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relay is energized when enthalpy is high (above 28 BTU/lb OR
dry bulb temperature is above 75°F) and de-energized when en-
thalpy is low (below 27 BTU/lb AND dry bulb temperature is be-
low 74.5°F). The enthalpy input is dedicated to input 8 and tells
the VAV-RTU Open when the outside air enthalpy is HIGH or
LOW. The normal condition for the enthalpy input is HIGH. En-
thalpy is configured on input 8 in the factory when it is added as
an option.
NOTE: The enthalpy calculation is done using an average altitude
of 1000 ft above sea level.
For field installation, refer to the enthalpy accessory instructions.
For wiring see Fig. 2 and Fig. 5-10. The VAV-RTU Open board
provides 24vac on one of the two loose grey wires in the return air
section of the rooftop near the 12-pin economizer plug. To deter-
mine the correct grey, measure the voltage on the wires with pow-
er applied to the unit. If 24-vac is sensed, then that is the grey wire
that is connected to the VAV-RTU Open board at J2-7. The other is
the signal for input 8, connect it to the LOW Enthalpy terminal on
the enthalpy switch/receiver. Tie into the 12-pin economizer plug
on pin 4 or the black wire connected to the actuator for the enthal-
py's GND connection. Power can also be provided direct from the
unit transformer and J5 terminal on the VAV-RTU Open.
•
J2-7 or J5-2 = 24 VAC for enthalpy switch power
•
J2-6 or J5-1 = input signal
DIFFERENTIAL ENTHALPY
Differential enthalpy control requires both an enthalpy switch/re-
ceiver (33CSENTHSW) and an enthalpy sensor (33CSENTSEN).
The enthalpy sensor must be installed in the field as the factory can
only provide single enthalpy. The enthalpy sensor must be mounted
in the return airstream and calculates the enthalpy of the indoor air.
The relay is energized when the enthalpy detected by the return air
enthalpy sensor is less than the enthalpy at the enthalpy switch/re-
ceiver. The relay is de-energized when the enthalpy detected by the
return air enthalpy sensor is greater than the enthalpy at the enthalpy
switch/receiver (differential enthalpy control).
To wire return air enthalpy sensor:-MP
Connect the 4-20 mA In terminal on the enthalpy switch/ receiver
to the 4-20 mA Out terminal on the return air enthalpy sensor.
Connect the 24-36 VDC Out terminal on the enthalpy switch/re-
ceiver to the 24-36 VDC In terminal on the return air enthalpy sen-
sor. (See Fig. 14.)
J2-7 or 24vac (R)
GND (C)
J2-6
GRY
HI
LOW
GND 24
4-20
24-36
ENTHALPY
VAC
mA
VDC
IN
OUT
33CSENTHSW
Fig. 14 — Enthalpy Switch and Sensor Wiring
FIRE SHUTDOWN
The fire shutdown input is provided for unit shutdown in response
to a fire alarm or smoke detector. The fire shutdown input is dedi-
cated to input 5 and tells the VAV-RTU Open when to shutdown
due to smoke detection or fire alarm system. The normal condition
for fire shutdown is there is no fire alarm. The unit may have fac-
tory installed smoke detector(s); refer to the base unit installation
instructions for details on any adjustments required during unit in-
stallation. Fire shutdown is always factory configured for a nor-
mally open smoke detector.
For field installation of a smoke detector see instructions for that
specific accessory. See below and the troubleshooting section for
wiring at the unit's Integrated Staging Control (ISC) board.
•
•
NOTE: Input 5 can also be wired into J5-3.
FILTER STATUS
The filter status accessory is a field-installed accessory. This ac-
cessory detects plugged air filters. When installing this accessory,
the unit must have a free input (input 3, 5, 8, or 9). One of the ded-
icated functions (Fire shutdown, Enthalpy, or Compressor safety)
must not be in use to configure Filter Status. Refer to the configu-
ration section for details on configuring inputs for specific func-
tions and state. Refer to Fig. 2 for wire terminations at J5.
FAN STATUS
The fan status accessory is a field-installed accessory. This acces-
sory detects when the indoor fan is moving air. When installing
this accessory, the unit must have a free input (input 3, 5, 8, or 9).
One of the dedicated functions (Fire shutdown or Enthalpy) must
not be in use to configure Fan Status. Refer to the configuration
section for details on configuring inputs for specific functions and
state. Refer to Fig. 2 for wire terminations at J5.
IGC OVERRIDE
The IGC Override input is factory-installed for 48LC gas heat
units. This input provides an indication that the gas valve is stuck
open and the heat is still operating after any call for heating has
been dropped. This function requires the use of input 9. Any of the
other dedicated functions (Fan Status, Filter Status, Remote Occu-
pancy, or Door Contact) will not be in use if IGC Override is con-
figured. Refer to the configuration section for details on configur-
ing inputs for specific functions and state. Refer to Fig. 5 for wire
terminations.
Communication Wiring
GENERAL
Protocols are the communication languages spoken by control de-
vices. The main purpose of a protocol is to communicate informa-
tion in the most efficient method possible. Different protocols ex-
ist to provide different kinds of information for different applica-
tions. In the BAS application, many different protocols are used,
depending on manufacturer. Protocols do not change the function
of a controller; just make the front end user different.
The VAV-RTU Open is set to communicate on BACnet MS/TP.
Switch 3 (SW3) on the board is used to set protocol and baud rate.
Switches 1 and 2 (SW1 and SW2) are used to set the board's net-
work address. See Fig. 15 and 16 for protocol switch settings and
24-36
4-20
address switches. For network wiring reference refer to MS/TP
VDC
mA
IN
OUT
Networking and Wiring Installation Guide.
NOTE: Power must be cycled after changing the SW1-3 switch
settings.
33CSENTSEN
BACNET MS/TP
BACnet Master Slave/Token Passing (MS/TP) is used for com-
municating BACnet over a sub-network of BACnet-only control-
lers. This is the default Carrier communications protocol. Each
VAV-RTU Open module acts as an MS/TP Master. The speed of
an MS/TP network can range from 9600 to 76.8K baud. Physical
Addresses can be set from 01 to 99.
Wiring BACnet MS/TP network for VAV System
The VAV Open Control System uses linkage to exchange data be-
tween the zone terminals and their air source to form a coordinated
HVAC system. The system's air source controller and zone con-
trollers are linked so that their data exchange can be managed by
one zone controller configured as the VAV Master (see Fig. 17 and
18).
15
ISC - UNIT SHUTDOWN - 24v OUT = 24 VAC source
ISC - UNIT SHUTDOWN - Smoke Alarm = Signal input
to VAV-RTU Open
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