Study On Performance Of Medium-to-High Temperature Air-Source Heat Pump/Refrigeration System With Solar Injection Synergy

The combination of solar energy and air source heat pump/refrigeration systems can effectively reduce energy consumptions and environmental pollution caused by burning fossil fuels.Currently,most researches use water circulation systems to couple solar energy with steam compression heat pump/refrigeration cycle system,which wastes the power of solar energy.Solar ejector heat pump/refrigeration cycle system has great potential to realize heating/refrigeration by using solar energy as a driving force.The medium-to-high temperature air-source heat pump/refrigeration cycle system with solar injection synergy proposed in this subject uses a solar collector to provide a high-temperature and high-pressure primary fluid for the ejector,while a low-temperature and low-pressure refrigerant gas from the evaporator is injected into the ejector to increase the suction pressure of the compressor,thereby reducing the power consumption of the compressor in the system cycle and increasing the gas volume of the compressor,improving the performance of system.This will play an active role in promoting the development of energy-saving technologies for existed heat pump/refrigeration devices to bring better social and economic benefits.In this paper,a one-dimensional isobaric hybrid ejector model is adopted,in which,the compression sub-cycle uses R1234 yf and R134 a as the refrigerant,respectively,and the ejector sub-cycle uses R245 fa as the refrigerant.Through using FORTRAN programming,the combined analysis method of the energy model and the enthalpy model is applied to investigate the influence of the working conditions on the performance of the system.The research contents of this study consists of four sections:(1)A one-dimensional isobaric hybrid ejector model was established.The performance of the ejector was designed and calculated with the fluid media of R245fa.The experimental data were used to verify that the maximum error range of the ejector coefficient and the critical condensation temperature was within 15%.(2)The energy and enthalpy analysis model of the medium-to-high temperature air-source heat pump/refrigeration cycle system with solar injection synergy was constructed,and the simulation program related to the system performance was further compiled.(3)The performance of the cascade air source heat pump/refrigeration system was analyzed under the design conditions.The effects of condensation,evaporation,intermediate evaporation and generation temperature changes and different refrigerant combinations on system performance were studied.The main findings are concluded below:1)The performance of the R134a/R245 fa cascade air source heat pump/refrigeration system is better than the system with R1234yf/R245 fa refrigerant combination as the working fluid.2)With the increase of condensing temperature,the mechanical coefficient of performance COPm of the cascade heat pump system decreases,while the thermal coefficients of performance COPs and COPh? exergy destruction and exergy efficiency increase;The mechanical coefficient of performance COPm and exergy efficiency of the cascade refrigeration system reduce,while the thermal coefficients of performance COPs and COPh as well as exergy destruction increase.3)With the increase of evaporation temperature,the mechanical coefficient of performance COPm?thermal coefficients of performance COPs and COPh and exergy efficiency of the cascade heat pump system increase,while the exergy destruction decreases;The mechanical coefficient of performance COPm and total exergy destruction of the cascade refrigeration system increase,while the thermal coefficients of performance COPs and COPh and exergy efficiency decrease.4)With the increase of the intermediate evaporation temperature,the mechanical coefficient of performance COPm of the cascade heat pump system increases,while the thermal coefficients of performance COPs and COPh decrease.The exergy destruction presents decreasing at first and then increases,while the exergy efficiency has the contrast trend with an optimal operating point.The mechanical coefficient of performance COPm of the cascade refrigeration system and the total exergy destruction increase as the increasing of the intermediate evaporation temperature,while the thermal coefficients of performance COPs and COPh and the exergy efficiency decrease in constrast.5)With the increase of generation temperature,the mechanical coefficient of performance COPm?thermal coefficients of performance COPs and COPh and total exergy destruction of the cascade heat pump system increase,while the exergy efficiency decreases;The mechanical coefficient of performance COPm and total exergy destruction of the cascade refrigeration system are increasing,while the thermal coefficients of performance COPs and COPh and exergy efficiency reduce.6)In cascade heat pump system,the exergy destruction of each component accounts for the largest proportion of the total exergy destruction are ejector and solar collector,while ejector,condenser and solar collector account for the largest proportion of the total exergy destruction in cascade refrigeration system.(4)The performance of the cascade system is simulated of an energy-saving office building in Taiyuan City from July 1 to 7 in summer for cooling and January 1 to 7 in winter for heating respectively.The research results show that the hourly heating/cooling capacity,mechanical coefficient of performance,total exergy destruction and exergy efficiency of cascade heat pump/refrigeration system are consistent with the changing trend of the hourly solar radiation intensity.The performance of the system presents the best with the strongest solar radiation intensity,the largest daily average solar radiation intensity and the daily average heating and cooling capacity.The cascade heat pump/refrigeration system can meet the heating/cooling needs of the 250m2 office building during most of days.