JOHNSON CONTROLS
91
SECTION 3 - HANDLING, STORAGE, AND INSTALLATION
FORM 102.20-N1
ISSUE DATE: 7/06/2016
3
DUCT CONNECTIONS
The duct must have positive seal to the AHU openings.
Outdoor base rails are available in 3, 6, 8, or 10 in.
height. It's the contractor's responsibility to provide the
ductwork, which includes the base rail height, and sup-
port it independently from the AHU.
Duct Connection Guidelines
The duct connection guidelines are as follows:
•
Duct connections to the AHU may be made di-
rectly except when the AHU has external isola-
tion. Then the duct connections should be made
with flexible material, and be installed so they are
sufficiently loose.
•
Duct connections should be designed and installed
according to AMCA Standards 200 and 201, at a
minimum.
•
Duct turns and transitions must be made carefully
to hold friction loss to a minimum. Avoid short
turns. Duct elbows should contain splitters or
turning vanes.
•
The effective duct length connected to the fan or
AHU discharge should run in a straight line for at
least 2.5 equivalent discharge diameter for up to
2500 FPM fan outlet velocity and one additional
diameter for each additional 1000 FPM fan outlet
velocity.
•
Ductwork should be no greater than 105.5% or no
less than 85.5% of the discharge area. The slope
of the transition elements should not be greater
than 15% for converging elements, or greater than
7% for diverging elements.
• To find the equivalent discharge diameter, use
the following equation, where a = height, and b =
width of the discharge:
EDD = 4ab/�
•
A duct turn should be in the same direction as the
fan rotation as shown in
Never deadhead the discharge into the flat surface
of a plenum.
FIGURE 142 -
RECOMMENDED DISCHARGE DUCT
ARRANGEMENT WHEN TURNS ARE REQUIRED
LD06335
Note: Make Turns In
The Same Direction
As Fan Rotation
Air
Flow
Air
Flow
Air
Flow
Air
Flow
Effective Duct Length
Turning Vanes
Flanged Duct or Sleeves
To use flanged ducts or sleeves, make sure there is ac-
cess on all four sides to fasten the flange completely.
Connect the flanged ducts with self-drilling screws di-
rectly to the AHU with a gasket or sealant between the
AHU, and the duct flange as shown in
. A flange may be dropped through the open-
ing, if there is access to seal and fasten the flange to the
AHU's interior surface.
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
sealant between the AHU and the duct flange as shown
in