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Ductwork and attenuation
Discharge ductwork is normally used with these condi-
tioners. Return air ductwork may also be required, but will
require field installation of a return air duct collar/2" (51mm)
filter rack kit.
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
flexible connector at the unit, a non-insulated transition
piece to the full duct size, a short run of duct, an elbow
without vanes, and a trunk duct teeing into a branch circuit
with discharge diffusers as shown in Figure 3. The transition
piece must not have an angle greater than 30° or severe
loss of air performance can result. Do not connect the full
duct size to the unit without using a transition piece down
to the size of the discharge collar on the unit. With metal
duct material, the sides only of the elbow and entire branch
duct should be internally lined with acoustic insulation for
sound attenuation. Glass fiber duct board material is more
absorbing and may permit omission of the flexible
connector.
The ductwork should be laid out so that there is no line
of sight between the conditioner discharge and the distrib-
ution diffusers.
Return air ducts can be brought in through a wall grille
and then to the unit. The return duct system will normally
consist of a flexible connector at the unit and a trunk duct
to the return air grille. With metal duct material, the return
air duct should be internally lined with acoustic insulation
for sound attenuation. Glass fiber duct board material is
more absorbing and may permit omission of the flexible
connector.
Return air ductwork to the unit requires the optional
return air duct collar/2" (51mm) filter rack kit. See Figure 4
and 5. The kit can be installed for face side or bottom filter
removal. The flexible connector can then be attached to the
1" (25mm) duct collar.
Do not use sheet metal screws directly into the unit
cabinet for connection of supply or return air ductwork,
especially return air ductwork which can puncture the drain
pan or the air coil.
Ventilation air
Outside air may be required for ventilation. The temper-
ature of the ventilation air must be controlled so that mixture
of outside air and return air entering the conditioner does
not exceed 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. Introduce outside
air into each return air plenum chamber reasonably close to
the conditioner air inlet. Do not duct outside air directly to
the conditioner inlet. Provide sufficient distance for thor-
ough mixing of outside and return air. See “Operating limits”
on page 8.
Square Elbow
(Both Sides
Internally Lined
With Acoustic
Insulation)
Trunk Duct
2 ft. x 2 ft.
Diffuser
Discharge
Collar
Heat Pump
Duct
Transition
Branch Duct
(Internally Lined)
Figure 3.
Figure 4. Sizes 007 thru 048 Optional 2" Return Air Duct
Collar Filter Rack
Figure 5. Size 060 Optional 2" Return Air Duct Collar
Filter Rack
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