Experimental Study Of Carbon Dioxide Heat Pump Water Heater

With the improvement of people's living quality and widespread application of heating equipment, heat pump water heaters using R22, R134a or other substances as refrigerants are used more and more extensively for people's growing demand for hot water. R22 is not only hazardous to the ozone layer, but also intensifies the greenhouse effect. R134a is not harmful to the ozone layer, but it is a kind of greenhouse gas. In addition, with increasing emphasis on environmental issues, employing eco-friendly refrigerant as the working fluid of the heat pump system has increasingly become the focus of researchers all over the world. Because of the advantages of wider temperature range of supplying hot water, capability of providing high temperature hot water, high coefficient of performance and using eco-friendly refrigerant, CO2 heat pump has become the hot spot of scholars.In this dissertation, CO2 heat pump water heater test rig is designed and established, and experimental research of CO2 heat pump water heater system performance has been done. The main studies have been conducted as follows:(1) Based on the heat transfer research achievements on supercritical and two-phase flow of CO2, the evaporator and gas-cooler in the test rig are designed and selected.(2) The control cabinet, heat sink and heat source water pumps, electric heating water tanks and other parts of the experimental rig were designed.(3) The CO2 heat pump water heater test rig is built. Under the given temperature of heat sink water outlet temperature, the effect of variation of higher pressure and evaporating temperature on system performance and heating capacity are studied. The effects of variation of gas-cooler CO2-side outlet temperature, evaporating temperature, degree of superheat on optimal high pressure as well as system performance and heating capacity under the optimal high pressure are studiedThe experimental data show that (1) under the condition of heat sink water outlet temperature of 45 or 65℃and certain high pressure, coefficient of performance of CO2 heat pump water heater is directly proportional to the evaporating temperature, except that under the condition of 65℃outlet temperature of heat sink water and high pressure of 9.5MPa. Under the conditions of certain outlet temperature of heat sink water and evaporating temperature, with the high pressure rising, the system heating capacity increases first and then decreases, so the coefficient of performance has a maximum value, of which the range is from 1.69 to 3.45. (2) Under the conditions of certain gas-cooler CO2-side outlet temperature and evaporating temperature, CO2 heat pump water heater has a maximum coefficient of performance, of which the range is from 1.5~4.92. The pressure which corresponds to the maximum COPh is called optimal high pressure. The range of optimal high pressure is from 8.16MPa~10.61MPa. Gas-cooler CO2 side outlet temperature has a significant affect on the optimal pressure, while evaporating temperature and degree of superheat impact on the optimal pressure weakly.