Daikin Pathfinder AWV Installation, Operation And Maintenance Manual page 69

the target should be allowed to drop by 0.1°C. Increases to
the condenser target value will happen as often as the target
calculation requires. These requirements ensure the running
compressor is given a chance to unload in compensation for
adding WSE capacity.
Fan Control - All Fans with VFD
If Fan VFD Configuration is set to All Fan VFD, different control
logic will be used. All fan motors are ECM/DC fan motors which
have integrated inverters and are controlled via modbus. This
configuration requires the DC Fan Controller.
System Architecture
Architecture of the control system components involved in
control of the ECM/DC fan motors is shown below. Data flows
in both directions on the communication link as well as the
Modbus connection.
Figure 73: Controller Communication Architecture
Unit Controller
Fan Motors
The following control logic will reside in the DC Fan Controller:
• Automatic control
• Alarm handling per individual fan motor
• Fan motor addressing process
• Fan motor testing control
Normal Control
When Control Mode is set to Auto, the logic in this section will
automatically control the ECM/DC fan motors for normal chiller
operation.
The VFD speed should always be 0% when the fan stage is 0.
When the fan stage is greater than 0, the VFD speed will be
calculated to control the saturated condenser temperature to
the VFD target.
Speed Command To Motors
All fan motors will be sent a speed command via modbus. The
speed command is in units of rpm with 800 rpm corresponding
to 100% and will vary based on the percent speed calculation.
Speed Command = Percent Speed Calculation x 8
Normally the same speed command is sent to all motors on a
circuit.
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DC Fan Controller
Modbus
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Staging
Calculated RPM is a value used in the fan staging logic.
When the circuit run flag is 0, the fan stage is always 0. Once
the fan stage is more than 0, it will not be allowed to drop back
to 0 until the circuit run flag is 0.
The maximum fan stage is equal to the number of fans on the
circuit. When fan stage is 0, it will be set to the maximum fan
stage when the PI (proportional integral)loop reaches 100%.
This does not occur any time other than when the fan stage is
0.
Test Mode Control
When Control Mode is set to Test, the fan motors can be
manually controlled for test purposes.
The test settings allow selecting values from 0% to 100%.
When the test setting for a fan is set to 12.5% or higher, the
speed command corresponding to the test setting will be sent
and the run command will be sent to the fan.
Speed Command = Test setting x 8
When Control Mode is no longer set to Test, the following
actions should occur:
• all the test settings set back to 0%
• stop command sent to all motors
• speed command of 0 rpm sent to all motors
Evaporator EXV Control
This section outlines the positioning logic for the Evaporator
EXV, which is the EXV installed in the liquid line feeding the
evaporator.
• EXV will initially be positioned to control evaporator
pressure
• EXV will normally be positioned to control SSH (suction
superheat)
• SSH target will vary based on DSH (discharge superheat)
• In some conditions, EXV will be positioned to control
evaporator pressure to keep all parameters within
operating envelope
There are five EXV control states:
• Closed – EXV is closing or in the closed position
• Preopen – EXV is opening prior to compressor start
• Start Pressure Control – EXV is controlling to pressure
target after compressor start
• SSH Control – EXV is controlling suction superheat
• MOP Control – EXV is controlling to maximum operating
pressure for compressor
Closed State
If the unit is configured without liquid line solenoid valves, the
EXV position should be 0% any time the EXV is in a closed
state. The 0% position command also causes the evaporator
EXV module driver to re-initialize the valve to the zero position.
IOM 1242-8 • PATHFINDER
Circuit Functions
MODEL AWV CHILLERS
®