Effects of air supply diffusers and air return grilles layout on contaminants concentration in bus passenger compartment

Abstract

Ventilation system in a bus is employed to provide good indoor air quality and thermal comfort for passengers. Poor ventilation system will increase the concentration level of air contaminants which could affect the passenger’s health. The presence mixing ventilation system used in many buses is not efficient in removing the air contaminants from the passenger compartments. This article presents a study on the effects of using different ventilation setups on the concentration level of gases and particulate matters inside a passenger compartment of a university’s shuttle bus. The goal is to find a suitable layout of the air supply diffusers and air return grilles that would lower the concentration level of contaminants inside the passenger compartment. Field measurements were carried out to quantify the concentration of gases (carbon monoxide, carbon dioxide and formaldehyde) and particulate matters (PM1, PM2.5 and PM10). The measurements were done at the front section of the bus compartment, close to the front door. The data were acquired in the morning, afternoon and evening hours during a clear and sunny day. The bus travelled along an in-campus road with no passengers. A simplified three-dimensional model of the bus compartment was developed using computational fluid dynamics software. Flow analyses were carried out to predict distribution of gases and particulate matters concentration. The concentrations of carbon dioxide, carbon monoxide, formaldehyde and particulate matters obtained from the field measurements were used as boundary conditions and for validating the computational model. A parametric study was carried out to identify a suitable layout of air supply diffusers and air return grilles that would lower the concentration level of the air contaminants. Two types of ventilation systems were considered namely a displacement ventilation and an underfloor air distribution. Results show that the underfloor air distribution system is more effective in reducing the concentration level of gases and particulate matters inside the passenger compartment compared to the displacement ventilation system.