RT-PRC007-EN
60
Controls
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 Economizer Actuator 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 RTRM
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).
