CO2 Heat Pump Water Heater: System Design and Experimental Study

A performance testing experiment platform of heat pump water heater of CO2 trans-critical cycle whose evaporator and gas cooler are both sleeve type heat exchanger has been designed and then constructed. CO2 refrigerant charge amount of the system is 1.23 kg. System performance has been researched by adjusting the degree of opening of the expansion valve and controlling the flow of water of the gas cooler. The results show that: The system can provide hot water of 65 degrees when its cop is 3.2. And hot water of above 80 degrees can be obtained when system's cop is above 2.0. The water flow of the gas cooler has the greatest impact on the cop of the system, the temperature of water out of the gas cooler, and the exhaust pressure of the system. With highly efficient heat exchanger, the temperature of water out of the gas cooler could be increased while compressor discharge temperature is remained the same. So when the system provides high temperature water, it could run in higher cop.