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 connections may be field-modified to accommodate side re-
turn air connections.
Conversion to horizontal return requires that the bottom re-
turn openings of the unit must be sealed with airtight panels ca-
pable of supporting the weight of a person. The return ductwork
connection locations on the side of the unit are higher than nor-
mal (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 barometric 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
panels capable of supporting the weight of a person.
2. Remove the panels located below the economizer out-
door-air dampers. These openings will be used for the re-
turn-air ductwork. There are 2 panels on
50A3,A6,A7020-050 units. There are 3 panels on
50A2,A3,A6,A7060 units. These openings are normally
used for power exhaust or barometric relief.
3. Run the return air ductwork up to the openings. One sin-
gle duct is recommended to connect to the unit over the
return air openings. See Fig. 43. The return duct must in-
corporate 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 exhaust fan
(gravity relief) modules. Dimensions and suggested locations
are shown in Fig. 43. These instructions are a guideline and not
a comprehensive procedure. The design contractor must pro-
vide some design initiative.
The wiring harness that is provided with the power exhaust
accessory is not long enough for the fan modules to be mount-
ed in the return air duct. Field-supplied wiring must be spliced
into the harness. 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 service 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-capaci-
tance, twisted, stranded, shielded copper wire. The maximum
length is 2000 ft.
Install a BT485 terminator on the first and last controller on
a network segment to add bias and prevent signal distortions
due to echoing. See Fig. 44-46.
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 seg-
ment.
4. Insert the power screw terminal connector into the UPC
Open controller’s power terminals if they are not current-
ly connected.
5. Verify communication with the network by viewing a
module status report. To perform a module status report
using the BACview
2
keypad/display unit, press and hold
the “FN” key then press the “.” key.
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 — Recommen-
dations are shown in Tables 9 and 10. The wire jacket and UL
temperature rating specifications list two acceptable alterna-
tives. The Halar
3
specification has a higher temperature rating
and a tougher outer jacket than the SmokeGard
4
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 extremely low temperatures.
NOTE: Use the specified type of wire and cable for maximum
signal 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 heating mode operating problems.
1. BACnet is a registered trademark of ASHRAE (American Society
of Heating, Refrigerating, and Air-Conditioning Engineers).
2. BACview is a registered trademark of Automated Logic Corporation.
3. Halar is a registered trademark of Solvay Plastics.
4. SmokeGard is a trademark of AlphaGary-Mexichem Corp.
