11 2 RT-SVX34C-EN
Sequence of Operation
Mechanical Cooling Sequence Of Operation
Time delays are built into the controls to increase reliability and performance by protecting the
compressors and maximizing unit efficiency.
Dehumidification (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 dehumidification.
A Voyager Commercial Rooftop unit can contain one or two refrigerant circuits. Units with
dehumidification 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 dehumidification 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
dehumidification mode.
During dehumidification 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
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 dehumidification mode, to ensure proper oil distribution throughout the reheat
and cooling condenser circuits, a purge is initiated by a hardcoded 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 Dehumidification Low Pressure Control section for the reheat low pressure control (RLP)
function during active dehumidification.
See Dehumidification 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 dehumidification control. For both multi-circuit and
single circuit units, any sensible heating request will terminate dehumidification control. If heating
is active at the time a call for dehumidification control is received the heating operation must
complete and an additional 5 minutes from the time heat is terminated must elapse before
dehumidification will be allowed.
Note: 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
dehumidification control.
Note: Occupied CV and all unoccupied operation will terminate dehumidification if the sensible
zone cooling requirements exceeds one-half the available cooling capacity of the unit.
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