Environmental health in subway stations, a typical type of urban underground space, is becoming increasingly important. Ventilation is the principal measure for optimizing the complex physical environment in a subway station. This paper narratively reviews the environmental and health effects of subway ventilation and discusses the relevant engineering, environmental, and medical aspects in combination. Ventilation exerts a notable dual effect on environmental health in a subway station. On the one hand, ventilation controls temperature, humidity, and indoor air quality to ensure human comfort and health. On the other hand, ventilation also carries the potential risks of spreading air pollutants or fire smoke through the complex wind environment as well as produces continuous noise. Assessment and management of health risks associated with subway ventilation is essential to attain a healthy subway environment. This, however, requires exposure, threshold data, and thereby necessitates more research into long-term effects, and toxicity as well as epidemiological studies. Additionally, more research is needed to further examine the design and maintenance of ventilation systems. An understanding of the pathogenic mechanisms and aerodynamic characteristics of various pollutants can help formulate ventilation strategies to reduce pollutant concentrations. Moreover, current comprehensive underground space development affords a possibility for creating flexible spaces that optimize ventilation efficiency, acoustic comfort, and space perception.

In subway stations, the piston effect plays an important role in enhancing ventilation to improve subway environment and reduce energy consumption. However, it may induce negative impacts on environmental health and thermal comfort, i.e. air pollution and strong wind. Traditionally, the architecture and ventilation systems are designed separately, and normal ventilation design follows architectural layout. Actually, the architecture design can have a significant influence on the ventilation performance, e.g. airflow pattern. Therefore, this study aims to integrate the design pattern of the architecture with an appropriate ventilation system. A typical subway station of Nanjing (in China) was considered. A dynamic-mesh based computational fluid dynamics (CFD) method was adopted to simulate ventilation performance in the presence of piston effect. Field measurements were conducted to validate the numerical method. New measures were proposed from the perspectives of architectural design to improve the ventilation effect, including enlarging atrium space, adding atrium vents and funnel-shaped exits, etc. The numerical results show that the optimal architectural design could provide a significant improvement towards the airflow environment and ventilation efficiency while avoiding serious air pollution. The proposed integrated-design pattern could further facilitate the creation of an ‘energy-saving’ and ‘healthy’ underground space environment.

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The sunken courtyard has long been used in underground spaces and provides an important outdoor environment. It introduces natural elements to create a pleasant space for human activities. However, this study measured a typical sunken courtyard and found potential problems of excessive solar radiation and accumulated air pollutants in summer when at an acceptable outdoor temperature for human activities. To improve the comfort and health of a sunken courtyard, this research proposes some green retrofit designs. Firstly, compared with green wall, water and a tree, sunshade is a primary measure to improve thermal comfort. Combining sunshade, a green wall and water reduces the temperature by up to 5.6 °C in the activity zone during the hottest hour. Secondly, blocking/guiding wind walls can effectively improve the wind environment in a sunken courtyard, but only when the wind direction is close to the prevailing wind. A blocking wind wall was better at affecting velocity and uniformity, while the guiding wind wall was more efficient at discharging air pollutants. This study initially discusses the climate-adaptive design of underground spaces in terms of green, thermal comfort and natural ventilation. Designers should generally integrate above/underground and indoor/outdoor spaces using natural and artificial resources to improve comfort and health in underground spaces.

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