Ya Yuan

Heat pump drying system is prospect technology with high efficiency and energy saving. Stable and efficient operation of heat pump drying systems in cold climate regions is achieved using a separate heat recovery room, which is designed to recover the heat in the exhaust air. Using a separate heat recovery room aims to maintain stable operation through switching between enclosed and partial air-loop modes. This paper analyzes the drying parameters to verify the stability of system, compares the running modes, and evaluate the economy of the dryer. It is found that setting a separate heat recovery room can achieve a higher material uniformity, and the air parameters are less affected by surroundings. Moreover, modes need to be adjusted according to the drying parameters and surroundings. Meanwhile, the proposed system has a great advantage in reducing the exergy loss of the heat exchanger, which can reduce operating costs.

This study presents the development and evaluation of a novel partially open-loop heat pump dryer with a unit-room (HPDU). The unit-room was designed to enable the ambient air to be mixed with the return air, thereby reducing the influence of the ambient air on the system performance, while maintaining a high system thermal efficiency. A modelling system for the HPDU was developed and validated based on a real-scale experimental study. By using the modelling system, the system characteristics under different ambient conditions and bypass factors were analyzed. The energy benefit of the proposed HPDU was quantified through a comparative study with a closed-loop heat pump dryer (CHPD). It is evident that a maximal specific moisture extraction rate (SMER) and a minimal total energy consumption (TEC) existed when changing the bypass factor of the HPDU under certain ambient temperatures. Compared to the CHPD, the coefficient of performance (COP) of the HPDU increased by up to 39.56%, presenting a significant energy benefit for the application of HPDU.