Ventilation Improvement in a Non-AC Bus

Ventilation is a crucial factor affecting passenger comfort in any vehicle. In a non-air-conditioned bus, ventilation caters to the dual requirement of fresh breathing air as well as providing a cooling sensation by enhanced evaporation of sweat. The higher the velocity of air around the passengers, the greater the cooling effect experienced by them. The ventilation mechanism of a non-air-conditioned bus is primarily the air flow through the windows due to relative motion between the bus and the air around it. This paper describes studies carried out to identify the right combination of open windows which would provide optimum air flow at the passenger head level plane in a bus. A bus model with 12 windows, 6 on each side is used for the study and air velocity at certain points in the head level plane, arising out of different combination of window openings is evaluated using CFD. The minimum value of velocity observed among the points, which is indicative of the minimum level of comfort provided by the combination, is compared for different combinations of openings and the optimum identified. Since a comparison of all possible combinations would involve evaluating 3¹² CFD runs, Design of Experiments (DOE) is used to obtain the optimum using a reduced number of analyses. Through this study it is attempted to place windows only at few strategic locations that would contribute to optimum air flow at all points within the bus by eliminating the non contributing windows without reduction in passenger comfort, thereby changing bus design philosophies and providing greater freedom in bus design. The optimum configuration of windows was found to provide ∼17% reduction in window area.