B-SERIES INSTALLATION, OPERATION AND SERVICE MANUAL
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SECTION 15: DUCT CONSIDERATIONS
The air handler has been designed to operate at the
specific air volume and external static pressure that
was ordered (air handlers set-up to accept an
external static pressure (ESP) of 1 in wc (2.5 mbar).
This static pressure is generated by any additional
components that are added to the heater (i.e. inlet
hood, filter section, dampers, ductwork, discharge
heads, etc). Additional static pressure beyond that
ordered will affect the performance of the air handler
and lessen the air volume that can be delivered.
Proper engineering methods need to be employed
when calculating duct and component static pressure
(i.e. 2009 ASHRAE Handbook - Fundamentals,
Chapter 21). Accessory pressure drops are available
on Page 16, Table 9.
The system ductwork must comply with Sheet Metal
and Air Conditioning Contractors Nationals
Association (SMACNA) or any other recognized
standards.
As a general rule, all discharge ducts should have a
straight run of at least 3 hydraulic duct diameters
after the air handler before adding any fittings,
elbows, restrictions, etc. Return ducts should have
the same straight r
un before attaching to the unit.
Hydraulic duct diameter for round ducts in inches:
Dh = d
Dh: hydraulic diameter
d: round duct inside diameter
Hydraulic duct diameter for rectangular ducts (in
inches):
Dh = (2*H*W)/(H+W)
Dh: hydraulic diameter
H: rectangular duct inside height
W: rectangular duct inside width
The air handler is not designed to support the weight
of ductwork. Ductwork must be constructed in a
fashion that is self-supporting. Ductwork should be
straight, elbows should be minimal and any
transitions should be smooth.
Depending on the options ordered with the air
handler, flanges (either external or internal) may be
provided to facilitate connection of ductwork. In
cases where flanges are not provided, flat surfaces
on the exterior skin of the air handler are pro
vided to
facilitate connection of ductwork.
15.1 Inlet Duct Work
Inlet duct work height and width must be no smaller
than the air handler inlet height and width and supply
only fresh air to the air handler. (See Page 11,
Section 5 for inlet dimensions).
15.2 Return Duct Work
Inlet duct work height and width must be no smaller
than the air handler inlet height and width and supply
only fresh air to the air handler. (See Page 11,
Section 5 for inlet dimensions).
15.3 Discharge Duct Work
Refer to Page 73, Table 10 for minimum discharge
duct sizes by model. Refer to Page 73, Table 11 for
discharge duct size required for connecting to heater
(BD or RD), these dimensions provide clearance for
duct flange to blower mounting bolts.
Cut/Pinch Hazard
Wear protective gear
during installation,
operation and
service.
Edges are sharp.
Falling Hazard
Use proper safety
equipment and prac-
tices to avoid falling.
WARNING
Failure to follow these instructions can result
in death, injury or property damage.
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