Cooling of Underground Railways

摘要

Underground railway systems can generate enough heat from their operations to raise tunnel and station temperatures substantially. This may result in passenger discomfort in warm weather conditions if the underground railway environment is not cooled. Ventilating an underground railway environment in which there is heavy traffic of electrically propelled rapid transit trains differ from those normally encountered in conventional air conditioning. The heat generated by the train motors and electric lighting, together with body heat from passengers, is so great that excessive temperatures would prevail in summer unless a high volume of air is supplied. This in some older underground railway systems is difficult to achieve. The installation of in car air-conditioning units adds another major heat release source in the tunnel, which must be ejected to the ventilation air. The paper investigates both the heat load in a generic underground railway environment using a purposely-developed mathematical model and the potential methods of delivering cooling to such an environment. A theoretical analysis with the model has shown that the major contributor of heat to the tunnel is from the braking mechanism and that for the train carriage is from the passengers. The model has also shown that additional cooling to the existing rolling stock may be provided by cooling the tunnels within which they operate. The methods of cooling are evaluated from energy and comfort perspective and areas for further work that are required are described.