Types of Fume Hoods Based on Air Volume
Open by-pass fume hood
- Designed for operation on constant air volume exhaust systems
- The air by-pass provides for an alternate route for air to enter the hood as the sash is closed
- The size of the by-pass is set so that, as the sash is closed, the velocity of the air increases to no more than 3.5 times the velocity with the sash fully open.
Low constant volume fume hood
- These fume hoods use a restricted sash opening or a lower face velocity, or both to reduce the exhaust quantity of air
- Traditionally, such fume hoods can reduce the exhaust CFM from 40% to 60% from Open By-pass levels.
Restricted by-pass fume hood
- Designed for operation on variable air volume (VAV) exhaust systems when used with a fume hood face velocity controller
- By reducing the amount of air exhausted, as the sash is lowered, a constant face velocity is maintained, exhausting less air than a Constant Volume hood.
Auxiliary air fume hood
- Auxiliary Air fume hoods are Constant volume hoods designed for use when it is not feasible to introduce the required makeup air through the room ventilation system.
- Up to 70% of the exhaust volume can be supplied through an auxiliary air chamber mounted above the hood.
- These hoods require a separate ducted fan system for the supply of the auxiliary air.
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