Optimization Of Low GWP Refrigerant For Water Source Heat Pump Unit

Refrigerant R22 is about to be eliminated due to its destructive effect on the ozone layer.During the exploration of alternative refrigerants,the mixed refrigerant R410a gradually occupied the market with its excellent thermodynamic performance and friendliness to the ozone layer and began to be widely used until the global warming effect has intensified,and the greenhouse effect of refrigerants is becoming more and more concerned.Research and development of environmentally friendly refrigerants with low GWP is the current trend in the world's refrigeration industry,and it is also a top priority.As a large-scale refrigeration country,China should avoid blindly obeying environmental protection requirements and economic and technological constraints.Adopting mixed refrigerants as a transitional option may be the most secure choice at this stage.This project has selected a new type of refrigerant NC01,which is a mixture of R32,R134a and R1234ze refrigerants,with an ODP value of 0 and a GWP of 750.It is directly charged in the existing water source heat pump unit and simulated by experiments and simulations.Through experiments and simulations,the effects of refrigerant charge,expansion valve opening,water temperature,and water flow rate on the performance of the heat pump system were studied,so as to achieve the above factors without changing the hardware of the original unit.The purpose of efficient operation of the heat pump unit.In order to verify that the refrigerant NC01 can be directly charged in the original R410a unit,the basic physical properties and thermal cycle performance of the refrigerants NC01 and R410a are compared and analyzed by the software Refprop9.0.The molecular weights and saturated liquid densities of the two refrigerants are compared.Saturated gas pressure,latent heat of vaporization and other aspects are all very similar.Through thermodynamic cycle analysis,the corresponding compressor discharge pressure and exhaust temperature of NC01 are lower than R410a,and the power consumption and unit heating capacity are slightly higher than the latter.The refrigerant NC01 has good adaptability to the original heat pump unit.Original water source heat pump test rig was used to conduct experiments to study the effect of water temperature,water flow rate,and expansion valve opening on heat pump performance.The results show that:Under different hot water outlet temperatures,the cold water inlet temperature rises from 13 0C to 20?,and the unit COP increases by 20%to 30%.When the inlet temperature of cold water is lower than 17?,the heating amount and COP of the system are the highest when the opening degree of the expansion valve is 60?.The heating value and COP of the system corresponding to the opening degree of the expansion valve 70%when the cold water inlet temperature is higher than 17? is the highest.Increasing the evaporator side cold water flow within a certain range can improve the system performance.As the water flow continues to increase,the impact on the system performance becomes smaller and smaller.The heat pump system simulation model was established based on Simulink,and the error between the simulation results of the model and the experiment is within 10%.Then the model was used to analyze the effect of changes in the refrigerant charge on the system performance.The results showed that the heat pump unit performance is best when the refrigerant charge is 7kg.