Drying and dynamic performance of well-adapted solar assisted heat pump drying system

Abstract A new type of well-adapted solar assisted heat pump drying system (SAHPDS) was put forward to choose and switch more efficient and energy-saving drying mode according to outdoor environment. The drying characteristics of shiitake mushroom, energy consumption level and running characteristics of system under five drying modes were investigated systematically. The drying modes were independent solar drying system (ISDS), independent closed heat pump drying system (ICHPDS), and SAHPDS of closed, open and semi-open modes. The results concluded drying system performed well in each mode. In ISDS, inlet air temperature of drying chamber can reach above 50 °C, heat collection efficiency of solar air collector (SAC) is 0.562 and SMER is 3.56 kg/kWh. In ICHPDS, the average COP is negatively correlated with air temperature and loading capacity, while positively correlated with air speed. In SAHPDS (assisted only by SAC), the average air temperature is 59.17, 62.38 and 60.83 °C in open, closed and semi-open modes at air speed of 3.5 m/s. With the corresponding modes, the heat collection efficiency of SAC was 0.526, 0.223 and 0.434 respectively. The average COP is 3.08, 2.68 and 3.20, which is significantly more energy-saving than ICHPDS mode in order to obtain same air temperature. In the later drying period, it switched to the closed drying mode of SAHPDS (only assisted by solar collector (SC)). In addition, the energy saving rate can reach 37.96% compared with ICHPDS under the same condition. The study provides a guidance and reference for the operation mode switch of SAHPDS with higher energy saving and efficiency.