ABSTRACT
The connecting link between the hood and fan is the ductwork. It serves the dual function of controlling the rate of air flow and conveying the contaminant-laden air to the fan suction and away as heretofore mentioned. Air cleaning is a specialty in itself, and the designer should refer to the literature on the subject. Management is attracted by recirculation systems as a way to conserve fuel and to avoid expensive makeup air systems. Where recirculation is permissible, it could be economically feasible to install high-efficiency air cleaning with recirculation where air pollution requirements would allow low-efficiency air cleaners and discharging to the outside. Fans are the mechanical air-moving devices which make most industrial exhaust systems operate. Although the ventilation design engineer is generally concerned with fan designs, he should know and understand enough of their theory and performance characteristics to be able to select, evaluate, and modify industrial exhaust fans.
