Design of an Air Source Heat Pump System with “One Energy for Multiple Uses” and Numerical Simulation of Airflow Field in Solar Greenhouses

Abstract

To address the issues of airflow stagnation, uneven temperature and humidity distribution, high risk of disease outbreak, and the urgent demand for energy-saving heating in small- and medium-size solar greenhouses under closed winter operation in cold and arid regions of northern China, we constructed a multienergy complementary system coupling heat copper tube, double-vacuum solar collectors with an air–electric hybrid air source heat pump. Leveraging the operating characteristics of the air source heat pump, the system achieves “one energy for multiple uses,” covering energy storage heating, ventilation cooling, and indoor airflow circulation. In our study, Fluent software was adopted to perform numerical simulations on different air outlet schemes of the exhaust duct, and the optimal pipeline scheme was selected, with air volume uniformity as the evaluation index. A simplified greenhouse model was established to analyze the airflow field distribution characteristics in the crop canopy area. Meanwhile, combined with the heating and air exchange performance of the unit, greenhouse ventilation regulation strategies under different weather conditions were formulated. Our results show that the four-outlet scheme delivers more balanced air volume distribution in the pipeline, and its air supply uniformity better matches the spatial characteristics of the greenhouse. The wind speed at a crop canopy height of 0.2 to 1.0 m inside the greenhouse stabilizes at 0.32 to 0.56 m·s –1 , which can effectively break the air stagnation state and improve the crop growth microenvironment without additional circulating fans. The system can simultaneously realize indoor airflow circulation and moderate cooling while heating and storing energy, reducing greenhouse operation costs and providing a technical reference for energy-saving environmental regulation of small- and medium-size solar greenhouses in northern China.