IBC AHU 800, Installation & Operating Manual

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2.3 Duct work
Ducting design and installation should adhere to
SMACNA and/or ASHRAE guidelines. Install
the ducting system to NFPA 90B (latest edition).
Adhere to the following:
Size the supply air plenum duct fitting to
the size of the appliance's supply air
opening, and extend for 3' above the
appliance.
Size the supply and return air ducting
according to ASHRAE standards or
equivalent.
Seal all joints and connections to prevent
air leakage from the ducting system.
Choose accessories that will not
excessively restrict the air flow and
create excessive pressure drop on the
system.
Note
When using medium and high velocity systems, ensure proper duct design for optimal
system performance and noise levels.
2.3.1 Sizing the ducts
The tables below provide examples of conventional duct types and sizing for the AHU appliance
running at low velocity. If using flex / insulated flex ducting, ensure that you allow for a higher
pressure drop.
Branch Duct - CFM at 0.25"wc external static pressure (galvanized duct)
Round CFM range
3" 20-30
4" 30-35
5" 55-65
6" 90-100
7" 135-160
Table 6 Sizing round galvanized duct for CFM range
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Section: Installation