Study On Medium-High Temperature Heat Pump Water Heaters

Heat pump water heaters have developed rapidly in these years with their advantages of energy saving, environment friendly, safety and reliability, etc, and are suitable for preparing moderate or high temperature hot water in food, biological and chemical industries. In this paper, three kinds of heat pump water heaters are discussed. Their structures, regulating methods, techno-economic characteristics, advantages and disadvantages are introduced systematically.The structures and performance of medium-high temperature heat pump water heaters are theoretically analyzed. According to the space supplied by users, different structures are given with different technical and economic characteristics. Relations of hot water temperature, hot water supply ways and operating modes to the performance of heat pump water heaters are given. In addition, the energy consumption, cost of producing hot water and environment load are calculated and compared between electrical heat pump water heaters and gas heat pump water heaters.Based on theoretical study, an experimental medium-high temperature heat pump water heater is set up. Three kinds of heat pump refrigerants (KD01, KD02, KD03) are used in experimental study. It shows that COP of heat pump reduces rapidly with the increase of hot water temperature. With the refrigerant KD01and KD02, when the evaporating temperature is15℃, the COP declines by45%when hot water temperature increases from40℃to60℃. With the refrigerant KD03, when the evaporating temperature is35℃, the COP declines by47%when hot water temperature increases from60℃to80℃. In addition, the efficiency of heat pump compressor will be lower than its normal value when the medium-high temperature heat pump water heater runs under high temperatures and pressures, and the heat loss of the compressor and pipe lines will also result in the decrease of COP.