Research On Dynamic Performance Of Solar Ejector Refrigeration System And Optimized With Multiple Ejectors

In the current energy context,decarbonization of the building industry is crucial.Achieving decarbonization in the building industry requires reducing energy consumption and CO2 emissions during the operation of buildings,which mainly stem from heating,ventilation,and air conditioning(HVAC)systems.The goal of reducing greenhouse gas emissions by 80% is difficult to achieve through traditional means,and the most promising approach is to use renewable energy.Ejector refrigeration systems can utilize low-grade thermal energy such as solar energy,but their performance is greatly affected by actual operating conditions and unable to operates efficiently.Therefore,it is necessary to conduct in-depth research on the dynamic performance of solar ejector refrigeration systems and adopt some methods to improve the performance of the system.A one-dimensional full-condition calculation model for ejectors was established.Actual gas physical properties were used in the modeling process and differences in the calculations of sound velocity between dry and wet fluids were considered.Moreover,a new expression for the subcritical momentum mixing coefficient was proposed according to the momentum mixing coefficient in critical condition and the outlet back pressure of ejector.Based on the ejector calculation model,Ejector refrigeration system calculation model was established,and the variable operating characteristics of six working fluid systems were compared.R1234 ze was eventually selected as the refrigerant for the solar ejector refrigeration system.Models of the solar ejector refrigeration system using R1234 ze as the refrigerant were established.The dynamic performance of the solar ejector refrigeration system during operation were investigated based on the established model.It was found that changes in operating parameters have a significant impact on the entire system.Keeping the inlet parameters of cooling water and chilled water unchanged,when solar radiation intensity deviates from the design value,the evaporation temperature increases,and both the system’s COP and cooling capacity decrease.The generation temperature and condensation temperature increase with increasing solar radiation and decrease with decreasing solar radiation.When the meteorological parameters and cooling water parameters do not change,the system’s COP and cooling capacity both increase with increasing chilled water inlet temperature.The evaporation temperature and condensation temperature also increase with increasing chilled water inlet temperature,while the generation temperature decreases.When the mass flow rate of chilled water increases,the generation temperature decreases,while the evaporation temperature and condensation temperature both increase,and the system’s COP and cooling capacity both increase.When the meteorological parameters and chilled water parameters do not change,the system’s COP and cooling capacity both decrease with increasing cooling water inlet temperature,while the generation temperature,evaporation temperature,and condensation temperature all continuously increase.When the mass flow rate of cooling water increases,the system’s COP and cooling capacity both increase,while the generation temperature,evaporation temperature,and condensation temperature all decrease.When the solar radiation intensity is higher than the design value,reducing the throttle valve opening can effectively increase the system’s cooling capacity.When solar radiation intensity decreases,increasing the throttle valve opening when the chilled water inlet temperature is lower and the cooling water inlet temperature is higher can slightly increase the system’s cooling capacity.To improve the overall performance of the system during operation,multiple ejectors are used to replace a single ejector to optimize the traditional system.A solar ejector refrigeration system with three ejectors was established,and the control strategy for the multi-ejector system was derived based on the change in cooling capacity of each ejector system with solar radiation intensity.The cooling load demand of summer users and the cooling performance of the ejector refrigeration system were compared and analyzed.The results show that during summer operating conditions,the average cooling capacity of the multi-nozzle solar ejector refrigeration system is 20.93% higher than that of the single-nozzle system,and the matching degree with user cooling demand is about 20% higher than that of the single-nozzle system,effectively reducing air conditioning energy consumption.