CFD Analysis of the Effects of Opening of Doors on the Carbon Dioxide Concentration in Public Utility Buses

Abstract: High levels of carbon dioxide concentration pose a significant problem in the Philippines, especially in vehicles where commuters spend a majority of their time mainly due to heavy traffic. Longer travel times and overcrowding expose the commuters to unsafe levels of carbon dioxide (CO2) concentrations, which can lead to dizziness and nausea. Therefore, this paper investigates the CO2 concentration distributions inside a typical fully air-conditioned bus with fully closed windows, where fresh air is introduced via the ceiling ventilation system and through door openings at bus stops, using Computational Fluid Dynamics (CFD). Two ventilation modes were studied: fresh air mode and recirculation mode. Data were collected during a 30-second time period when the doors are opened. Between the two ventilation modes, recirculation mode yields a higher average CO2 concentration of 2900 ppm compared to fresh air mode, which has an average CO2 concentration of 1200 ppm. Furthermore, the results show that there is a diminishing effect on the ventilation provided by opening the doors the farther the location is from the door. Lastly, during the sampling duration, the average CO2 concentration decreases in fresh air mode by 56 ppm, while it continues to increase at a slower rate of 1-2 ppm in recirculation mode. Keywords: indoor air quality, carbon dioxide level, computational fluid dynamics, public utility bus