Trane RT-PRC010-EN Manual page 82

near the TXV bulb location to shut the
cooling off when coil frosting conditions
occur. The supply fans are not shut off
and will de-ice the coil. Timers prevent
the compressors from rapid cycling.
7
Occupied/Unoccupied Switching
a
Description — 3 ways to switch
Occupied/Unoccupied:
(1) NSB Panel
(2) Field-supplied contact closure
(hardwired binary input to RTM)
(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 rooftop.
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 depending on
set-up parameters. As the building load
changes, the night setback sensor
energizes 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
Unoccupied output relay contacts on the
Rooftop Module (RTM) or by using
changeover thermostats. Either of these
methods will assure adequate airflow
through the unit and satisfactory
temperature control of the building.
82
Controls
Occupied/Unoccupied input on the RTM
This input accepts a field supplied switch
or contacts closure such as a time clock.
Trane Tracer® System
The Trane Tracer System can control the
Occupied/Unoccupied status of
the rooftop.
8
Timed Override Activation — ICS
This function is operational when the
RTM is the zone temperature sensor
source, which was set up at the Human
Interface Panel. When this function is
initiated by the push of a override button
on the ICS sensor, the 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-ICS
This function is active whenever the
RTM is selected as the Zone Temperature
Sensor source, which was set up at the
Human Interface Panel. When this
function is initiated by the push of an
override button on the zone sensor, the
unit will switch to the Occupied mode.
Automatic Cancellation of the Timed
Override Mode occurs after three hours
of operation.
9
Low Ambient Compressor Lockout
This function will lock out the
compressor if the outdoor air
temperature is below the low ambient
compressor lock out temperature set
point. The factory setpoint is 50 F on
standard units and 0 F on low ambient
units. This setpoint is adjustable at the
Human Interface Panel. Compressors
will be locked out when outdoor air
temperatures falls below that selected
temperature and will be allowed to start
again when the temperature rises 5 F
above the setpoint.
10
Comparative Enthalpy Control of
Economizer
An optional Comparative Enthalpy
system is used to control the operation
of the economizer, and measures the
temperature and humidity of both return
(VAV/CV Units)
air and outside air to determine which
source has lower enthalpy. This system
allows true comparison of outdoor air
and return air enthalpy by measurement
of outdoor air and return air
temperatures and humidities.
Reference Enthalpy Control of
Economizer
The optional reference enthalpy
compares ambient temperature and
humidity to the economizer enthalpy
control setpoint. If ambient temperature
and humidity are below the economizer
enthalpy control setpoint the economizer
will operate freely. This system provides
more sophisticated control where
outdoor air humidity levels may not be
acceptable for building comfort and
indoor air quality.
Dry Bulb Temperature Control of
Economizer
The optional dry bulb system measures
ambient temperature comparing it to the
economizer control temperature
setpoint. If the ambient temperature is
below the economizer dry bulb
temperature control setpoint, the
economizer will operate freely. This
system is best suited for arid regions
where the humidity levels of fresh air
would not be detrimental to building
comfort and indoor air quality.
11
Compressor Lead/Lag
Compressor lead/lag is a user-selectable
feature through the Human Interface
Panel available on all units. After each
request for compressor operation, the
lead refrigeration circuit or compressor
on 20-30 tons units switches, thereby
causing a more equitable or balanced
run time among compressors.
12
Emergency Stop Input
A binary input is provided on the
Rooftop Module (RTM) for installation
of field provided switch or contacts for
immediate shutdown of all unit
functions.
RT -PRC010-EN