AAON RSMV-HP, Technical Manual, Page: 10 / 32

Zone
Zone
SEQUENCE OF OPERATIONS
RSMV-HP Technical Guide
10
Cooling Mode
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 fi xed stage compressor) are controlled per
Refrigerant System Module-VFD Compressor (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 fi xed 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.
To 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 .
Dehumidi fi cation Operation
Once in Dehumidifi cation Mode, units with fi xed 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 VCC-X / 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 Dehumidifi cation 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 fi xed 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
fi xed 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 5 degrees below the Suction
(Saturated) Temperature for the Stage Down Delay period, the fi xed
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.
SAFETY: If the Coil Temperature drops below 32˚F, any
cooling remaining on will be forced to stage off .
Electronic Expansion Valve (EXV)
Operation
If EXV’s are being used, a Coil (Suction Line) Temperature Sensor
will measure the Coil (Suction Line) Temperature after each
Evaporator Coil line for each compressor, and this sensor will be
connected to an RSMV-HP Module. This temperature will be used
in conjunction with the calculated saturated refrigerant temperature
to calculate the Superheat of each evaporator coil. The EXV for
each coil will then be controlled to maintain the Superheat Setpoint.
Head Pressure Control
The Refrigeration System Module for VFD Heat-Pump Compressors
(RSMV-HP) can monitor a Head Pressure Transducer and control a
Condenser Fan to maintain a Head Pressure Setpoint. The RSMV-HP
must be confi gured for an Air Cooled Condenser.
A Condenser Relay is commanded on when the fi rst compressor is
enabled (except if the unit is in Heat Pump Defrost Mode). On an
Air Cooled Unit, the Condenser Fan will be controlled with 0-10
VDC output signal or a PWM output signal. Both outputs operate
simultaneously.
When the Condenser Signal fi rst activates, it maintains at 100% for
10 seconds.
In the Cooling Mode, the Condenser Signal will modulate to maintain
the Cooling Head Pressure Setpoint. The signal can modulate
between 15% and 100%. If the Head Pressure exceeds 550 PSIG,
the condenser control signal will immediately go to 100% and a High
Head Pressure Alarm will be generated. The alarm will be deactivated
when the Head Pressure drops below 540 PSIG.
In the Dehumidifi cation Mode, the Condenser Output Signal controls
to the Reheat Head Pressure Setpoint. High Head Pressure conditions
produce the same eff ects as in the Cooling Mode.
If no Head Pressure Sensor is detected, the Condenser the Condenser
Output Signal will be maintained at 100%.
Cooling Mode, EXV Operation & Head Pressure Control