| Air source heat pump water heaters meet approval with the international market because of its characteristics of obtaining energy from low grade energy to heat domestic hot water.In recent years,researchers have made some achievements in the energy-saving optimization of water heaters under the international situation of energy shortage.However,there is still room for improvement in reducing the energy cost of air source heat pump water heaters in the heat preservation mode and ensuring the energy supply in the energy consumption mode for users at the same time.Therefore,a new type of stratified thermal storage heat pump water heater system was proposed in this research.In order to obtain different heat preservation temperature,double compressors and condenser coils were set to operate in parallel to heat the upper and lower water tanks,which had been divided into two layers.The heat preservation temperature of lower water tank can be reduced and the system structure can be adjusted.Thus,stratified thermal storage heat pump water heater system can ensure the energy efficiency and reduce the energy cost of heat preservation.Firstly,the coupled model of energy consumption and one-dimensional heat transfer model of heat preservation are established respectively simulating the energy consumption and heat preservation performance of the stratified thermal storage heat pump water heater system.In the coupled model of energy consumption,the cycle of the air source heat pump was established by MATLAB to simulate the closed cycle process of the four components.CFD was used to build the model of the water tank,and the flow and heat transfer process of hot water in the tank were simulated.The coupled model of energy consumption is formed by coupling the two models to simulate the performance of the system during.In heat transfer model of heat preservation,the heat transfer model between the water tank and external environment was established by MATLAB.In Nanjing zone,a certain brand model of heat pump main engine was used,the experimental platform of heat pump water heater system was design and build.The annual hourly energy cost in the heat preservation mode of stratified and non-stratified thermal storage heat pump water heater system were calculated,and the heat preservation performance of the two systems were compared.The performance of the non-stratified thermal storage heat pump water heater system in the heat preservation mode and the energy consumption mode is tested and the temperature distribution in the water tank and the outlet temperature are measured.The simulation results were in good agreement with the experimental results,and the reliability of the model is proved.Secondly,in the mode of energy consumption and heat preservation of the stratified and non-stratified thermal storage heat pump water heater system are simulated by using the established the coupled model.For the process of energy consumption,this research compares the system performance of the stratified and non-stratified thermal storage heat pump water heater system and analyzes whether the stratified thermal storage heat pump water heater system can meet the needs of daily users.For heat preservation mode,energy cost全年逐时保温能耗of heat pump water heater for heat preservation was calculated,the heat preservation performance of the stratified and the non-stratified thermal storage heat pump water heater system were compared.The simulation results show that:after the stratified thermal storage technology is adopted in the heat pump water heater,the heat stratification in the water tank increases,the average outlet water temperature and the energy releasing remain the same when the system is in the energy consumption mode,whereas the efficiency of energy release increases by 14.96%.When the system is in the heat preservation mode,the stratified thermal storage heat pump water heater system is used in Beijing,Guangzhou,Nanjing,Shanghai and Chongqing,and the annual energy consumption of heat preservation is reduced by 20.42%,23.73%,21.30%,21.62%and 22.27%compared with the non-stratified thermal storage heat pump water heater system,which indicates the stratified thermal storage heat pump water heater system can meet the actual needs of users and achieve the effect of energy saving.Finally,by simplifying the use situation of domestic hot water,it is assumed that the time of domestic hot water use and energy storage is concentrated at 19:00-21:00 every day.and the energy cost of all-day operation is the sum of the energy cost of heat preservation,energy consumption and energy storage of the day.Based on this,in the annual operation mode,the hourly energy cost of the system is calculated throughout the year,and the operating performance of the stratified thermal storage heat pump water heater system is compared with that of non-the stratified thermal storage heat pump water heater system.The simulation results show that: When the system is in the annual operation mode,the stratified thermal storage technology is adopted in Beijing,Guangzhou,Nanjing,Shanghai and Chongqing zone,respectively.The annual energy cost is reduced by 13.39%,13.57%,13.44%,13.46% and 13.52%compared with the non-stratified thermal storage heat pump water heater system.The research results show that: the stratified thermal storage heat pump water heater system has higher energy saving characteristics. |
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