This study develops a new passive ventilation system for a passenger train. This ventilation system comprises a supply air system and an exhaust air system; it improves indoor air quality and uses only the pressure field generated by the movement of the train as its energy source. Air from the supply system enters the front exterior of the train and exits at the lower part of the interior of the train. Air from the extraction system enters the upper part of the interior of the train and exits at the rear exterior of the train. In the study, a train comprising five rooms was considered. Each room is equipped with 16 seats and two tables, accommodating 16 passengers.

The numerical model uses a system of integral energy and mass balance equations. In passive ventilation, the second-order energy integral equations and the first-order mass integral equations are considered to evaluate the airflow rate. The energy integral equations account for kinetic, potential, pressure, and local and continuous energy losses.

The airflow rate, which influences the internal carbon dioxide concentration, is considered in the indoor air quality evaluation. However, the airflow rate depends on the vehicle velocity. As the vehicle velocity increases, the internal airflow rate also increases.

According to the results, a vehicle velocity above 20 m/s generally ensures acceptable indoor air quality. However, extreme train rooms present a higher airflow rate than the central room. The duct design, equations system, and more details are presented in the short paper.