Research On The Operational Characteristics Of An High Efficiency Refrigeration Station Based On Optimized Control Of Air Conditioning Water System

The air conditioning energy consumption has the highest proportion in the total energy consumption of buildings,and the construction of high efficiency air conditioning refrigeration station is a critical approach to effectively mitigating the significant energy consumption associated with air conditioning operation and promoting sustainable development of green buildings.Therefore,implementing carbon reduction measures during the operational phase of air conditioning systems is a crucial link in achieving China’s carbon peak and carbon neutrality targets.In this study,the air conditioning plant of a photovoltaic enterprise in Yangzhou as the research subject.Field measurements were conducted to assess its operational performance under summer working conditions,and a simulation model of the air conditioning plant was developed using TRNSYS software for optimization research.Three variable frequency control methods for local optimization of the air conditioning water system were proposed in this research:firstly,constant temperature difference control for the chilled water system;secondly,constant pressure difference control for the chilled water system,and thirdly,a combination of constant temperature difference control for the cooling water system with variable frequency control for the cooling tower fans.In addition,an integrated optimization scheme was proposed,involving constant temperature difference control for the chilled water pumps and cooling water pumps,as well as variable frequency control for the cooling towers,with a setpoint of 6℃ for the temperature difference between the supply and return water of the pumps.Based on the established simulation model,the energy-saving effect of operating with a large temperature difference was investigated,and the results were used to retrofit the original air conditioning plant.The energy-saving effect of the retrofit was verified through statistical analysis of the monitoring system data after one year of operation.The primary research findings are summarized as follows:(1)Empirical research results under varying operational conditions reveal that altering the control strategy for pump operation in the air conditioning water system,specifically in terms of the quantity of pumps,can result in system instability.Furthermore,the original system exhibits a "large flow rate,small temperature difference" phenomenon,leading torelatively low system energy efficiency of approximately 3.5,necessitating the implementation of energy-saving retrofit measures.In addition,the utilization of TRNSYS software to develop a simulation model for the air conditioning water system yields simulation results that closely align with measured data,providing a robust foundation for subsequent energy-saving optimization analysis of the system.(2)A simulation study was conducted on three different variable frequency control methods for localized optimization.The results showed that all three control methods significantly improved the phenomenon of "large flow rate and small temperature difference" in the original system,and the total energy consumption was reduced by 27.3%,23.3%,and 28.1%,respectively.Furthermore,a comparison of the data revealed that there is still room for improvement in the system’s energy saving rate and COP,providing a reference basis for further research on group control optimization schemes.(3)A simulation-based study was conducted on an integrated optimization scheme,revealing that reducing the flow rate of chilled water and cooling water by 30%and increasing the supply-return water temperature difference by 40%,the system’s energy efficiency was improved,and the energy consumption of major equipment was reduced.The energy efficiency ratio(EER)of the system reached 6.1,which complies with the standards for high efficiency air conditioning refrigeration station.Furthermore,a simulation study on increasing the supply-return water temperature difference of chilled water and cooling water indicated that the larger the supply-return water temperature difference,the smaller the flow rate.The energy consumption of the system is reduced by more than 40%and as the temperature difference increases,the energy saving of the system increases,but the energy saving trend gradually decreases.(4)Based on the group control optimization strategies proposed in this study,the original system was retrofitted.Statistical results from one year of operation showed that the issue of high flow rate and low temperature difference in the original system is significantly improved.,with the EER of the optimized system reaching 5.0,meeting the standards for high efficiency air conditioning refrigeration station.This further validates the accuracy and practicality of the optimization simulations proposed in this study.The research conducted in this study aims to deepen the understanding of the operational characteristics of HVAC water systems,provide design and operation guidance for the construction of high efficiency air conditioning refrigeration station,and contribute to China’s efforts in energy conservation and emission reduction.