A preliminary study of the performance enhancement of a dual-mode heat pump using an ejector.

This paper presents a preliminary study on performance enhancement of the cooling and heating CO2 system with energy recovery by a controllable ejector. The effects of the variations of ejector internal geometry, compressor frequency and operating conditions on the performance of an ejector expansion transcritical CO2 system for cooling and heating were investigated experimentally. Experimental results show that the COP of a dual-mode CO2 system can be enhanced by using an ejector expansion device to replace a conventional expansion valve. As ejector motive nozzle throat diameter decreases, heating capacity and heating COP increase. As compressor frequency decreases from 60Hz to 35Hz, the total COP can be increased by up to 98% compared to the conventional cycle with a constant compressor frequency at 60 Hz, although both total cooling and heating capacity drop a little. As outdoor air temperature increases, the total COP decreases while the total capacity changes very slightly. As indoor air temperature increase, the total capacity increases while the total COP change slightly. This study will be helpful for the future study of optimizing the vapor compression cycle systems using an ejector as the expansion device under various operating modes.