Throttling Characteristics And Injection Strategies For High Efficiency And Environmental Protection High Temperature Heat Pump Systems

In order to reduce greenhouse gas emissions,refrigerants with high global warming potential（GWP）are gradually being replaced by low-GWP environmentally friendly refrigerants.In High Temperature Heat Pump（HTHP）systems,appropriate electronic expansion valve（EEV）body structure and intermediate injection pressure control are crucial for their efficient,safe and stable operation.Aimed to fulfil the"dual carbon"goal of energy conservation and emission reduction in industrial process required for heat at temperatures of 100℃and above,this paper adopts a combination of simulation and experimental method to study the matching characteristics of the EEV opening and flowrate and further the refrigerant injection characteristics for HTHP systems in waste heat recovery field.HP-1 is chosen for the system,which is one China owned patent new environmentally friendly refrigerant.Moreover,comprehensive thermodynamic performance of HP-1 was compared with that of R245fa.This paper provides a good reference for the selection and control strategy of EEV for HTHP,and has theoretical and practical significance for improving the thermodynamic performance and safe,efficient operation of HTHP systems.The main research contents and achievements are as follows:（1）A mathematical model was established to describe the thermodynamic cycle process of the HTHP system with injection in MATLAB,and its accuracy was verified by experimental data.（2）Valve body structures that matched well with the new environmentally friendly refrigerant HP-1 were selected,and further the flow coefficient of EEV was obtained by fitting experimental data.Compared with the conical valve body,the elliptical conical valve body structure of the EEV can keep the openness between 1/3 and 2/3,maching well to the throttle characteristics for HP-1 HTHP system under variable working conditions.（3）The influence of injection pressure on system cycle performance was studied.Based on the system COP and safety performance,a reasonable control strategy for injection pressure was obtained.Various injection pressure control strategies were studied in terms of the system operation performance.The results showed that there are three typical injection pressures,corresponding to the maximum system COP,the lowest refrigerant temperature at the inlet of the EEV,and the lowest compressor discharge temperature.Based on the discharge temperature control strategy,the energy efficiency control strategy can effectively improve the system COP by 3.1%to 8.0%,while the discharge temperature will also increase by 6%to 8%.（4）From the perspective of comprehensive thermodynamic performance,the application potential of HP-1 as a substitute refrigerant was analyzed.The research illustrated that the thermodynamic and environmental performance of HP-1 was superior to that of R245fa.When the heat source temperature was 50℃and the heating temperature is 120℃,the heating effect of HP-1 could increase by 10.8%,the system COP increased by 2.7%,and the unit volume heating capacity increased by 10.3%.Moreover,HP-1 has a significant emission reduction effect,which can reduce CO₂emissions by 15.4%to 39.1%.