Ingersoll-Rand ReliaTel, Manual, Page: 71 / 176

RT-SVD03L-EN 71
then be modulated to maintain the discharge air
temperature to the DACSP.
For Voyager ™ light commercial units, if there is
additional demand for cooling once the VSPD
compressor has reached its maximum speed for Stage
1, the controller will energize the first fixed speed
compressor on circuit 2. Once the first fixed speed
compressor is energized, the VSPD compressor speed
will be reduced to its minimum speed for Stage 2 of
compressor operation and then will be released back to
discharge air temperature control. This process will be
repeated for the transition between Stages 2 and 3.
Once the active cooling demand has been satisfied for
Voyager
™ light commercial units, compressors will
begin staging down in reverse order from the stage up
sequence. Once the VSPD compressor has reached its
minimum speed for any given stage of cooling, if the
cooling demand continues to decrease, the last fixed
speed compressor to energize will be de-energized.
Once a fixed speed compressor is de-energized, the
VSPD compressor will be increased to its maximum
value for the active stage of compressor operation and
will then be released back to normal control. After the
unit has staged down all fixed compressors, then only
the VSPD compressor will be left operating and the
following information applies to both Voyager
™ light
commercial and Precedent ™ units: Once there is no
longer a demand for the VSPD compressor, the VSPD
compressor will modulate down to its minimum speed
and then will be de-energized, while adhering to all
shutdown requirements. Once all compressors have
de-energized, the economizer, if enabled, will be
allowed to close back to minimum position if there is
no longer a demand.
N No otte e:: In all cases, during normal compressor operation,
the VSPD compressor will be subject to a 3-
minute minimum ON/OFF time and the supply
fan will continue to be controlled by the supply
air pressure.
Unoccupied DX & Economizer Cooling
Control
For unoccupied DX and economizer cooling control,
the unit will operate as a standard fixed-speed
compressor unit1. During all requests for cooling
operation during unoccupied mode, the unit will
operate the VSPD compressor at 100% of the available
capacity 2. When compressor operation is requested,
the VSPD compressor will be started first and its speed
will be increased up to 100%, based on the unit
configuration. If in the case of the multi-compressor
unit, the VSPD compressor alone cannot meet the
space demand; the unit will begin to stage up
additional compressors to meet the demand.
N No otte e:: Light commercial units do not support
unoccupied mode without a BAS system or
programmable zone sensor to support the
needed unoccupied heat/cool setpoints.
Demand limits, restricting available compressor
capacity, are to have higher priority over the
commanded compressor capacity staging level
due to occupancy status.
Dehumidification is not currently supported on multi-
zone VAV.
Single Zone VAV Cooling - Supply Fan
Output Signal Control
No new supply fan technology is required to support
the VSPD compressor application - existing supply fan
types will be utilized. While no new fan technology is
required, a change will be required to optimize the unit
control with a VSPD compressor. Modifications will be
made to the minimum fan speed based on active
compressor capacity.
Discharge Air Temperature
Control
Occupied DX & Economizer Cooling
Control
For normal cooling operation, the total cooling capacity
will be modulated and staged in order to meet the
calculated DACSP, as standard fixed speed compressor
units.
Unoccupied DX & Economizer Cooling
Control
For unoccupied DX and economizer cooling control,
the unit will operate as during normal occupied mode -
compressor capacity will be varied to maintain the
discharge air temperature requirements and the supply
fan will remain in control based on the active
compressor capacity and space demand.
Enhanced Dehumidification
Enhanced dehumidification on ReliaTel ™ SZVAV VSPD
compressor units will use a slower minimum indoor
fan speed at a constant compressor stage to achieve
dehumidification.
Active Cooling Mode Operation
When the unit is in active cooling mode, the unit is
allowed to enter enhanced dehumidification if space
humidity > dehumidification setpoint and the zone
temperature conditions are satisfied.
When the unit enters enhanced dehumidification, the
compressor staging will be held at current conditions
and fan will drop to the minimum speed operating
range. Enhanced dehumidification will continue to run
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