Research On Optimal Control Of Air Conditioning Water System In Subway Stations

With the accelerated urbanization,subways have become the main means of transportation for commuters.The ventilation and air conditioning system of a subway station ensures the comfort of passengers,but also consumes a large amount of energy accordingly.This paper aims to reduce the energy consumption of the air conditioning water system by studying the optimization strategy of the air conditioning water system in a metro station in Guangzhou.This project combines the project profile of a metro station in Guangzhou and the climatic parameters of the place,and analyzes its load composition.A load model of the metro station was established using TRNSYS to calculate the hour-by-hour cooling load during the cooling season,and the error range was within 5% compared to the load design value,and this result verified the accuracy of the building model.At the same time,a more accurate equipment model was established by parameter fitting using sample data provided by the equipment manufacturer,and a basic model of the air conditioning water system of the metro station was built.It provides the basis for the subsequent optimization of the water system control strategy modeling.Simulation of the basic model of the water system to evaluate its energy consumption and provide a reference benchmark for the subsequent optimization of the control strategy energy saving rate.For the "large flow rate,small temperature difference" phenomenon,a fixed temperature difference control strategy is proposed to reduce the energy consumption of the water system.Simulation results show that compared with the water system without optimal control,the water system with fixed temperature difference control strategy can achieve an energy saving rate of25.86%,laying the foundation for further optimization research.For the cooling water control strategy,three different optimal control strategies were studied: variable cooling tower discharge temperature control strategy,cooling water variable temperature difference variable flow control strategy and both combined control strategies.Compared with the water system with fixed temperature difference control strategy,the energy saving rate of the water system with variable cooling tower discharge temperature control strategy and variable cooling water temperature difference variable flow control strategy and combined variable temperature difference variable flow control with variable cooling tower discharge temperature increased by 6.63%,5.74% and 7.98%,respectively.The control strategy of the chilled water system was studied to determine the optimal water supply temperature control strategy under the consideration of different load rates to meet the end cooling demand.For the fixed temperature difference control strategy with variable water supply temperature,the optimal water supply temperature of the chilled water system and the energy consumption of the water system under this control strategy were analyzed.The results show that the strategy can save about 3.40% energy compared to the water system with a fixed temperature difference of 7°C as the water supply temperature.In order to further reduce the energy consumption of the air conditioning water system,three control modules were used: "set cooling tower discharge temperature","set cooling water supply and return temperature difference" and "set chilled water supply temperature ",the water system with fixed temperature difference was optimized and controlled.Compared with the water system with fixed temperature difference,the energy saving rate of the optimized water system was increased by 10.84%.