Research On Control Strategy And Energy Consumption Simulation Of Subway Ventilation And Air Conditioning System Based On Modelica Modeling And Simulation

In recent years,as the main transportation method for urban residents,the energy consumption problem of subway has received more and more attention.Studies have shown that the annual non-traction electricity consumption of a single underground standard station is around 1.8 to 2.3 million kilowatt hours,with the energy consumption of the ventilation and air conditioning system accounting for the highest proportion,reaching 54% to 71%.Therefore,controlling the energy consumption of the subway ventilation and air conditioning system is expected to be an important measure to improve its energy-saving benefits.To improve the energy efficiency of the ventilation and air conditioning system and improve its operational performance,it is necessary to increase the research investment in the energy consumption simulation and control strategies of the subway’s ventilation and air conditioning system.However,traditional modeling and simulation platforms use imperative programming languages and causal modeling methods,with model equations and solving methods intertwined.In addition,in the existing subway ventilation and air conditioning system modeling and simulation,the modeling process of the thermal flow physical model and the control system model of the subway ventilation and air conditioning system is not clear enough.To address these limitations,this study used a Modelica language,which is an equation-based multi-domain modeling language based on object-oriented programming,to establish a subway ventilation and air conditioning system model library for the North Garden,Sports Park,and City Library stations of Line 2 of Xi’an Subway.The ventilation and air conditioning systems of these three subway stations were validated as examples,and the selection and control effects of new equipment for standard subway stations were evaluated,and corresponding optimization control strategies were proposed.(1)Based on Modelica modeling and simulation,the mathematical models of various object components(such as cooling towers,chiller units,and combination air handling units)of the subway ventilation and air conditioning system were studied,and a thermal flow physical system object model library was established.In addition,in order to better fit the characteristics of the subway’s underground public space,a spatial and load calculation model was constructed for subway public areas,which have significant differences in load characteristics from aboveground buildings and ordinary underground buildings.The human body heat dissipation and humidity requirements were calculated based on real-time pedestrian flow data as parameters,which further improved the simulation model library of the subway station’s building energy system and provided references for component modeling.(2)According to the actual control strategy of the subway ventilation and air conditioning system,corresponding work condition classification methods,system operation modes,and optimal control strategies and algorithms for each work condition were proposed.Based on this,a control system object model library was constructed,and its modeling process could provide references and guidance for the modeling of other ventilation and air conditioning control systems.(3)Based on the subway ventilation and air conditioning system thermal flow physical system and control system object model library,the ventilation and air conditioning systems of three standard subway stations were modeled,and a simulation model of the subway station’s air conditioning system was established with the same calculation of pipe network pressure distribution and seasonal ventilation and air conditioning control strategies as the actual engineering.The results showed that after optimizing the equipment selection,the control effect of the subway ventilation and air conditioning system met the design specifications.(4)To address the issue of the subway ventilation and air conditioning system’s inability to meet design specifications when the outdoor temperature is below 3 ℃ during the winter and ventilation seasons,the "ventilation-only" operating strategy was used as a solution.After optimization,the temperature control range of the ventilation and air conditioning system increased by more than 5.8%,and the overall energy consumption was reduced by about 60%.(5)Through simulation and load analysis of the subway station’s ventilation and air conditioning system during the air conditioning season,it was found that in extreme weather conditions,the ratio of infiltration and mechanical fresh air load at the entrance and exits of the standard station can reach up to 70% of the total load or as low as 40%,which is not conducive to energy-saving operation of the subway ventilation and air conditioning system.Based on this research result,a new control strategy and air conditioning system optimization were adopted,namely the indoor circulation mode.After optimization,the ratio of infiltration and mechanical fresh air load at the entrance and exits was reduced to 20% to 54%,and the energy-saving effect of the ventilation and air conditioning system was 31.4% to 45.4% compared to the original subway ventilation and air conditioning system.In summary,the subway ventilation and air conditioning system model library established based on Modelica can help design personnel quickly build models and conduct simulations during the subway ventilation and air conditioning system design phase,and construct a virtual experimental platform for subway ventilation and air conditioning systems that can flexibly change system structure and control strategies.The research results of this article provide a theoretical basis for predicting the performance and energy consumption of subway ventilation and air conditioning systems,optimizing system design and control strategies,and have important engineering application value.