Experimental study and operation optimization of a parallel-loop heat pump for exhaust air recovery in residential buildings

The indoor space of residential building is limited, especially in building retrofit, to improve the indoor space utilization and the performance of exhaust air heat recovery system, a novel dual-cylinder rotary compressor with independent suction and discharge ports was designed to drive an inverter parallel-loop exhaust air heat pump. Through the experiments and analyzing the parallel-loop exhaust air heat pump system working characteristics under variable compressor frequency and different fresh air volume flow rate, the optimized method is proposed and verified experimentally. Finally, the annual energy efficient operation plan was proposed, and the seasonal performance factor and seasonal average input power under this operation plan in three typical countries/organization were calculated. Results show that the system COP can be greatly improved by applying a mixed air supply method during winter. When the fresh-air-to-return-air ratio is 1:1 and the outdoor temperature is -5 degrees C, the system COP reached 10.18, which is the highest comparing with the related studies. In summer, the system COP is increased by increasing the ventilation volume flow rate. When the operation of the parallel-loop exhaust air heat pump system follows the energy efficient operation plan to ensure the temperature effectiveness over 100% and the outdoor working condition complies with GB 21455-2013, the heating season performance factor, heating season average input power, cooling season performance factor, and cooling season average input power are 7.22, 0.6909 kW, 2.83, and 0.8167 kW, respectively. The work would provide guidance for the development of exhaust air heat recovery system in residential building.