A CFD simulation of indoor air contaminant on ventilation system in a bus passenger compartment

Good ventilation system in a bus passenger compartment is important for providing clean, healthy air and comfortable micro-environment for the passengers. Lack of fresh inside the bus passenger compartment due to poor ventilation system could increase the contaminants concentration which could affect the passenger’s health. This research reports findings of field measurement on the contaminants concentration of particulate matter (PM1) and carbon monoxide (CO) inside the passenger compartment of a university’s shuttle bus. The field measurements were conducted at the front, middle and rear locations of the passenger compartment. Measurements of PM1 and CO were done continuously in the morning, afternoon and evening. A CFD software was employed to develop a simplified three-dimensional model of the bus passenger compartment. Velocity and temperature boundary conditions were prescribed at the air supply diffusers, based on the measured data. Meanwhile, the contaminants concentration was prescribed at the door. Flow analysis was carried out using RNG k-? turbulent model for air flow, discrete phase and species transport for contaminants. Four cases of air supply diffuser locations namely mixing ventilations (MV3 and MV4), mixing ventilation with displacement ventilation (MV2+DV) and mixing ventilation with underfloor air distribution (MV2+UFAD) were examined. Two cases of air return grille locations namely three air return grilles (3RG) and four air return grilles (4RG) were also examined in this research. It was found from the field measurement that the contaminants concentration of PM1 and CO were high at the front location of the passenger compartment. This is due to insufficient ventilation inside the bus passenger compartment. Result of the CFD simulation shows that the MV2+DV, MV2+UFAD and 4RG of air supply diffuser and air return grille locations could reduce the contaminants concentration of CO and PM1 in the occupied zone inside the bus passenger compartment.

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