using the P1-P2 economic model. Three representative cities, Changsha, Chengdu and Shaoguan, are chosen as the sample cites. The results show that the optimum thickness of extruded polystyrene (XPS) is between 0.053 and 0.069 m and the optimum thickness of expanded polystyrene (EPS) is between 0.081 and 0.105 m. The maximum lifecycle saving varies from 16.60 to 28.50 $/m2 and the payback period varies from 1.89 to 2.56 years. EPS is more economical than XPS as insulation because of its lower lifecycle total cost. The comparisons are made between the results based on the coupled heat and moisture transfer model and the transient heat transfer model without considering the influence of moisture transfer.