25 October 2004
consider how the system being designed might affect the performance of any existing
processes, industrial ventilation systems or HVAC systems.
Step 2. Consider how the facility is to be used or expanded in the future.
It may be possible to initially specify fans that are capable of handling future needs at
minimal increased cost.
or design the exhaust hood that best suits the work piece
or operation. Design the exhaust hood to enclose the work piece or operation as much
as possible. This will reduce the ventilation rates required to provide contaminant
control. This UFC provides optimum exhaust hood designs for many of the operations
Step 4. Determine the capture velocity required to control generated
contaminants. Capture velocities in this UFC are specified assuming there are no cross
drafts or turbulence that adversely affects the capture efficiency. Reduce potential for
cross drafts or turbulence near a given exhaust hood by properly locating and designing
the hood with baffles, and also by designing the replacement air system to complement
the exhaust system.
Step 5. Determine the exhaust volumetric flow, in cubic meters per
second (m /s) [cubic feet per minute (cfm)], required to maintain the capture velocity
determined in paragraph 2-3.4.
Step 6. Create a line drawing of the proposed system. Include plan and
elevation dimensions, fan location and air cleaning device location. Identify each hood,
branch duct and main duct sections.
Step 7. Size ductwork using the balance by design or the blast gate
method. Maintain the required minimum transport velocity throughout the system.
Step 8. Determine requirements for replacement air. Based on the
process, determine if the room should be under slightly negative, neutral or slightly
positive pressure with respect to the surrounding area. The surrounding area can be
either outside the building envelope or an adjacent room or hallway. Determine if
tempered replacement air is needed.
DESIGN CRITERIA. Several design criteria are common to all industrial
ventilation systems; use the ACGIH IV Manual for primary guidance. See paragraphs 2-
4.1 through 2-4.5 for additional guidance. Chapters 3 through 10 provide design
guidance for specific types of facilities.
Ductwork. In addition to the recommendations of the ACGIH IV Manual,
consider the following when designing a ventilation system.