Heat deficit mitigation strategies for elevated rail stations in cold regions of China based on thermal comfort assessment

The elevated station of rail transit is different from the conventional underground stations; such buildings are complex in space form. In the cold region in winter, the elevated station is greatly affected by the outdoor climate environment, and passengers feel cold, so it is urgent to improve its thermal environment. In this paper, taking the Xi'an rail transit elevated stations in China as the research objects, the internal environment investigation and thermal comfort assessment of the elevated station were carried out by using subjective survey questionnaire combined with field monitoring. The thermal design temperature in elevated stations in winter in cold areas was determined by calculating change process of passengers' heat deficit rate (HDR). And then the heat deficit mitigation strategy of elevated stations in winter in cold areas was put forward, and the rationality and reliability of the strategy were verified Through the corresponding simulation. The field measurement results show that the temperature of the investigated stations is lower than the threshold of cold sensation, and the air flow rate is significant. The temperature of side station is lower than that of island station. The questionnaire results show that passengers who want to reduce the wind speed generally vote for the temperature to increase simulta-neously. By analysing the change of thermal deficit rate in the whole process of passengers entering the station, it is found that for two kinds of stations in the platform layer the heat deficit rate reaches a peak, which is-50.7 W/m2 and-53.2 W/m2, respectively. It is found that the appropriate temperature range to meet the re-quirements of thermal comfort should be 14.8 degrees C-20.8 degrees C. The simulation results indicated that the temperature in platform can be raised from the current 3.6 degrees C-6.8 degrees C-11.3 degrees C-13.6 degrees C by using the fully enclosed platform combined with thermal insulation system proposed. In order to reach to the minimum requirement of 14.8 degrees C in the station in winter, the station temperature can be further improved by optimizing the enclosure structure or installing additional air conditioning system to reach the comfort requirement. This study provides reliable basic data for the mitigation of heat deficit and developing a standard design for elevated stations.