| Solar energy,as a clean energy which can be widely used,has been received more and more attention from countries and scientists.Direct-expansion solar-assisted heat pump(DX-SAHP)technology combines solar energy utilization technology and heat pump technology,which can overcome the problems of solar intermittent,cloudy and rainy days,and also improve the performance of the heat pump system.The DX-SAHP system integrates the heat collector and the evaporator,which obtains a higher concentration and heat collection efficiency,and improves the system coefficient of performance(COP)relative to the indirect system.The operation characteristics of R290 DX-SAHP water heater and the influence of various parameters are analyzed.The main research contents are as follows:Designed and constructed a micro-channel DX-SAHP water heater experimental system using R290 as the refrigerant.It is mainly composed of heat pump body(Micro-channel solar collector/evaporator,R290 compressor,micro-channel condenser,heat storage tank and electronic expansion valve,etc.)and data acquisition control system.In this paper,the working principle and system design,selection and assembly process of the heat pump experimental platform are introduce,mainly including the structural parameters and models of the four major components of the heat pump system,the working principle and composition of the data acquisition control system,pyranometer,pressure sensor,temperature sensor,anemometer,Single-phase wattmeter,mass flowmeter and other hardware devices and sensors.System control program and collection and input of experimental data to achieve control of the heat pump experimental platform(expansion valve opening,system start and stop),monitoring of environmental parameters and operating parameters,collection and storage.Through the experimental research under the overall working conditions and the analysis of a large number of experimental data,it proves that the R290 micro-channel DX-SAHP system has excellent performance.Annual experimental research results showed that the experimental system operates efficiently and safely under sufficient working conditions.Under all operating conditions,the maximum heating power of the system is 2140.5 W and the minimum is 739.6 W,the average heating power during the same period is 1358.6 W,the maximum COP of the system is 5.99,the minimum is 2.04,and the average average COP is 3.88.The system operation conditions are similar in spring and autumn conditions.The system COP is maintained above 3.5.Even under the harsh winter conditions,the average system COP can still be maintained 3.0.In summer condition,the system performance is excellent,and the COP value is maintained at around 5.0,up to 5.99.The comparison test with the DX-SAHP system using R134a as the working fluid shows that the performance of R290 refrigerant in the DX-SAHP system is basically the same as that of R134a refrigerant.Therefore,it can be verified that R290 refrigerant can be applied to a direct expansion solar heat pump system,and can provide good system performance.For the flammable refrigerant R290,charge volume research is crucial.Therefore,in this paper,the R290 micro-channel DX-SAHP system was tested for charging volume.The research results show that under certain conditions,the increase in refrigerant charge will increase the COP,heating power,and compressor power of the DX-SAHP system,which will be more significant under extreme conditions of low solar radiation.In this system,the safety,economy and efficiency of the system are comprehensively considered,and the refrigerant charge of the system is set at 0.35 kg.In addition,as the charging volume increases,the system’s evaporating pressure,evaporating temperature,condensing pressure,and condensing temperature all increase slightly. |
