Study On The Performance Of The Dx-sahp Water Heater With Variable Capacity On The Full Conditions

Driven by technological advance and environmental needs,global energy consumption is decelerated and the energy structure is shifting towards cleaner and lower carbon direction.Through the integration of collector and evaporator,higher evaporating temperature and collector efficiency are achieved in the direct-expansion solar-assisted heat pump(DX-SAHP),which results in the higher coefficient of performance.Theoretical and experimental study on the operating performance and control mode were performed.The effects of operating parameters were analyzed and the control strategy was developed,which realized the optimizing operation of the system.A DX-SAHP system experimental platform was built,which was mainly consisted of a bare solar collector/evaporator,an inverter compressor,a microchannel condenser,an electronic expansion valve and data acquisition and control system designed.The system was charged with 1000 g R134a.The preliminary testing results showed the DX-SAHP system operated well.In the typical summer condition,the average coefficient of performance reached 5.43,and the average of collector efficiency reached 1.17.The simulation model for the experimental platform was built,which consisted of the property model of R 134a and models of system components.Based on the MATLAB software,the simulation program was written.The operating parameters of the system on multi conditions were simulated,which proved the error of the simulation model was less than 12%.The operating performance of the system was simulated and analyzed on the typical conditions.With solar radiation intensity of 650 W m-2,the average coefficient of performance was 5.40 and the average of collector efficiency was 1.25,whereas the average coefficient of performance was 4.00 and the average of collector efficiency was 3.06 with solar radiation intensity of 200 W·m-2,which proved the DX-SAHP system had good heating capacity even on of condition with low solar radiation.The simulation analysis of control parameters in operating was performed including of superheat degree and speed of compressor.The ideal range of superheat degree was concluded as 5-10℃ and the ideal operating mode of the compressor was concluded as variable mode regulating with solar radiation.The ideal angle of the solar collector/evaporator was concluded as 45°-60° for area with latitude of 36°.Combined with DX-SAHP simulation model and simplified model of solar radiation the study on heating time was performed and fitting function of heating time and initial water temperature was developed.Based on the superheat degree and compressor speed,the control strategy for the DX-SAHP with variable capacity was developed and tested on full conditions,which proved it could control the heating time accurately and achieve a higher coefficient of performance.