Theoretical And Experimental Study On Variable Condition Performances Of Instant Heat Pump Water Heater System

Heat pump water heater technology can achieve efficient production of domestic hot water,and accordingly can effectively reduce building operation energy consumption and carbon emissions.The HFCs refrigerants currently widely used in heat pump systems are alternative refrigerants due to their high GWP.However,the search for environmentally friendly alternatives by evaluating their replacement potential has become a hot topic in heat pump technology research.The paper presents a comparative analysis of the performance of R744/R290（12/88）(referred to as M_opt)and R22 direct heat pump water heater systems under variable operating conditions,using the non-azeotropic R744/R290 as the object of study,both theoretically and experimentally.The study and the conclusions drawn are as follows:（1）A comprehensive analysis of the environmental,thermodynamic and transport performances of M_optand R22 shows that while M_optachieves significant environmental benefits over R22,it also exhibits similar standard boiling points,critical temperatures,critical pressures,saturation vapour pressures and higher latent heat of gasification and thermal conductivity under the same conditions,demonstrating the potential of M_optas a direct tank-fill replacement for R22.（2）Based on the established theoretical model of heat pump water heater and the test device of direct heat pump water heater,the influence law of heat sink inlet temperature and heat source inlet temperature on the circulation performance of M_optand R22 system was studied theoretically and experimentally.The results show that the M_optsystem achieves significantly higher experimental heating COP and experimental heating capacity,slightly higher experimental exhaust pressure and significantly lower experimental exhaust temperature at variable heat sink inlet temperature compared to the R22 system.The experimental heating COP and experimental heating capacity of the M_optand R22 systems have very different trends as the inlet temperature of the heat sink changes,while their corresponding experimental exhaust pressure and experimental exhaust temperature have similar trends.As the heat sink inlet temperature changes,the experimental heating COP and experimental heating capacity of the M_opttrend slightly differently from the corresponding theoretical heating COP and theoretical heating capacity,while all other experimental performance parameters have similar trends to the corresponding theoretical results,while the corresponding experimental and theoretical cycle performance parameters of the R22 system have similar trends.Compared to the R22 system,the experimental heating COP and experimental heating capacity of the M_optsystem at variable heat source inlet temperatures were significantly improved for most of the variable heat source inlet temperature conditions,and the M_optsystem exhibited slightly higher experimental exhaust pressure and lower experimental exhaust temperature for the variable heat source inlet temperature conditions studied.As the inlet temperature of the heat source increases,the trends of the experimental heating COP and experimental heat production for both M_optand R22 systems are somewhat different,while the corresponding trends of the experimental exhaust pressure and experimental exhaust temperature tend to be the same.As the inlet temperature of the heat source increases,the experimental heating COP and experimental heating capacity of M_optvary from the corresponding theoretical heating COP and theoretical heating capacity respectively,but all other experimental performance parameters have a similar pattern of variation to the corresponding theoretical results respectively,while the corresponding experimental and theoretical cycle performance parameters of the R22 system are consistent.（3）Based on the theoretical model,a theoretical prediction of the variation pattern of the cycle performance of M_optand R22 systems under variable heat source temperature drop operating conditions was made.Calculations show that under the studied heat source temperature drop conditions,the theoretical heat production and the theoretical heat production COP of M_optare significantly higher,the theoretical exhaust pressure is slightly higher and the theoretical exhaust temperature is significantly lower compared to the R22system.At the same time,the theoretical heating COP,the theoretical heating capacity,the theoretical exhaust pressure and the theoretical exhaust temperature of the M_optand R22systems all follow the same trend as the temperature drop of the heat source increases.