32
Step 11 — Perform Field Modifications
DUCTWORK
Bottom Return Units (50A2,A3,A6,A7) Field-Modified for
Side Return
The 50A2,A3,A6,A7 units with bottom return air connec
-
tions may be field-modified to accommodate side return air
connections.
Conversion to horizontal return requires that the bottom return
openings of the unit must be sealed with airtight panels capable of
supporting the weight of a person. The return ductwork connec
-
tion locations on the side of the unit are higher than normal (31 in.
high). Unit-mounted power exhaust or barometric relief cannot be
used because return air ductwork will cover the power exhaust or
barometric relief installation locations. Power exhaust or baromet
-
ric relief may be installed in the return air ductwork.
To convert the unit, perform the following:
1. Seal the bottom return openings of the unit with airtight pan
-
els capable of supporting the weight of a person.
2. Remove the panels located below the economizer outdoor-air
dampers. These openings will be used for the return-air
ductwork. There are 2 panels on 50A3,A6,A7020-050 units.
There are 3 panels on 50A2,A3,A6,A7060 units. These open
-
ings are normally used for power exhaust or barometric relief.
3. Run the return air ductwork up to the openings. One single
duct is recommended to connect to the unit over the return air
openings. See Fig. 43. The return duct must incorporate a
minimum
3
/
4
-in. flange for connection to the unit cabinet. The
unit does not have duct flanges for this conversion.
Side Supply and Return Units (50A4,A5,A8,A9) with Field-
Installed Power Exhaust in Return Duct
Space must be available in the return duct to mount the power ex
-
haust fan (gravity relief) modules. Dimensions and suggested lo
-
cations are shown in Fig. 43. These instructions are a guideline
and not a comprehensive procedure. The design contractor must
provide some design initiative.
The wiring harness that is provided with the power exhaust acces
-
sory is not long enough for the fan modules to be mounted in the
return air duct. Field-supplied wiring must be spliced into the har
-
ness. Use a junction box at each splice. The wiring may be run in
the return duct as shown in Fig. 43 or externally in conduit. A ser
-
vice access panel will be needed near each power exhaust fan.
BACnet
1
Communication Option Wiring
WIRING THE UPC OPEN CONTROLLER TO THE MS/TP
NETWORK
The UPC Open controller communicates using BACnet on an
MS/TP network segment communications at 9600 bps, 19.2 kbps,
38.4 kbps, or 76.8 kbps.
Wire the controllers on an MS/TP network segment in a daisy-
chain configuration. Wire specifications for the cable are 22 AWG
(American Wire Gage) or 24 AWG, low-capacitance, twisted,
stranded, shielded copper wire. The maximum length is 2000 ft.
Install a BT485 terminator on the first and last controller on a net
-
work segment to add bias and prevent signal distortions due to
To wire the UPC Open controller to the BAS network:
1. Pull the screw terminal connector from the controller’s BAS
Port.
2. Check the communications wiring for shorts and grounds.
3. Connect the communications wiring to the BAS port’s screw
terminals labeled Net +, Net -, and Shield.
NOTE: Use the same polarity throughout the network segment.
4. Insert the power screw terminal connector into the UPC
Open controller’s power terminals if they are not currently
connected.
5. Verify communication with the network by viewing a module
status report. Perform a Modstat using the i-Vu tools Field
Assistant.
To install a BT485 terminator, push the BT485 terminator on to
the BT485 connector located near the BACnet connector.
NOTE: The BT485 terminator has no polarity associated with it.
To order a BT485 terminator, consult Commercial Products i-Vu
®
Open Control System Master Prices.
MS/TP WIRING RECOMMENDATIONS
Recommendations are shown in Tables 9 and 10. The wire jacket
and UL temperature rating specifications list two acceptable alter
-
natives. The Halar
2
specification has a higher temperature rating
and a tougher outer jacket than the SmokeGard
3
specification, and
it is appropriate for use in applications where the user is concerned
about abrasion. The Halar jacket is also less likely to crack in ex
-
tremely low temperatures.
NOTE: Use the specified type of wire and cable for maximum sig
-
nal integrity.
IMPORTANT: The following section is a guideline and not a
comprehensive procedure to field modify the units. The
installing contractor must provide some design initiative. Field
conversion is complex and is not recommended. Units with
electric heat must not be converted because of potential heat
-
ing mode operating problems.
1. BACnet is a trademark of ASHRAE.
2. Halar is a registered trademark of Solvay Plastics.
3. SmokeGard is a trademark of AlphaGary-Mexichem Corp.