Healthier passenger rail: Influence of the ricirculation system on the spreading of exhaled particles in a passenger train

Abstract

Airborne, potentially contaminant-laden exhaled particles can reach the other passengers either directly, i.e., transported by the air flow within the passenger car from the source to the receiver, or indirectly, i.e., by being recirculated through the heating, ventilation and air-conditioning (HVAC) system. The rate of particles which are recirculated is depending the recirculation rate of the HVAC system, the applied filter, the ducting system and other sub-systems. The presented scientific approach of setting well-defined removal rates of the recirculation system in combination with a generic but realistic long-distance train geometry and a state-of-the-art ventilation system is one of the main advantages of our research. Our approach allows to directly evaluate the influence of the different recirculation rates (in terms of particle removal) on the resulting local particle concentrations within the passenger compartment. We can evaluate the effect of the indirect compared to the direct particle transmission from the particle-exhaling ‘source’ passenger to the breathing zones of the other passengers. We numerically investigated the dispersion of aerosols in a full-size model of a recirculated-air train passenger car with two ventilation configurations that aimed at studying particle concentration and residence time. Although a noticeable increase in the average residence time was found, it does not lead to higher local concentration, since this increase is due to particles that are returned and dispersed throughout the car.