Form PA102.20-N1
95
Installation & Assembly Manual │
PACE
SECTION 3 - HANDLING, STORAGE, AND INSTALLATION
Issue Date: 07/03/2018
3
Raw or Straight Edge Duct or Sleeves
The duct opening on the AHU is located in a panel
about 2 in. thick, which is suitable for attaching ducts.
If access is not available from the inside of the AHU,
access may have to be gained from inside of the duct
or sleeve.
Connect the raw or straight edge ducts with the self-
drilling screws directly to the AHU with a gasket or seal-
ant between the AHU and the duct flange as shown in
Detail A
Sheet Metal Screw
Gasket Or Sealant
Flanged Duct
Raw Edge Duct
Gasket
Or
Sealant
LD014087
Figure 157 -
Duct Arrangement for Flange and Raw Edge Ducts
In applications where sound and vibration transmis-
sions may be objectionable, good acoustical engi-
neering practices must be incorporated in the system
design. On AHUs with return fans, it is important to
consider the effects of sound transmission into the air-
conditioned space.
When a AHU is used with a ceiling plenum return
air system, sound may be transmitted from the AHU
through the ceiling to the air-conditioned space. For
such applications, install a sound absorption chamber
near the AHU return air inlet. Various reference sourc-
es are available regarding acoustic design.
Installing Top Discharge Outdoor AHU Duct
For outdoor PAO top duct connection, the installer is
responsible for sealing the duct to the roof panel. The
installer should not seal the duct to the unit opening.
Installing Front and Rear Discharge
Outdoor AHU Duct
Use the following instructions to install the front and
rear discharge outdoor AHU duct.
• Building roof penetrations by ducts should utilize
counter flashed curbs as shown in
The performance ratings of coils will be met only if the
airflow is uniform over the face of the coils. High air ve-
locity spots on the coil may cause carryover of moisture
from the coil. High or low air velocity areas of the coil
will not deliver the published ratings. The duct connec-
tions must be designed to provide for uniform flow of air
across the face of the coil. The entering duct must pro-
vide a smooth transition from any high velocity effects.
Stratifications of outside and return air, especially where
below freezing outside air enters, must be avoided to
prevent coil freeze-up or nuisance low limit trips.
Sound and Vibration Transmission
All roof-mounted AHUs generate some sound and vi-
bration, which may or may not require special treat-
ment of the air-conditioned space. The noise gener-
ated by the AHU depends on the following:
• Speed of the fan,
• Amount of air the fan is moving,
• Fan type, and
• Static efficiency of the fan.
