Experimental study on effects of compressor speed on a heat pump dryer system with auxiliary solar source

A novel heat pump drying system with auxiliary solar source and ejector using a variable speed compressor has been experimentally investigated. The influences of compressor speed on the performances of novel system were comprehensively evaluated and compared to the basic heat pump drying system. Moreover, the relationship between the compressor speed and the drying temperature under different solar radiation intensity was clarified. The experimental results indicated that the novel system achieved the higher heating capacity and drying temperature because of the input solar energy. However, the excessive heat input to the drying system also would increase the electrical consumption. To solve this problem, the novel system using a variable speed compressor could obtain the same drying temperature as the basic system at the lower compressor speed. When drying at the same temperature of 70 °C, compared to basic system, the novel system using a variable speed compressor improved the moisture extraction rate by 6.8 %–22.4 %, the specific moisture extraction rate by 23.7 %–31.4 %, and the COP by 26.5 %–42.3 %. The results could provide the guidance for combining the variable speed compressor and the heat pump drying system with auxiliary solar source.