Simulation study on performance of a solar assisted heat pump drying system

Solar assisted heat pump drying system has been proposed to improve the efficiency of energy using for drying process due to drying is an energy intensive process and solar drying is deeply influenced by local weather compared to heat pump drying. In this study, a new solar assisted heat pump dryer has been designed and investigated. The drying system consists of a compressor, evaporator-collector, air condenser, air collector, dryer, blower and dampers. This system can realise three kinds of working modes, including solar drying, heat pump drying and solar assisted heat pump drying, and also can switch operating condition on opening, semi-opening and closing based on heat pump according to the path of drying medium. MATLAB program has been developed to evaluate the performance of the system and the influence of different variables. Results suggest that the entire drying time of the product decreases with the increase of drying air temperature, in addition, The air temperature of each outlet varies little with the ambient temperature and solar radiation when system working with mode of solar assisted heat pump. Coefficient of performance (COP) and the specific moisture extraction rate (SMER) are two main performance indices. With the increase of ambient temperature or solar radiation, the COP slightly decreased, but the SMER increased significantly. The SMER of the system can be improved under certain environmental conditions by adjusting the refrigerant flow ratio of evaporator. Analysis reveals that the drying system with simple structure is sustainable, adaptable and good for high quality product.