JOHNSON CONTROLS
92
FORM 102.20-N1
ISSUE DATE: 7/06/2016
SECTION 3 - HANDLING, STORAGE, AND INSTALLATION
FIGURE 143 -
DUCT ARRANGEMENT FOR FLANGE AND RAW EDGE DUCTS
LD014087
Detail A
Sheet Metal Screw
Gasket Or Sealant
Flanged Duct
Raw Edge Duct
Gasket
Or
Sealant
The performance ratings of coils will be met only if the
airflow is uniform over the face of the coils. High air
velocity spots on the coil may cause carryover of mois-
ture from the coil. High or low air velocity areas of
the coil will not deliver the published ratings. The duct
connections must be designed to provide for uniform
flow of air across the face of the coil. The entering duct
must provide a smooth transition from any high veloc-
ity effects. Stratifications of outside and return air, es-
pecially 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 generated
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.
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 XTO 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
.
