2-3。5 Step 5。  Determine the exhaust volumetric flow, in cubic meters per second (m3/s) [cubic feet per minute (cfm)], required to maintain the capture velocity determined in paragraph 2-3。4。

2-3。6 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。

2-3。7 Step 7。  Size ductwork using the balance by design or the blast gate method。  Maintain the required minimum transport velocity throughout the system。

2-3。8 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。

2-4 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。

2-4。1 Ductwork。  In addition to the recommendations of the ACGIH IV Manual, consider the following when designing a ventilation system。

a。 Specify duct gage, reinforcement schedule and hanger design and spacing, in accordance with SMACNA RIDCS, Round Industrial Duct Construction Standards for round duct and SMACNA RTIDCS, Rectangular Duct Construction Standards for rectangular duct。

b。 Install clean-out doors in ductwork that conveys particulate material such as wood dust or blasting grit。 Mount clean-out doors on top half of horizontal runs near elbows, junctions, and vertical runs。

2-4。2 Fans

2-4。2。1 Selection。  Except where specified below, fan selection criteria for replacement air fans and exhaust air fans are identical。

a。 Select exhaust system industrial fans that meet design pressure and volume flow rate requirements and have the AMCA-certified performance seal。 The design pressure requirement must account for any system effects caused by non-uniform airflow into or out of the fan。 See AMCA 201, Fans and Systems for more information on system effects。 Specify a fan class that is appropriate for the design operating point。 Do not select fans with forward curved blades。

b。 When selecting fan capacity, consider if the process room pressure will be positive, negative or neutral with respect to the external areas。 Select a fan that will provide the necessary volumetric flow rate to maintain the desired process room pressure。 Ensure that all sources of exhaust air are considered when selecting fan capacity。 See paragraph 2-

4。5 for more details。

c。 Specify fan shafts that have a uniform diameter along the entire length。 Use bearings that are rated with an average life of 200,000 hours。

d。 Select only energy efficient motors。 Select the motor to handle cold startup amperage for nonstandard air processes。

e。 Specify vibration-isolating couplings at the fan inlet and outlet。 Mount all fans on vibration isolating bases。