Simulation Study of Seasonal Variations Impact on Fire Detection in Subway Carriage Supply-Return Airflow Environments

Objective Subway carriage fire accidents often cause heavy loss of life and property, while the early detection of subway carriage fire can effectively ensure passenger′s lives. It is necessary to conduct research on this issue in different seasons under the environment of supply-return air. Method A full-scale subway carriage numerical simulation model and an HVAC（heating, ventilation and air conditioning） system including an air supply system, an exhaust system, and a return air system is established. Referring to three scenarios of natural ventilation, normal operation ventilation in different seasons, and carriage fires, the influence of HVAC system supply-return air in different seasons on the subway carriage airflow field and the fire early detection is analyzed. Result ＆ Conclusion The characteristics of the subway carriage internal airflow field vary significantly under different seasonal operational ventilation. In the winter wind mode, heating is supplied to the carriages, resulting in stratified circulation of air with different temperatures between the upper and lower layers of the carriage during the stable period. Conversely, in the summer wind mode, cooling is provided to the interior of the carriages, resulting in a relatively uniform airflow pattern during the stable period compared to the winter wind mode. During a fire incident, smoke generated in the summer wind mode exhibits a faster smoke layer descent rate, while in the winter wind mode, the smoke spreads in a faster speed towards the sides of the carriages. As seen in the established model, the summer wind mode requires a shorter fire response time compared to the winter wind mode.