Mechanical Ventilation Strategy for Subway Cabins Using Numerical Simulations

Abstract

Seoul metropolitan subway network is known to be the one of the most heavily used transportation means in the world. The subway cabins are naturally ventilated when the cabin doors are opened and through the gaps caused by the incomplete air-tightening of cabin bodies. Although, subway trains are equipped with a mechanical exhaust fan, the apparatus is rarely operated due to the problem of heating/cooling efficiency especially in the summer and winter seasons. In this study, we analyzed the transient CO2 (carbon dioxide) concentration level during the journey of a subway cabin when a heavy load of passengers of up to 200% of designed capacity using a CFD (computational fluid dynamics) analysis. With an increased journey time, the CO2 concentration increased by up to 5,000 ppm depending on passenger load. Through the operation of a mechanical exhaust fan, the high concentration of CO2 decreased down to 1,500 ppm. The effect of the exhaust fan operating on the dilution of indoor air was estimated by comparison with a closed cabin. In addition, the energy consumption for cooling in summer time was assessed for exhaust fan operations.