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31RT-PRC007-EN
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Coil Freeze Protection FROSTAT™
The FROSTAT system eliminates the
need for hot gas bypass and adds a
suction line surface temperature sensor
to determine if the coil is in a condition
of impending frost. If impending frost is
detected primary cooling capacity is
shed as necessary to prevent icing. All
compressors are turned off after they
have met their minimum 3 minute on
times. The supply fan is forced on until
the FROSTAT device no longer senses a
frosting condition or for 60 seconds after
the last compressor is shut off,
whichever is longer.
Occupied/Unoccupied Switching
There are 3 ways to switch Occupied/
Unoccupied:
1
NSB Panel
2
Electronic time clock or field-supplied
contact closure
3
TRACER
Night Setback Sensors
Trane’s night setback sensors are
programmable with a time clock function
that provides communication to the
rooftop unit through a 2-wire
communications link. The desired
transition times are programmed at
the night setback sensor and
communicated to the unit.
Night setback (unoccupied mode) is
operated through the time clock
provided in the sensors with night
setback. When the time clock switches to
night setback operation, the outdoor air
dampers close and heating/cooling can
be enabled or disabled. As the building
load changes, the night setback sensor
communicates the need for the rooftop
heating/cooling (if enabled) function and
the evaporator fan. The rooftop unit will
cycle through the evening as heating/
cooling (if enabled) is required in the
space. When the time clock switches
from night setback to occupied mode, all
heating/cooling functions begin normal
operation.
When using the night setback options
with a VAV heating/cooling rooftop,
airflow must be maintained through the
rooftop unit. This can be accomplished
by electrically tying the VAV boxes to the
VAV heat relay contacts on the Low
voltage terminal board or by using
changeover thermostats. Either of these
methods will assure adequate airflow
through the unit and satisfactory
temperature control of the building.
Timed override Activation—ICS
When this function is initiated by
pushing the override button on the ICS
sensor, TRACER will switch the unit to
the occupied mode. Unit operation
(occupied mode) during timed override
is terminated by a signal from TRACER.
Timed override Activation—Non-lCS
When this function is initiated by the
push of an override button on the
programmable zone sensor, the unit will
switch to the occupied mode. Automatic
Cancellation of the Timed override Mode
occurs after three hours of operation.
Comparative Enthalpy Control of
Economizer
The Unitary Economizer Module (UEM)
receives inputs from optional return air
humidity and temperature sensors and
determines whether or not it is feasible
to economize. If the outdoor air enthalpy
is greater than the return air enthalpy
then it is not feasible to economize and
the economizer damper will not open
past its minimum position.
Fan Failure Switch
The fan failure switch will disable all unit
functions and “flash” the Service LED on
the zone sensor.
Emergency Stop Input
A binary input is provided on the UCP for
installation of field provided switch or
contacts for immediate shutdown of all
unit functions. The binary input is
brought out to Low Voltage Terminal
Board One (LTB1).