Dynamic Thermal Characteristics Research On Cascade Air Source Heat Pump Water Heater With Pcm

Air Source Heat Pump Water Heater (ASHPWH) is kind of the system that air energy is absorbed at evaporator and pumped to storage tank via a Rankine cycle, and then the coil pipe/condenser releases condersing heat of the refrigerant to the water side. Because its save,environmeatal protection,energy-saving and low-carbon,ASHPWH is widely used by more and more people.In recent years, the use of thermal energy storage system with PCM has gained consideral attention, because PCM has high heat storage density and a narrow range of phase change temperature. Combined the cascade heat pump system technology with the thermal energy storage, cascade air source heat pump water heater with PCM system is showed on this paper. The new system uses R134a and R404a as the refrigerant , and then it could be new trend on energy-saving in the air-conditioner industry. Transient temperature variation and heat transfer characteristics approach has been developed for the analysis of thermal storage process and thermal release process according the experiment and the simulation method.Firstly, the theoretically analysis and study is performed, including the principle of operation,the caculation model of the cascade system,the appropriate phase change temperature of PCM,and the appropriate PCM . And then, a method that the cascade heat pump unit functions in single - stage cycle on summer and cascade cycle on winter is developed.In this thesis, an experimental setup for cascade air source heat pump water heater with PCM is improved , and then the systematic testing and analysis of the performances of the heat pump system under different working conditions—7/6℃,15/14℃,20/15℃,38/23℃(dry bulb temperature/wet bulb temperature)are conducted. A large quantity of experimental data has been obained, which provides the fondation data for further improvement research of this heat pump system.In the running process, how the heat transfer transiently from low temperature class to high temperture class, and then to the water and the PCM heat exchanger is dicussed. It is also showed that transient COP and the mean temperature difference from low temperture class to high-stage cycle. Both in thermal storage process and thermal release process, dynamic temperature of the water tank in different position is showed. According the experiment , it comes out that when the water average temperature is 55℃, which its outdoor temperature optimizing control conditions and maximizing energy– saving is almostly 7℃. Considering the same outdoor temperature, it also has only one condenser temperature maximizing energy– saving.Numerical simulation about thermal storage process of the system on the outdoor temperature 7/6℃is also carried out by MATLAB software .Comparing experimental results with theoretical ones, it is demonstrated that the proposed model can be used to describe the running characteristic of such an equipment in the thermal storage process, providing some improvements on the basis of the simulation platform.