Annual performance analysis of heat pump drying system with waste heat recovery

Abstract

Recently, heat pump drying with heat recovery is popular in agricultural products for its high efficiency, fine product quality, and low energy consumption. However, while the heat pump drying performance depends on the ambient conditions, especially when operating continuously throughout the year, little work has been done on the long-term performance evaluation of heat pump drying. Therefore, a meteorological data model is introduced into the mathematical model of a heat pump drying system with waste heat recovery in order to study the annual performance and analyze the total yearly energy consumption, including the effects of the set temperature, the ambient temperature, and the relative humidity on the amount of waste heat recovered, the power consumption, the coefficient of performance, and the specific moisture extraction ratio of the system. The results show that the utilization of outdoor fresh air by the heat pump drying/waste heat recovery system during continuous operation depends on the moisture differences between the air supplied to the drying oven and the outdoor air. At the three set temperatures of 50, 55, and 60 °C, the ratio of annual waste heat recovery to total heat requirement of the heat pump drying system is 57.2, 56.5, and 55.7%, respectively. This reduces the power consumption by 58.2, 57.8 and 57.1%, respectively. Due to the availability of fresh air, the specific moisture extraction ratio is higher between September and June than that in July to August. The maximum value is more than 3.0 in early April when the temperature is relatively high and the humidity is low. The perspective for annual performance analysis in this study helps to further elucidate the energy consumption of heat pump drying, and to provide guidelines for its operation control and design.