Measurement of Natural Ventilation Rate in Seoul Metropolitan Subway Cabin

Abstract

The increasing concerns regarding the management of indoor air quality have become an important issue for subway operators because most subway lines are underground and have poor ventilation. To maintain clean and fresh indoor air in cabins with low consumption of energy it is first necessary to quantify the components of the ventilation in the cabins divided into mechanical ventilation and natural ventilation. However, there is no established method of, nor reliable data on, how much indoor air is exchanged through natural ventilation such as doors opening and closing. In this study, carbon dioxide (CO2) levels were measured in 6 lines of the Seoul Metropolitan Subways and a theoretical approach was made to estimate the indoor CO2 levels through natural ventilation during the operation of cabins to calculate the natural ventilation rate. We considered CO2 dilution factor during natural ventilation which indicates the exchange rate of indoor air with outdoor air. As the result of the study, the change in CO2 level could be quantified and it was found that approx. 35% of the indoor air was exchanged with outdoor air through natural ventilation.