Study of a water-source CO2 heat pump for residential use: experimental discharge pressure control and performance analysis

Abstract

The heat pumps with the refrigerant of carbon dioxide (CO2), i.e., CO2 heat pumps, have the merits of low price and environmentally friendliness in comparison with those with traditional refrigerants, e.g., hydrochlorofluorocarbons and chlorofluorocarbons. Current studies mainly focused on the air-source CO2 heat pumps, while investigations about the CO2 heat pumps gaining heat or cold energy from different mediums, e.g., water, are lacking. In addition, although few studies presented the investigations on the discharge pressure of the CO2 heat pumps (e.g., investigations of optimal discharge pressure), how to realize the effective discharge pressure control in the experimental conditions is still lacking. To remedy these knowledge gaps, this study presented an experimental investigation of a water-source CO2 heat pump for residential use. A PI controller was used to maintain the fixed discharge pressure by adjusting the opening of the electronic expansion valve. The dynamic performance of the CO2 heat pump in the typical discharge pressure of 7,200 to 8,400 kPa were analyzed. The results indicated that the method of using the PI controller to adjust the opening of the electronic expansion valve could effectively maintain the desired discharge pressure of the CO2 heat pump in the experimental conditions.