Experimental Study on Characteristics of Triplex Loop Heat Pump for Exhaust Air Heat Recovery in Winter

Ventilation heat recovery is an important way to effectively reducing energy consumption of buildings. To improve the system performance of a heat pump heat recovery system under large temperature difference conditions in winter, a triplex loop heat pump system was proposed to replace single loop heat pump system under the same working conditions. A prototype, which contained three independent heat pump cycles was made. In the case where the indoor temperature was constant at 20℃ and outdoor temperature dropped from 15℃ to -20℃, the fresh air treatment process, the system pressure ratio, the circulation mass flow rate, the heating capacity and the system COP of the heat recovery system were fully tested and analyzed. Results show that the mass flow rate and the pressure ratio of the triplex loop heat recovery system decrease with the decrease of outdoor temperature but still higher than that of the traditional system, and the heating capacity and COP increase with the decrease of outdoor temperature. Under the experimental conditions, the COP of the triplex loop system has an advantage over the traditional heat pump system. When the outdoor temperature is -20℃, the heating capacity increases by 12.43%, and the COP of the system increases by 23.1%. The performance of the triplex loop heat pump heat recovery system is good in winter. In most cases, the system performance is better than that of the traditional single loop heat pump heat recovery system.