EXHAUST SYSTEMS
The best exhaust systems should be of shortest duct length and the fewest elbows / bends. Duct size, length, and number of elbows affect static pressure loss and blower efficiency. Ideally, each fume hood should have its own exhaust system to maximize hood flexibility and avoid danger of explosion due to mixing of chemical vapors and backdraft issues from other hoods.
Normally manifold ductwork designs are used to clustered fume hoods, with duct and blower have been sized properly. In the manifold designs, individual hood should have dampers to balance the exhaust flow. Rigid Polypropylene + Fiber Reinforced Plastic (PP+FRP) exhaust duct system is accepted as a most suitable for chemical fume hood exhaust duct material. The smooth interior surface reduces static pressure loss and chemical waste build up, and Polypropylene (PP) is extremely resistant to a wide variety of acids and solvents.
For low duty application metal breed flexible Poly Vinyl Chloride (PVC) duct provides more suitable and can significantly reduce installation costs. When planning exhaust ducting, duct size, length, number of bends, and exhaust material must be considered.
It is recommended that exhaust blowers be located at the end of the ducting which is typically either roof mounted, or wall mounted. This ensures a negative pressure throughout the ventilation system.
By keeping the exhaust duct as short and as straight as possible, the total resistance will be reduced and by keeping the diameter of the duct correctly sized to the flow volume, noise and static pressure can be reduced.