| Solar absorption refrigeration system is of great significance for reducing primary energy consumption and reducing carbon emissions.However,single-effect or double-effect solar absorption refrigeration systems have problems such as low temperature range for heat source utilization,insufficient solar energy utilization,high initial investment,which affect the popularization and application of the system.In order to improve the adaptability of solar refrigeration system to heat sources with different temperatures,increase the solar fraction and reduce the system cost,this work proposed and optimized the single/double-effect switching solar Li Br-H2O absorption refrigeration system.The corresponding mathematical model of the system was developed,and the numerical simulation and optimization of operating parameters were completed.The main research work carried out in this project and the main conclusions obtained include:（1）In order to improve the adaptability of solar refrigeration system to different heat sources at different temperatures,a single/double-effect switching solar Li Br-H2O absorption refrigeration system composed of two independent chillers and solar heat collection system was proposed.The simulation model of the system was developed.The numerical simulation of the system was completed with the help of TRNSYS software platform,and the operation characteristics of the system without auxiliary heat sources were obtained.Under the weather conditions with high solar radiation intensity,the system could switch between single-effect and double-effect operation modes.The maximum daily cumulative cooling capacity of the system could reach 75.5 k Wh,and the maximum daily cooling time was about 10.5h.（2）In order to study the influence of different heating modes of auxiliary heat sources on the operation characteristics and performance of single/double-effect switching solar Li Br-H2O absorption refrigeration system,combined with practical engineering background,the single/double-effect switching solar Li Br-H2O absorption refrigeration system with different auxiliary heat sources heating modes was compared and analyzed.The single/double-effect switching solar Li Br-H2O absorption refrigeration system with double-effect loop auxiliary heating could realize the switching operation between single-effect,double-effect and double-effect driven by auxiliary heat source for one week.The cumulative cooling capacity could be 480.57 k Wh,with an average COP of about 0.95.The solar fraction of the system operating continuously for one week could reach 79.03%,which was 19.11%and 35.78%higher than that of the single/double-effect switching solar Li Br-H2O absorption refrigeration system with single-effect loop auxiliary heating and solar double-effect Li Br-H2O absorption refrigeration system with auxiliary heater respectively.（3）In order to evaluate the rationality and practicability of the system design,the economic analysis of the single/double-effect switching solar absorption refrigeration system was carried out by using the leveling cost.The analysis results show that the cost of collectors and refrigerators were relatively high,accounting for 41.63%and 48.04%respectively.Therefore,to improve the practicability and extensibility of solar refrigeration system,it can be achieved by reducing the cost of collectors and absorption chillers.（4）In order to select the appropriate optimization variables and reduce computational complexity in the optimization process,Sobol global sensitivity analysis method was used to analyze the influence of parameters such as collector area and hot water flow rate on solar fraction.According to the results of sensitivity analysis,it was the most effective system optimization measure to select the heat collection area,storage tank volume and operating parameters in double-effect mode as optimization variables.（5）In order to improve the solar fraction of the system and reduce the cost,NSGA-II multi-objective genetic algorithm was adopted to optimize the single/double-effect switching solar Li Br-H2O absorption refrigeration system with the objectives of maximizing the solar fraction and minimizing the leveling cost.The solar fraction of the optimized system was 89.73%,which was increased by 10.70%,and the leveling cost was4171.80 CNY,which was decreased by 4.57%.The reduction of collector area was the main reason for the reduction of system cost.After optimization,the carbon dioxide emission of the system was reduced by 58.29%,and the daily cumulative cooling capacity per unit collector area was increased by 19.05%.Through optimization,the system performance has been significantly improved. |
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