Trane IntelliPak WEHE Series Installation, Operation And Maintenance Manual page 10

General Information
Ventilation Control Module (VCM - Design
special option only)
The Ventilation Control Module (VCM) is located in the
filter section of the unit and is linked to the unit's UCM
network. Using a "velocity pressure" sensing ring located
in the fresh air section, allows the VCM to monitor and
control the quantity of fresh air entering the unit to a
minimum airflow setpoint.
An optional temperature sensor can be connected to the
VCM which enables it to control a field installed fresh air
preheater.
An optional CO sensor can be connected to the VCM to
2
control CO reset. The reset function adjust the minimum
2
cfm upward as the CO concentrations increase. The
2
maximum effective (reset) setpoint value for fresh air
entering the unit is limited to the systems operating cfm.
Table 3 lists the Minimum Outside Air cfm vs Input
Voltage.
Table 3. Minimum outside air cfm vs input voltage
Minimum Outside Air Setpoint w/VCM Module & Traq™
Sensing
Casing Input Volts
2 0.5 - 4.5 vdc
3 0.5 - 4.5 vdc
4 0.5 - 4.5 vdc
5 0.5 - 4.5 vdc
6 0.5 - 4.5 vdc
9 0.5 - 4.5 vdc
Note: Refer to the "Traq™ Sensor Sequence of Operation"
section for VCM operation.
Velocity Pressure Transducer/Solenoid
Assembly Generic Building Automation
System Module (GBAS - Optional 1U51 used
with non-Trane building control systems)
The Generic Building Automation System (GBAS) module
allows a non-Trane building control system to
communicate with the rooftop unit and accepts external
setpoints in form of analog inputs for cooling, heating,
supply air pressure, and a binary input for demand limit.
Refer to the "Field Installed Control Wiring" section
for the input wiring to the GBAS module
and the various desired setpoints
corresponding DC voltage inputs for both VAV and CV
applications.
For complete application details of the module, refer to
Engineering Bulletin UN-PRB001-EN.
Input Devices & System Functions
The descriptions of the following basic Input Devices used
within the UCM network are to acquaint the operator with
their function as they interface with the various modules.
10
CFM
0 - 14000
0 - 17000
0 - 22000
0 - 28000
0 - 33000
0 - 46000
(p. 49),
(Figure 36, p. 61)
(Table 16, p. 61) with the
Refer to the unit's electrical schematic for the specific
module connections.
Constant Volume & Variable Air Volume Units
Supply Air Temperature Sensor (3RT9)
Is an analog input device used with CV & VAV applications.
It monitors the supply air temperature for; supply air
temperature control (VAV), supply air temperature reset
(VAV), supply air temperature low limiting (CV), supply air
tempering (CV/VAV). It is mounted in the supply air
discharge section of the unit and is connected to the RTM
(1U48).
Return Air Temperature Sensor (3RT6)
Is an analog input device used with a return humidity
sensor on CV & VAV applications when the comparative
enthalpy option is ordered. It monitors the return air
temperature and compares it to the outdoor temperature
to establish which temperature is best suited to maintain
the cooling requirements. It is mounted in the return air
section and is connected to the ECEM (1U52).
Entering Evaporator Temperature Sensor
(3RT28 and 3RT29)
This analog input device is used with the Leaving
Evaporator Temp sensor to provide Low Charge Protection
of the refrigerant systems. The difference in these two
temperatures will be monitored during compressor
operation and compressor circuits will be shut down if this
difference exceeds a Human Interface selectable setpoint
value.
Leaving Evaporator Temperature Sensor
(3RT14 and 3RT15)
An analog input device used with CV and VAV applications
that monitors the refrigerant temperature inside the
evaporator coil to prevent coil freezing. It is attached to the
suction line near the evaporator coil and is connected to
the MCM. It is factory set for 30°F and has an adjustable
range of 25°F to 35°F. The compressors are staged "Off" as
necessary to prevent icing. After the last compressor stage
has been turned "Off", the compressors will be allowed to
restart once the evaporator temperature rises 10°F above
the "coil frost cutout temperature" and the minimum three
minute "Off" time has elapsed.
Filter Switch (3S21)
Is a binary input device used on CV & VAV applications. It
measures the pressure differential across the unit filters. It
is mounted in the filter section and is connected to the RTM
(1U48). A diagnostic SERVICE signal is sent to the remote
panel if the pressure differential across the filters is at least
0.5" w.c. The contacts will automatically open when the
pressure differential across the filters decrease to 0.4" w.c.
The switch differential can be field adjusted between 0.17"
w.c. to 5.0" w.c. ± 0.05" w.c.
RT-SVX35H-EN