Experimental and theoretical analysis of the optimal high pressure and peak performance coefficient in transcritical CO2 heat pump

Based on the high performance and the environmentally friendly characteristics, the transcritical CO2 heat pump has attracted much attention in last few decades. The high-pressure control is one of the essential factors determining the coefficient of performance due to the large pressure changes in the transcritical CO2 heat pump system. In this work, the contribution rates of different factors to the optimal high pressure and the peak performance coefficient were analyzed by the method of the analysis of variance. Then, the influences of compressor frequency, inlet water flow rate and inlet water temperature on the optimal high pressure and the peak performance coefficient were experimentally investigated on the basis of theoretical analysis. Finally, a novel discharge pressure deviation was proposed to calculate the optimal high pressure, and the occurrence regularity of optimal high pressure was investigated. The results indicated that the gas cooler outlet temperature was the main parameter influencing on the optimal high pressure, peak performance coefficient and discharge pressure deviation. The calculated discharge pressure deviation can seek the optimal high pressure with the average error of 0.57% and the performance coefficient loss of 0.34%. Additionally, the optimal discharge pressure of the experiment was likely to appear in the descending stage of the gas cooler outlet temperature.

Automated summary

This study investigates the impact of high-pressure control on performance in transcritical CO2 heat pump systems, and examines the effects of compressor frequency, inlet water flow rate, and inlet water temperature on optimal high pressure and performance coefficient through experimental and theoretical analysis. A new method for calculating discharge pressure deviation is proposed, and the occurrence pattern of optimal high pressure is investigated.