Installation manual

Page 22 IM-487
Installing Ductwork
On bottom-supply/bottom-return units, the installing contrac-
tor should make an airtight connection. Attach field fabri-
cated duct collars to the bottom surface of either the roof
curb's duct flange or the unit's duct opening if a McQuay roof
curb is not used. Do not support the total weight of the duct-
work from the unit or these duct flanges. Refer to Figure 23.
Units with optional back return, side discharge, or end discharge
(on RFS units) all have duct collars provided. The discharge
duct collars on a side discharge unit are exposed by removing
the plenum section access door and the door gasketing.
Use flexible connections between the unit and ductwork to
avoid transmission of vibration from the unit to the structure.
Design ductwork per ASHRAE and SMACNA recommenda-
tions to minimize losses and sound transmission.
Where return air ducts are not required, connect a sound
absorbing T or L section to the unit return to reduce noise
transmission to the occupied space.
Build ductwork exposed to outdoor conditions in accordance
with ASHRAE and SMACNA recommendations and local
building codes
.
Figure 23. 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.
Sensor 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 Loca-
tions” on page 9).
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
installation 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.
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
CAUTION
Fragile sensor fittings.
May damage pressure sensor.
If tubing must be removed from a pressure sensor fitting,
use care. Do not wrench the tubing back and forth to
remove or the fitting may break off.