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Ductwork & Attenuation
Discharge ductwork is normally used with these condition-
ers. Return air ductwork may also be required.
All ductwork should conform to industry standards of
good practice as described in the ASHRAE Systems Guide.
The discharge duct system will normally consist of a
flexible connector at the unit, a transition piece to the full
duct size, a short run of duct, an elbow without vanes, and
a trunk duct teeing into a branch duct with discharge dif-
fusers as shown in Figure 5. The transition piece must not
have angles totaling more than 30° or severe loss of air per-
formance 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 fibrous insulation for sound
attenuation. Glass fiber duct board material is more absorb-
ing and may permit omission of the canvas connector.
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 through a low side
wall filter-grille and then up through the stud pieces to a
ceiling plenum or through air ceiling filter-grilles. The ceiling
filter-grille must not be placed directly under the
conditioner.
Return air ductwork can be connected to the standard
filter rack. See Figure 6 (side filter removal shown). The fil-
ter rack can be installed for bottom filter removal or side fil-
ter removal by locating the brackets. For side filter removal
the brackets should be located on the bottom, left side, and
top. For bottom filter removal the brackets should be
mounted on the left side top and right side with the spring
clips supporting the filter.
Do not use sheet metal screws directly into the unit cab-
inet for connection of supply or return air ductwork, espe-
cially return air ductwork which can hit the drain pan or the
air coil.
Figure 5.
Figure 6. Filter rack/return air duct collar
2x2 Ft.
Diffuser
(Example
Only)
Branch Duct
Internally Lined
With Acoustic
Fibrous
Insulation
Trunk Duct
Square Elbow
Canvas
Collar
Heat
Pump
Transformation
Piece
Discharge Collar
On Heat Pump
Both Sides Internally Lined With
Acoustic Fibrous Glass Insulation
Suggested Duct Layout For
Multiple Diffuser Application
Standard 2" (51 mm)
for sizes 070 thru 120
Ventilation may require outside air. The temperature of the
ventilation air must be controlled so that mixture of outside
air and return air entering the conditioner does not exceed
conditioner application limits. It is also typical to close off
the ventilation air system during unoccupied periods (night
setback).
The ventilation air system is generally a separate build-
Ventilation Air
ing subsystem with distribution ductwork. Simple introduc-
tion of the outside air into each return air plenum chamber
reasonably close to the conditioner air inlet is not only ade-
quate, but recommended. 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 10.
(31 pages)
(58 pages)
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