AAON RSMD, Техническое руководство

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12
RSMD Technical Guide
SEQUENCE OF OPERATIONS
Cooling Mode, Dehumidification, and Head Pressure Control
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. Two compressors are
controlled per Refrigerant System Module ( RSMD). Multiple
RSMDs are needed when there are more than two compressors.
In units with one digital and one fixed compressors, if the digital
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 digital 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.
In units with multiple digital compressors, if the 1st digital
compressor modulates to 100% and the SAT is still above the SAT
Cooling Setpoint for the Cooling Stage Up Delay, then the 2nd
digital compressors will enable and the two digital Compressors
will then modulate together to maintain the Active Evaporator
Coil Suction (Saturated) Temperature Setpoint.
To stage down compressors, if the digital 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 (digital or Fixed) will stage off – assuming its Minimum
Run Time has been met. Any remaining digital compressors
are then allowed to modulate as needed. If the last remaining
digital compressor reaches 0% for the Stage Down Delay, it
will stage off.
Dehumidification Operation
The RSMD activates the Cooling Stages based on the actual
Evaporator Coil Temperature compared to the Evaporator Coil
Suction (Saturation) Temperature Setpoint. The Evaporator
Coil Suction (Saturation) Temperature is calculated by using
the Suction Pressure Sensor and converting the pressure to
temperature.
For Copeland Digital Scroll™ Compressor units, the RSMD will
modulate the Copeland Digital Scroll™ Compressor to maintain
the Evaporator Coil Suction (Saturation) Temperature Setpoint
and activate the Compressors as necessary.
On units that have one Digital and one Fixed Capacity
Compressor, if the Fixed Capacity Compressor is activated, the
Copeland Digital Scroll™ Compressor will only be allowed to
modulate within the range of 70% - 100% in order to prevent the
loss of reheat capacity during low load conditions.
If, with both compressors on, the 1st digital compressor has
modulated down to its 70% minimum and the Coil Suction
Temperature falls below the Coil Temperature Setpoint minus the
Cooling Stage Control Window, then the second compressor will
stage off once its Compressor Minimum Run Time and the Stage
Down Delay Timers have been met. At that point, the Copeland
Digital Scroll™ Compressor can modulate down as needed to
maintain the Coil Temperature Setpoint.
If the RSMD has two Digital Compressors, the 1st Compressor
will be locked at 100% and the 2nd Compressor will modulate.
Head Pressure Control
The Refrigeration System Module for Digital Compressors (
RSMD) can monitor a Head Pressure Transducer and control a
Condenser Fan to maintain a Head Pressure Setpoint. The RSMD
must be configured for an Air Cooled Condenser.
A Condenser Relay is commanded on when the first 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.
When the Condenser Signal first 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 Dehumidification Mode, the Condenser Output Signal
controls to the Reheat Head Pressure Setpoint. High Head
Pressure conditions produce the same effects as in the Cooling
Mode.
If no Head Pressure Sensor is detected, the Condenser Output
Signal will be maintained at 100%.