Reducing indoor air contaminants inside a campus bus passenger compartment

Abstract

Good ventilation system is important to provide fresh air and comfortable environment for passengers. Lack of fresh air inside a bus compartment may cause various illnesses such as headache, asthma, cardiovascular and lung cancer. Two factors influence the ventilation system effectiveness namely the arrangement of air supply diffusers and the air return grilles. This thesis presents a study on air contaminants inside a university’s bus passenger compartment. The goal is to find a suitable ventilation arrangement that can reduce the concentration of the air contaminants. First a field measurement was carried out on a selected bus to measure the air contaminants at the front section, middle section and rear section. The contaminants include carbon monoxide, carbon dioxide, formaldehyde and particulate matter. Then computational fluid dynamics flow analyses were carried out on simplified model of the bus compartment employing renormalization group k-ε model for air flow, species transport for gases and discrete phase for particles. Five cases of ventilation arrangements were considered namely displacement ventilation with two air return grilles, underfloor air distribution with two air return grilles, mixing ventilation with four air return grilles, displacement ventilation with four air return grilles and underfloor air distribution with four air return grilles. It was found from the field measurements that the concentration of carbon monoxide, carbon dioxide, formaldehyde, particulate matter 1, particulate matter 2.5 and particulate matter 10 were 7 ppm, 1102 ppm, 0.18 ppm, 52 μg/m3, 52 μg/m3 and 51 μg/m3, respectively. Results of flow simulations show that the underfloor air distribution with four air return grilles is able to reduce the contaminants concentration inside the passenger compartment. On average, the concentrations of carbon monoxide, carbon dioxide, formaldehyde, particulate matter 1, particulate matter 2.5 and particulate matter 10 were reduced by about 40%, 10%, 38%, 37%, 33% and 30%, respectively.