Theoretical Analysis And Experimental Research On CO₂ Heat Pump Water Heater

In this thesis, the theoretical analysis, computer simulation and experimental study have been completed about natural refrigerant CO₂ as work fluid in heat pump water heater system.Based on the characteristic of CO₂ transcritical cycle, the advantage of CO₂ is compared with common refrigerant which used in heat pump water heater. Through the analysis of optimal high pressure in transcritial cycle system, it is concluded that there are two objective functions in the operating heat pump water heater system: one is COP of system; the other is discharge temperature of compressor. The influence of based parameters on COP and discharge temperature is analyzed, and it is confirmed that there are many measures which can improve the COP of system, such as increasing the heat exchange effect in evaporator and gas cooler, using the high efficient compressor, and using inner heat exchanger to increase the discharge temperature of compressor.The model of double pipe gas cooler is founded and the simulative calculation is completed using the subsection method. The calculated results show that increasing the mass flux and decreasing the diameter of tube can both increase the CO₂ and water heat exchange coefficient. As we know, these two parameters impact to the pressure drop, but this impact is small influence on the COP of CO₂ heat pump water heater system.The CO₂ heat pump water heater system is built in the laboratory. The components of system, the research goal, content and experimental process are explained in this paper. The system is tested in calorimeter at different seasonal environmental temperature and different water flux. The results show that the CO₂ heat pump water heater system can operate smoothly in different seasonal temperature and gain the high temperature water, especially in summer experimental temperature, when the system gain 65℃water, the COP is above 3.45. If the cooling quantity can also be used, the COP will reach 5.9, so the CO₂ air conditioner water heater can save much when used in summer.