Page 42 IM-738
Where return air ducts are not required, it is recommended that
a sound absorbing T or L section be connected to the unit
return to reduce noise transmission to the occupied space.
Ductwork exposed to outdoor conditions must be built in
accordance with ASHRAE and SMACNA recommendations
and local building codes
.
Figure 49. Installing Ductwork
Installing Duct Static Pressure
Sensor Taps
For all VAV units, duct static pressure taps must be field
installed and connected to the pressure sensors in the unit. Sen-
sor SPS1 is standard; additional sensor SPS2 is optional. These
sensors are located at the bottom of the main control panel next
to terminal block TB2 (see “Control Panel Locations” on
page 12).
The duct static pressure sensing tap must be carefully located
and installed. Improper location or installation of the sensing
tap will cause unsatisfactory operation of the entire variable air
volume system. Following are pressure tap location and instal-
lation recommendations. The installation must comply with
local code requirements.
1. Install a tee fitting with a leak-tight removable cap in each
tube near the sensor. This will facilitate connecting a
manometer or pressure gauge if testing is required.
2. Use different colored tubing for the duct pressure (HI) and
reference pressure (LO) taps, or tag the tubes.
3. Locate the duct pressure (HI) tap near the end of a long
duct to ensure that all terminal box take-offs along the run
will have adequate static pressure.
4. Locate the duct tap in a nonturbulent flow area of the duct.
Keep it several duct diameters away from take-off points,
bends, neckdowns, attenuators, vanes, or other irregularities.
NOTICE
Installer must provide access in the ductwork for
plenum mounted controls.
On units with side discharge, access to plenum
mounted components becomes difficult once ductwork
is installed.
U n i t D u c t O p e n i n g
U n i t B a s e
9 . 7 6 "
4 . 5 8 "
R o o f C u r b
D u c t F l a n g e r
i n R o o f C u r b
F l e x i b l e
C o n n e c t o r
D u c t w o r k
NOTICE
Installer must provide access in the ductwork for
plenum mounted controls.
On units with side discharge, access to plenum
mounted components becomes difficult once ductwork
is installed.
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