Abstract:In order to explore an energy-efficient thermal environment control model in greenhouse, based on heat pump technology, a new type of air-soil dual-source heat pump system matched with the greenhouse model was designed and built, and the system performance was also tested. This system was compounded of air source heat pump and soil source heat pump, and adopted the plate heat exchanger in series form. The air-soil dual-source heat pump system had four kinds of heating modes, including air source mode with single plate heat exchanger, air source mode with double plates heat exchanger, soil source mode with single plate heat exchanger and soil source mode with double plates heat exchanger. These working modes can be converted by controlling the on-off of the electromagnetic valve. The soil source heat pump mode can solve the adaptability problem of air source heat pump under low temperature condition, while the air source heat pump mode can alleviate the problem of imbalance of the acquisition and release of the soil source heat pump. In the winter and spring test period, the COP (coefficient of performance) and temperature rise rate of the heat pump system in air source mode with single and double plates heat exchanger were tested by heating the water in the heat insulating water tank. The operation results in spring were better than that in winter. In spring, the COP of the heat pump system in single and double plates air source mode were 2.1 and 3.1, respectively, and the COP of the heat pump system in single and double plate soil source mode were 2.2 and 2.3, respectively. The energy-saving effect of air source mode with double plates heat exchanger was the most significant, the energy-saving rate was up to 50.4%. During the winter test period, the air source mode with double plates heat exchanger could raise the temperature in the greenhouse model in the typical sunny days. The indoor temperature was higher than the outdoor temperature about 15.7℃ on average. According to the results, the performance of the double plate heat exchanger was both better than that of the single plate heat exchanger during the winter and spring. The results also showed that both the amount of heating medium and system pressure can affect the effect of the dual-source heat pump system. In conclusion, this air-soil dual-source heat pump system can make use of air energy and geothermal energy efficiently to realize the energy conservation of solar greenhouse in winter.
