Effects of Train-Induced Unsteady Airflow on Air Quality and Air Distribution in a Subway Station

Using train-induced unsteady airflow in transitional seasons can greatly reduce the energy consumption of a subway station's mechanical ventilation. However, the unsteady airflow carries the particles from tunnels into subway platforms, and airflow distribution at controllable vents is uneven. To determine the variation in PM2.5 (particulate matter of 2.5 micrograms or less) concentration and the air velocity distribution at the vents, field tests were conducted. The results showed that the PM2.5 concentrations at the vents and platform were positively correlated with the air velocity. The average ratio of the PM2.5 concentration at the vents to that on the platform was 71.15%. The maximum PM2.5 concentration and average PM2.5 concentration on the platform were 0.067 mg/m(3) and 0.037 mg/m(3), respectively. The air velocity distribution along the length of the platform conformed to logistic regression. Adjustment of the opening height of the vents was proposed to improve the air velocity distribution. Through numerical simulation, the ratio of the minimum airflow rate to the maximum airflow rate was increased from 5.9% to 37.5% after adjustment. This method is helpful for the uniform distribution of the airflow rate. This study will provide references for the design and operation of the vents of subway stations.