Study On The Performance Of The Vapor Injected PVT Heat Pump System For Heating,Power Generation And Cooling

Building energy supply system based on solar energy is of great significance for building energy conservation,emission reduction and green building development in China.Conventional solar energy utilization has the bottleneck problems of poor heating stability and low solar energy efficiency,which greatly limited its wide application in buildings.In contrast,the photovoltaic-thermal(PVT)heat pump system has both heating and power generation function,has better stability and higher solar utilization efficiency,so it has great application potential.Although the PVT heat pump system can meet building's heating and electricity demand at the same time,while it cannot meet building's cooling demand,so it is hard to be widely used in building.Under this background,PVT heat pump system which has three functions of heating,power generation and cooling came into being and showed obvious technical advantages.However,when the system operates under the unfavorable environmental conditions of low temperature and weak solar radiation,the throttling loss is serious,the refrigerant circulation flow is small,and the heating performance is insufficient.Moreover,the cooling performance of the system under the ice storage condition also needs to be improved.Therefore,the vapor injected PVT heat pump system has been proposed in this paper,and comprehensive tests and theoretical studies on the system's heating,power generation and cooling performance have been carried out.First of all,in order to quantitatively investigate the performance of the vapor injected PVT heat pump system under actual conditions,an experimental system has been designed and established,and the heating,power generation and cooling performance of the experimental system has been studied,respectively.Results showed that the average power generation efficiency and COP of the system were 13.20%and 3.10 in winter,13.06%and 5.20 in summer,respectively,during the water heating tests.During the space heating tests in winter,the average COP of the system was 2.65.During the cooling tests in summer night,the average EER of the system is 2.12.Secondly,in order to determine the optimal heat exchange area of the economizer,and to clarify the rules of the environmental parameters' influence on the system's heating,power generation and cooling performance,a simulation model of the system was established in this paper.Then the accuracy of the simulation results has been verified.The performance of the vapor injected PVT heat pump system has been optimized and analyzed by using the simulation model.Results showed that the heating and cooling performance of the system can be effectively improved by increasing the economizer's heat exchange area,and the optimal ratio of the economizer's heat exchange area and the compressor's displacement volume is 5.63×10^-2h/m.What's more,both of the rise of ambient air temperature and the enhancement of solar irradiation have great promotion effects on the system's heating performance.The COP of the system is approximately linearly correlated with the above two ambient parameters.When the system working at the cooling condition,the rise of ambient air temperature and effective sky temperature have negative effects on the system's cooling performance.On the contrary,the increase of wind velocity can improve the system's cooling performance.However,when the wind velocity is further increased above 2m/s,its improvement effect on the refrigeration performance of the system is no longer obvious.In addition,night sky radiation is the main heat dissipation way of the PVT modules,and the higher the ambient air temperature is,the lower the wind velocity is,the proportion of sky radiant heat in the total heat dissipation of the PVT modules is,which can reach more than 70%.Thirdly,in order to quantitatively analyze the performance advantages of the vapor injected PVT heat pump system,the heating and cooling performance of this system and the conventional PVT heat pump system has been compared.Results showed that the vapor injected PVT heat pump system has obvious advantages over conventional PVT heat pump system in the same configuration and the same environmental conditions.The increase of heating capacity and COP could be more than 30%and 15%respectively.And the more severe the environmental condition is,the more obvious the heating performance advantage of the vapor injected PVT heat pump system is.In addition,the cooling performance of the vapor injected PVT heat pump is better,too.The increase of cooling capacity and EER could be more than 25%and 12%,respectively.Moreover,the lower the ambient temperature is,and the higher wind velocity is,the more obvious the cooling performance advantage of the vapor injected PVT heat pump system is.Fourthly,in order to meet the design requirements of the vapor injected PVT heat pump system,this paper puts forward the 10 coefficient calculation model.By using this calculation model,the heating performance of the vapor injected PVT heat pump system during heating period and the cooling performance of the system during cooling period of Dalia have been calculated and analyzed in this paper.Results showed that the vapor injected PVT heat pump could operate reliably more than 93%of the whole heating period of Dalian,and the average COP of the system was 2.40.The average EER of the system was 2.68 during the summer night of the cooling period of Dalian.Finally,space heating and cooling guarantee rates have been put forward in this paper for evaluating the matching relationship between the vapor injected PVT heat pump system's heating/cooling ability and the building's heating/cooling demands.When the vapor injected system is applied to residential buildings in China,its heating and cooling guarantee rates have been predicted.On this basis,the matching relationship between the capacity of the vapor injected PVT heat pump system and the building's heating/cooling area has been analyzed.Results showed that the building's space heating/cooling area that can be well matched with the unit system capacity is 17m² for Shenyang(extreme cold region),31m² for Beijing(cold region)and 25m² for Wuhan(hot summer and cold winter region),respectively.Then the regional adaptability of the system has been analyzed based on the matching results of the system's capacity and the heating/cooling area of the residential building in 25 provinces of China(except for the hot summer and warm winter region and mild region).Results showed that the vapor injected PVT heat pump system is suitable for the central part of China,and has great application potential in building heating in Tibet of China.