Study On Characteristics And Effective Utilization Of Fresh Air Infiltrating Into Entrances And Exits Of Underground Stations With Screen Doors

With the rapid development of urban rail transit,the energy consumption of rail transit represented by subway has gradually emerged,becoming the focus of attention among people.As an underground public building,the piston effect caused by the train makes the environment control system of the subway station unique.Current research on piston wind focuses on tunnel piston wind and wind leaking through platform screen doors（PSD）.There is not enough knowledge about the unorganized ventilation of h the entrance and exit passages（EEP）.It is difficult to achieve energy saving through the effective use of these unorganized fresh air.Therefore,it is necessary to study the characteristics and influencing factors of the unorganized fresh air at the EEP.At the same time,through the calculation of unorganized fresh air volume at this entrance,it can provide a reference for the design of the fresh air system,the operation of ventilation mode and temperature control,so as to achieve energy saving and emission reduction in the subway station.First of all,this paper conducts field research on 25 underground stations in Chongqing,and analyzes the status of underground stations from three aspects,including building structure,operation of stations and VAC system.And select 5 typical underground stations from the surveyed stations to test the unorganized fresh air at the EEP and the indoor environment.The test results show that the environment of the station is not only affected by the outdoor environment and the number of passengers,but also by the unorganized fresh air at the entrance and exit.Meanwhile,the data of unorganized fresh air shows that the fresh air is affected by the building structure,operation of trains,and the ventilation mode of VAC system,so that the influencing factors of unorganized fresh air volume can be determined initially.Then,on the basis of the measured data,analysis and discussion are conducted around each influencing factor.The results show that the depth of the station is the most important factor affecting the unorganized fresh wind at the EEP.The length of the entrance and exit channels are closely connected,and its influence on the air volume is also similar to the depth.The second is the ventilation mode of VAC system in the station.However,due to the the number of passengers and the period of station operation,the operation characteristics of trains have little effect on the unorganized fresh air in a certain period of time.Next,by analyzing the influence of the unorganized fresh air volume on the indoor environment of the station,it is found that the volume of unorganized air is a secondary influencing factor,which would not cause the significant fluctuations of the hot and humid environment and CO₂concentration in public areas.All this lays the foundation for the rational use of outdoor unorganized fresh air.Finally,combined with the measured data,this paper puts forward the effective unorganized fresh air volume indicators of different types of stations in different operating periods and different seasons.And the cooling load of the unorganized fresh air is calculated according to the enthalpy value of indoor and outdoor hourly,the index of unorganized fresh air cooling designed in the previous stage is also proposed.In addition,for different types of stations,energy-saving methods for the air-conditioning season and the ventilation season are proposed respectively.Compared with the traditional ventilation operation mode,the optimized annual energy saving of the VAC system is calculated.