12
RSMV Technical Guide
SEQUENCE OF OPERATIONS
Cooling Mode and Dehumidification Operation
Cooling Mode Operation
In the Cooling Mode, as the Supply Air Temperature (SAT) rises
above the Active SAT Cooling Setpoint, the compressors will stage
on and modulate to maintain the Active Evaporator Coil Suction
(Saturated) Temperature Setpoint. One set of tandem compressors
(a VFD compressor and a fixed stage compressor) are controlled
per RSMV. Multiple RSMVs are needed for multiple sets of tandem
compressors.
In units with one set of tandem compressors, if the VFD compressor
modulates to 100% and the SAT is still above the SAT Cooling
Setpoint for the Cooling Stage Up Delay, then the fixed compressor
will stage on. The VFD compressor will then be allowed to modulate
as necessary to maintain the Active Evaporator Coil Suction
(Saturated) Temperature Setpoint. Minimum off times must also be
met before compressors can stage on.
Stage Down Compressors
If the VFD compressor(s) have modulated down to 30% for the Stage
Down Delay period and the SAT has fallen below the SAT Cooling
Setpoint minus the Stage Control Window, then the last compressor
to have staged on (VFD or Fixed) will stage off – assuming its
Minimum Run Time has been met. Any remaining VFD compressors
are then allowed to modulate as needed. If the last remaining VFD
compressor reaches 0% for the Stage Down Delay, it will stage off.
Dehumidification Operation
Once in Dehumidification Mode, units with fixed compressors
will activate the compressors to maintain the Evaporator Coil
Suction (Saturated) Temperature Setpoint. An RSMV Module will
be required for each fixed compressor or each fixed compressor
tandem pair in order to monitor the suction (saturated) temperature
and control the compressor(s) accordingly. Each RSMV will
independently activate and stage its compressor(s) to maintain that
circuit’s Suction (Saturated) Temperature Setpoint. The staging of
compressors on an RSMV is subject to Stage Up and Stage Down
Delays as well as compressor Minimum Run Times and Minimum
Off Times.
A suction pressure transducer is used and the VCCX2 Controller
converts that to a Suction (Saturated) Temperature value.
On units with one or more sets of VFD/Fixed tandem compressors,
each set of tandem compressors (one circuit) will be controlled by
a separate RSMV Module with its own Suction Pressure Transducer
(converted to a Suction (Saturated) Temperature). Once the unit
enters the Dehumidification Mode, each RSMV will initially
activate the VFD compressor as required to maintain the Suction
(Saturated) Temperature Setpoint. At that point, each RSMV will
modulate its VFD compressor and enable the fixed compressor, as
necessary, to maintain the Suction (Saturated) Temperature Setpoint
for that circuit.
If the VFD compressor reaches 100% for the Stage Up Delay and
the Suction (Saturated) Temperature is still above setpoint, then the
fixed compressor will stage on while the VFD compressor modulates
as needed. If the VFD compressor has modulated down to 0%
and the Suction (Saturated) Temperature is 5ºF below the Suction
(Saturated) Temperature for the Stage Down Delay period, the fixed
compressor will stage off and the VFD compressor will continue to
modulate. During this operation, compressor Minimum Run Times
and Minimum Off Times must be met.
NOTE:
If the Coil Temperature drops below 32˚F, any
cooling remaining on will be forced to stage off.
Summary of Contents for RSMV ASM01686
Page 1: ...RSMV Technical Guide ...
Page 31: ...31 RSMV Technical Guide NOTES ...
