The Effect Of Piston Wind On Subway Environment And Energy Saving Character

For a subway station without the screen doors, the piston effect caused by the high moving train can markedly exchange the air in the tunnels, the platforms and the halls with the outdoor air, this is the prime power of the tunnel ventilation and the important air exchange way in the subway station. To effectively using the piston effect to reduce the energy consumption of the ventilation and air conditioning system, the influencing factors on the piston effect limited to the station and tunnel structure can be studied, when the train entering into the station, the positive pressure in front of the train should push the wasted air in the tunnel out through the shafts set in the tunnel mostly instead of the subway exits, when the train leaving the station, the negative pressure in back of the train should suck the outside air into the underground space through the way of exits- corridor- hall- platform as much as possible, and incidentally satisfy the fresh air needs of the passengers along the same route and ventilation. This methods will provide parts of the free fresh air without setting the fresh air shafts, save the underground space and the ventilation energy consumption. If taking the advantages of the large day-night temperature differences and the great thermal inertia of the underground soil in north China, the natural cold resource will be obtained, the air conditioning equipment capacity will be reduced, and the carbon emission and the energy in the initial construction and the operations management of the subway will be significantly decreased.Based on the design idea of using the piston effect to improve the air quality and reduce the energy consumption in the subway station. A subway station without the enclosed platform in Beijing China was chosen to conduct this study. The goal was to determine and evaluate the influence of the different piston air shaft setting modes on the airflow and the mass transfer in the subway station using the Dynamic Mesh model and the Species Transport model in the CFD software Fluent14.0. Additionally, four indexes(Air exhaust rate of piston air shafts, and Air intake rate of exits, air dilution rate and equivalent fresh air exchanges) were used to evaluate the impact of the piston effect on the subway air quality. The study shows: 1) The CFD methodology can simulate the airflow and the mass transfer in the subway. 2) For the subway station with the single shaft mode, in which the shaft is located at the entering portal of the tunnel. The intake of outdoor air due to the piston effect through the subway exits was 5126 m3. This was using the trains departing time interval of 250 seconds. This accounted for 52% of the whole intake of outside air. This was about 2 times more of the air intake for the same subway station using the double shaft mode. 3) The single shaft mode could not only save the land, but also intake more outside air through the subway exits, and the equivalent fresh air exchanges in the station corridor, halls and platform were 29.4 h-1, 32.0h-1 and 7.3 h-1respectively. The CO2 concentration in the three zones was also decreased. These results can provide the design reference for the piston air shaft for subway ventilation based on the piston effect.