Study On Operating Performance Of Heat Pump Water Heater And Heat Transfer For R417A In Spiral Tube-in-tube Condenser

With the development of economy and the enhancement of living standard,the demand for hot water by inhabitants living in both city and countryside increases,which contributes to a consuming market of hot water,with a large quantity and extensive scale.Air-source heat pump water heater is becoming popular in the global maket because of its high efficiency and flexibility in the view of energy utilization.This paper concentrated on system performance optimizing and researching on the refrigerant flux characters of air-source heat pump water heater for residential requirement.The performance of heat pump water heater also depends on the property of refrigerant in a certain extent.Ozone depletion potential of R417A is zero and has the characteristics of energy saving,environmental protection,high efficiency and easy replacement,so it has become a good substitute for R22.Condenser is one of the key components,and its heat transfer effect directly affects the performance of the whole heat pump system.A air-source heat pump water heater,using R417A as the working medium,was designed and set up,and a spiral tube-in-tube heat exchanger was used for condenser.The experiment was conducted at the range of water flow from 0.6 to 1.0m3/h,the range of water temperature from 17℃ to 55℃.In different conditions,the environment temperature is 15℃ and 29 ℃,the change of heat absorption and system performance(COP)and compressor power input of air source heat pump water heater were studied,and condensation heat transfer characteristics of the refrigerant R417A in spiral tube-in-tube condenser,the system performance of heat pump water heater were studied using R417A、R134a、R22 respectively.(1)At a certain inlet water temperature,the total heat transfer rate and total heat transfer coefficient increase with the increasing water flow rate and the heat transfer capacity increase with the increasing environmental temperature.Inlet water temperature is 20 ℃,environment temperature is 29 ℃,when water flow rate increases from 0.6m3/h to 1.0 m3/h,the total heat transfer rate and total heat transfer coefficient increase by about 18.8%and 20.6%respectively and increase by about 5.2%～9.7%.6.4%～11.7%in environment temperature is 29 ℃ than that in 15 ℃ respectively.At direct flow,inlet water temperature is 17 ℃,environment temperature is 29 ℃,when water flow rate increases from 0.6m3/h to 1.0 m3/h,the total heat transfer rate and total heat transfer coefficient increase by about 23.6%and 27.8%respectively and increase by about 7.2%and 10.5%in environment temperature is 29 ℃ than that in 15 ℃ respectively.(2)At a certain inlet water temperature,the suction and discharge pressure and input power of compressor increase and the heating capacity and heating coefficient of heat pump system increase with the increasing water flow rate.Inlet water temperature is 25 ℃,environment temperature is 29 ℃,when water flow rate increases from 0.6m3/h to 1.0m3/h,the suction、discharge pressure and input power of compressor decrease by about 5.1%、16.7%and 5.3%respectively and increase by about 51.4%～60.8%、11.3%～13.7%、17.3%～20.7%in environment temperature is 29 ℃ than that in 15 ℃ respectively.The heating capacity and heating coefficient of heat pump system increase by about 13.2%and 15.2%respectively and increase by about 23%～39%、14.6%～23.5%respectively in environment temperature is 29℃than that in 15 ℃ respectively.At direct flow,inlet water temperature is 17℃,when water flow rate increases from 0.6m3/h to 1.0m3/h,the suction、discharge pressure and input power of compressor increase by about 21.3%、28.4%and 14.8%in environment temperature is 29℃.(3)At a certain water flow rate,the discharge pressure and input power of compressor increase and the heating capacity and heating coefficient of heat pump system decrease with the rising inlet water temperature.Water flow rate is 0.6m3/h and environment temperature is 29℃,when inlet water temperature rises from 25℃ to 55 ℃,the discharge pressure and input power of compressor increase by about 55%and 46.4%respectively and increase by about 14.4%～18.7%、12.4%～19.7%in environment temperature is 29 ℃ higher than that in 15 ℃.The heating capacity and heating coefficient of heat pump system decrease by about 54%and 58.3%respectively and increase by about 18.4%～31.7%、23.6%～39.5%respectively in environment temperature is 29℃than that in 15℃.(4)Condensation heat transfer coefficient of R417A in annular channel decreases with the increase of saturation temperature,and local condensation heat transfer coefficient increases with the increasing dryness.The condensation heat transfer coefficient of R417A decreases from 3839W/(m2·K)to 2372W/(m2·K),about 38.1%when water flow rate is 0.6m3/h and saturation temperature rises from 40 ℃ to 60 ℃.Water flow rate is 0.6m3/h and refrigerant dryness decreases from 0.7 to 0.1,the local condensation heat transfer coefficient decreases by 17.5%、24.1%、29.4%when the condensation saturation temperature is 40℃,50℃ and 60℃respectively.(5)A air-source heat pump water heater,using respectively R417A、R134a and R22 as the working medium,was designed,and a spiral tube-in-tube heat exchanger was used for condenser,when environment temperature is 15 ℃ and water flow rate is 1.0m3/h.The compressor suction exhaust pressure and power input change consistent and R22>R417A>R134a with the increase of condenser water inlet temperature.when inlet water temperature rises from 25℃ to 55 ℃,the discharge and exhaust pressure of compressor decrease by about 3.68%～4.89%、14.76%～19.85%in R417A system lower than that using R22 and increase by about 27.6%～30.9%、12.76%～17.85%than that using R134a;input power of compressor decrease by about 11.76%～15.85%in R417A system lower than that using R22 and increase by about 20.76%～26.85%than that using R134a.(6)The heating capacity and heating coefficient of heat pump system decrease with the increasing water flow rate and R22>R417A>R134a、R134a>R22>R417Arespectively when environment temperature is 15 ℃ and water flow rate is 1.0m3/h.when inlet water temperature rises from 25 ℃ to 55 ℃,the average heating capacity of heat pump system using R417A is equivalent to 88%of using R22,and using R134a is equivalent to 74%of using R417A;the heating coefficient using R417A lower than that using R22 about 2.45%～3.76%,using R417A lower than that using R134a about 4.6%～7.9%.The study result has important theoretical significance and engineering application value for optimization design of condenser and energy saving operation of heat pump system in the refrigerant replacement.