Performance testing of a heat pump system with auxiliary hot water under different ambient temperatures

Abstract

• Solar-assisted heat pump system with auxiliary hot water was proposed. • Influence of auxiliary system and EEV opening on system performance was studied. • The optimal experimental combination was obtained by orthogonal experiment. In recent decades, solar collector and heat pump combinations have been widely applied to supply heat and hot water, such as in heat supply and power generation for domestic and commercial buildings and relevant applications in the manufacturing and agricultural industries. However, the solar-assisted heat pumps already in extensive use may undergo system performance deterioration in a cold environment. To solve this problem, we designed a heat pump system assisted with hot water where a water medium was used to store energy to assist the operation of the heat pump at low temperatures. Three factors were comprehensively considered: the opening degree of the electronic expansion valve, the temperature of the low-temperature heat source, and the auxiliary hot water temperature. Crossover experiments were designed with three levels for each factor, and 36 groups of experiments were carried out. The results showed that as the auxiliary hot water temperature increased, the heating capacity and the coefficient of performance also increased. Thus, the overall working efficiency of the system improved. According to the orthogonal test, the most important influencing factor of system performance was the auxiliary hot water temperature, followed by the ambient temperature and opening degree of the electronic expansion valve. These results fully demonstrated that the addition of auxiliary hot water could dramatically improve system performance. In addition, optimization of the opening degree of the electronic expansion valve produced different results, indicating that the optimal value ranged from 50%−75%.