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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 P 1 – P 2 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 $/m 2 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. [ABSTRACT FROM AUTHOR]

The building envelopes are exposed to the hot-humid climate with high humidity in hot summer and cold winter zone (HSCW) of China. The moisture transfer may severely influence the conduction loads through exterior walls. In this paper, a coupled heat and moisture transfer model is developed and validated to investigate the thermal performance of exterior walls. The conduction loads through a typical exterior wall are used to evaluate the effect of moisture transfer on the thermal performance of exterior walls in HSCW zone of China. The results show that the peak cooling and heating loads are overestimated by 2.1–3.9% and 4.2–10.1%, respectively, when ignoring moisture transfer. In cooling season, the sum of the latent load accounts for 14.3–52.2% of the sum of the total load and the yearly latent load accounts for 4.9–6.1% of the yearly total load when considering moisture transfer. The total cooling, heating and the yearly load are underestimated by 9.9–34.4%, 1.7–4.0%, and 5.2–6.8%, respectively, when ignoring moisture transfer. The results indicate that ignoring moisture transfer causes significant discrepancy in predicting the conduction loads. A detailed model considering moisture transfer in building envelope is essential to accurately evaluate the building energy performance in HSCW zone of China. [ABSTRACT FROM AUTHOR]