Modulating Hot Gas Reheat Sequence Of; Operation; Sensible Cooling Or Heating Control; Overrides Hot Gas Reheat - Trane Voyager Commercial Installation, Operation And Maintenance Manual

S S e e q q u u e e n n c c e e o o f f O O p p e e r r a a t t i i o o n n
overrides the DCV CO reset calculation of Min OA
2
Flow Target as well.
The measured OA CFM value from the local sensor
input will normally be used for this function. At this
time OA CFM value from other sources is not
supported.
The algorithm used for this function will be P+I, with
integration occurring only when outside the deadband.
As long as the measured airflow is within the
deadband, the control will be satisfied. When the OA
CFM value is above the upper deadband limit the
algorithm will decrease the Traq OA Min Damper
Position Request allowing less fresh air into the space.
When the OA CFM value is below the lower deadband
limit the algorithm will increase the Traq OA Damper
Min Position Request allowing more fresh air into the
space. The OA CFM Deadband will be hard coded to +/-
250 CFM.
Traq with Demand Controlled Ventilation
(DCV)
If Demand Controlled Ventilation is enabled, the
Minimum OA CFM control point will be modified by
high CO concentrations resetting the setpoint
2
between Design and DCV Minimum OA CFM setpoint
limits. The Traq airflow control functionality described
above will then use the calculated Min OA Flow Target
for determining the Traq OA Minimum Position
Request.
Modulating Hot Gas Reheat
Sequence of Operation
When the relative humidity in the controlled space (as
measured by the sensor assigned to space humidity
sensing) rises above the space humidity setpoint,
compressors and the supply fan will energize to reduce
the humidity in the space. All compressors on both
refrigerant circuits will be staged up during active hot
gas reheat.
A Voyager Commercial Rooftop unit can contain one or
two refrigerant circuits. Units with hot gas reheat will
have one circuit with an outdoor condenser coil located
in the outdoor section for normal head pressure control
and a reheat coil located in the indoor air stream
section for supply air reheat; both coils are for the
same circuit. For 40-50 ton Voyager Commercial units
the reheat circuit is circuit# 2. For 27.5-35 ton Voyager
Commercial units there is only one circuit.
During hot gas reheat mode, the CLV and RHP will
modulate which will allow refrigerant to flow through
both the condenser coil and the reheat coil. The RHP
will be de-energized when in hot gas reheat mode.
During hot gas reheat mode, the Supply Air
Temperature is controlled to the Supply Air Reheat
Setpoint by controlling the reheat and cooling
modulating valve position. The range for the Supply
110
Air Reheat Setpoint is 65°F to 80°F and the default is
70°F. The Supply Air Reheat Setpoint is adjusted by
using a potentiometer on the RTOM.
During cooling operation, the cooling valve (CLV) will
be open 100% and the reheat valve (RHV) will be closed
which will allow refrigerant to flow through the
condenser coil and not the reheat coil. During cooling
mode the reheat pump-out solenoid (RHP) will also be
energized to allow refrigerant to be removed from the
reheat coil.
During cooling or hot gas reheat mode, to ensure
proper oil distribution throughout the reheat and
cooling condenser circuits, a purge is initiated by a
hard coded purge interval timer. After the purge
interval timer reaches 60 minutes, the unit performs a
purge for a fixed 3-minute time period. During this
state the reheat and cooling valve will be driven 50%
and the reheat pump-out solenoid is energized.
See Hot Gas Reheat Low Pressure Control section for
the reheat low pressure control (RLP) function during
active dehumidification.
See Hot Gas Reheat Frost Protection section for the
control scheme during active dehumidification.
See the Condenser Fan / Compressor sequence section
for Condenser fan staging during active
dehumidification.

Sensible Cooling or Heating Control

Overrides Hot Gas Reheat Control
For both multi-circuit and single circuit units, any
sensible heating request will terminate hot gas reheat
control. If heating is active at the time a call for hot gas
reheat control is received the heating operation must
complete and an additional 5 minutes from the time
heat is terminated must elapse before hot gas reheat
will be allowed.
N N o o t t e e : : Occupied VAV operation in cooling mode will
consider a critical zone temperature and when
the sensible cooling requirements of this zone
are not being met, the unit will terminate hot gas
reheat control.
N N o o t t e e : : Occupied CV and all unoccupied operation will
terminate hot gas reheat if the sensible zone
cooling requirements exceeds one-half the
available cooling capacity of the unit.

Gas Heat Sequence Of Operation

When heating is required, the RTRM initiates the
heating cycle through the ignition control module
(IGN). The IGN normally open contacts close to start
the combustion blower motor (CBM) on high speed.
Next, the IGN control energizes the hot surface igniter
(IP) for 45 seconds. After a preheat period, the gas
valve (GV) is energized for approximately 7 seconds. If
the burner lights, the gas valve remains energized. If
the burner fails to ignite, the ignition module will
RT-SVX34R-EN