Page 6 of 24 / IM 439
Duct Collar Side
Duct
Collar
Filter
Rack
Ductwork and Attenuation
Discharge ductwork is normally used with these conditioners.
Return air ductwork may also be required but will require field
installation of a return air duct collar.
All ductwork should conform to industry standards of good
practice as described in ASHRAE Systems Guide.
The discharge duct system will normally consist of a flex-
ible connector at the unit, a transition piece to the final duct
size, a short run of duct, an elbow without vanes and a trunk
duct tee’d into branch ducts with discharge diffusers as shown
in Figure 10. Transition piece must not have angles totalling
more than 30 degrees or severe loss of air performance can
result.
All units have multiple fan outlets. A single duct can en-
close all the openings as shown in Figure 10; however, the
preferred method for minimum static pressure loss would be
individual ducts at each outlet connected to a larger duct down-
stream.
For minimum noise transmission, the metal duct material
should be internally lined with acoustic fibrous insulation.
The ductwork should be laid out so that there is no line of
sight between the conditioner discharge and the distribution
diffusers.
Return air ducts can be brought in adjacent to the return
air of the conditioner. Typically, the equipment room becomes
the common return air plenum.
Do not insert sheetmetal screws directly into the unit cabi-
net for connection of supply or return air ductwork, especially
return air ductwork which can hit the drain pan or the air coil.
Ventilation Air
Outside air may be required for ventilation. The temperature
of the ventilation air must be controlled so that mixture of out-
side air and return air entering the conditioner does not ex-
ceed conditioner application limits. It is also general practice
to close off the ventilation air system during unoccupied peri-
ods (night setback).
The ventilation air system is generally a separate build-
ing subsystem with distribution ductwork. Simple introduction
of the outside air into each return air plenum chamber rea-
sonably close to the conditioner air inlet is not only adequate,
but recommended. Do not duct outside air directly to the con-
ditioner inlet. Provide sufficient distance for thorough mixing
of outside and return air
(see Operating Limits on page 9).
Optional Duct Collar and 2" (51 mm)
Filter Rack
The optional duct collar kit is used to facilitate connection of
return air duct to the unit. The duct collar kit can be used in
conjunction with the standard 1" (25 mm) thick filter rack or
the optional 2" (51 mm) filter rack.
The 2" (51 mm) filter rack facilitates the installation of 2"
(51 mm) thick filters for side removal. The 2" (51 mm) filter
rack replaces the existing 1" (25 mm) filter rack and does not
require the use of the optional return air duct collar.
The kits are installed as follows:
1.
Remove all filters, filter racks and brackets. Save all
screws. Discard bracket end.
2.
Attach top duct collar in conjunction with top filter rack
with truss head screws.
3.
Attach bottom duct collar and filter rack.
4.
On single compressor units, attach two flanges using four
(4) #8 truss head screws provided.
5.
Attach center support in original location.
6.
Locate and attach center filter racks using screws pro-
vided.
7.
Attach duct collar sides using eight (8) #10 sheetmetal
8.
No point in the drain system may be above the drain
connection of any unit.
9.
Automatic flow controlled devices must not be installed
prior to system cleaning and flushing.
10. A high point of the piping system must be vented.
11.
Check local code for the need of dielectric fittings.
Figure 8. Assembly detail
Center Support
Chassis
Door End
Duct Collar Side
Center Filter Racks
Side Flanges
Top Duct Collar
Top Filter Rack
Filters
Figure 9.
