Outdoor air state that may cause moisture condensation in membrane-type total heat exchangers using different membrane materials

Total heat exchanger (THX) is an air-to-air heat exchanger with a heat/moisture exchanging core made of water vapor permeable membrane, it is used to reduce the building energy consumption by recovering both heat and moisture from ventilation air. In hot and humid climate, the membrane surface may get a temperature below the dew point of supply outdoor air, causing moisture condensation at the membrane surface, which may degrade the exchanger performance and increase the health risk. In this research, a mathematical model is built to describe the heat and moisture transfer in the core of a THX, the effects of membrane properties on moisture condensation are analyzed, and the critical outdoor air states for occurrence of the moisture condensation are calculated. The results show that large membrane adsorption constant and large maximum moisture uptake may restrain the moisture condensation, which occurs more easily at the intersection of the supply and exhaust airstreams. The optimal membrane properties are recommended based on a comprehensive consideration of the safety and economy.