Experimental investigation on performance of transcritical CO2 heat pump system with ejector under optimum high-side pressure

Since the fixed ejector cannot adjust the optimum high-side pressure, the adjustable ejector is designed and built based on a transcritical CO2 heat pump system model results. The adjustable ejector is subjected to electrical pulses through the stepper motor which drives needle forward or backward movement to change the nozzle throat area for the optimum high-side pressure. Experimental investigation of the transcritical CO2 heat pump cycle with adjustable ejector is presented. The effects of the high-side pressure on the system performance are analyzed. A control strategy for maximum COPh is developed by correlating the CO2 pressure and temperature at the gas cooler exit, yielding the ejector optimum high-side pressure control equation. Experiment results show that there exist maximum values for heating performance coefficient and heat capacity with increasing high-side pressure. The increased high-side pressure has a positive effect on the system performance and outweighs lower ejector efficiencies. The ejector efficiency is mainly distributed within range of 20%–30%.

► The adjustable ejector is designed and built for the transcritical CO2 ejector heat pump system.
► Experimental investigations are performed by varying the motive nozzle throat area to control the high-side pressure.
► The ejector optimum high-side pressure control equation is developed.
►  The ejector efficiency is mainly distributed within range of 20%–30%.
► The ejector high-side pressures for maximum COPh are lower than that for maximum heating capacity.