Fiala model-based evaluation of metro thermal comfort and energy performance under impinging jet ventilation

Metro carriage environments are characterized by high occupant density and significant operational heat accumulation, leading to pronounced thermal discomfort and underscoring the need for advanced ventilation solutions. This paper addresses this by proposing an impinging jet ventilation (IJV) configuration and comparing its efficacy in optimizing thermal comfort against a standard mixing ventilation (MV) configuration. The fidelity of the numerical simulations was verified against full-scale experiments conducted in an actual metro vehicle. Thermal comfort at multiple positions within the cabin was evaluated by coupling the Fiala Thermoregulation model with the Equivalent Homogeneous Temperature model. Manikin surface temperature, spatial air temperature, flow-field characteristics and energy consumption were systematically contrasted between the two ventilation strategies. The principal findings are as follows: compared with the MV configuration, the IJV configuration systematically improved and optimised thermal comfort across the entire enclosure. Maximum reductions in the Fiala Dynamic Thermal Sensation and the Fiala Predicted Percentage Dissatisfied indices reached 47.88 % and 49.45 %, respectively, across all assessed manikins. Both manikin surface temperatures and global air temperatures were effectively lowered, sustaining satisfactory thermal comfort for seated and standing passengers while maintaining the temperature difference between head and ankle regions below 3 °C. Spatial discrepancy of the overall flow field was attenuated, fluctuations in the airflow surrounding occupants were diminished, and energy expenditure was reduced. Relative to the MV configuration, the IJV configuration enhanced thermal comfort and simultaneously decreased energy consumption by approximately 25.63 %. © 2025 Elsevier B.V.