Moisture Transfer In Building Envelopes Effects On Energy Consumption

Moisture transfer in building envelope is important not only for the characterization of behavior in connection with durability, waterproofing, degradation of appearance and thermal performance, but also for improving the building energy efficiency and indoor comfort. However, in most building energy analysis, the calculation of heat conduction through walls usually neglects the transport and storage of moisture in porous building materials and the interaction between hygrothermal transfer and air inside the building. With the fast development of computing technology, more detailed whole building hygrothermal simulation becomes reality.This paper carried out a field measurement survey on indoor thermal environment and energy consumption of residential buildings in Nanjing. Based on this investigation, a detailed model for predicting moisture effects on building energy consumption and indoor comfort is presented. Non-isothermal moisture sorption and desorption processes in building envelope are calculated. The model is applied to investigate the moisture transfer effect on indoor air humidity and building energy consumption in the Middle & Lower Yangtze Region in Southeast China, where the monthly average outdoor Relative Humidity is higher than 75%. This region is the most developed area in China (including Shanghai, Nanjing, Hangzhou etc.) and has a fast growth in energy demand in building sector. The paper presents an analysis and comparison of heating/cooling energy consumption with and without considering the moisture transfer through the building envelope. Moreover, actual application in typical residential buildings proved that this method has certain accuracy.The results show that not accounting for hygrothermal effects in modeling will result in overestimation of energy costs for hot and humid climates and possible over-sizing of plants, leading to inefficient operation.