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MICROPROCESSOR CONTROLLER
Sequence of Operation
The following describes the sequence of operation for a two screw compressor chiller unit.
Operation is similar for a one or four compressor unit.
For initial start-up, the following conditions must be met:
·
All power supplied to the unit shall be energized for 12 hours.
·
Control power switch on for at least 5 minutes.
·
All safety conditions satisfied.
·
Press ESC on the microcomputer keypad.
·
Chilled water pump running and chilled water flow switch contact closed.
·
Customer interlock contact closed, if any.
STAGE - ON SEQUENCE
Staging ON & OFF sequence, shall be accomplished by the Leaving water temperature control selection.
Stage #1:
If the Leaving Water Temperature is greater than the Stage 1- ON water temperature set point value, the Compressor #1
liquid line solenoid & slider control valves shall be switched ON. Now the compressor is in the minimum or unloaded
capacity. The compressor capacity is varied to achieve the full/part load capacity as per the load demand.
As discharge pressure of Compressor #1 rises, the corresponding fans are energize accordingly to the fan stage-ON set
point. If the discharge pressure falls below the fan stage-OFF set point value, the corresponding fans will turn off.
Stage #2:
If the Leaving Water Temperature is greater than the Stage 2- ON water temperature set point value, the Compressor #2
liquid line solenoid & slider control valves shall be switched ON. Now the compressor is in the minimum or unloaded
capacity. The compressor capacity is varied to achieve the full/part load capacity as per the load demand.
As discharge pressure of Compressor #2 rises, the corresponding fans are energize accordingly to the fan stage-ON set
point. If the discharge pressure falls below the fan stage-OFF set point value, the corresponding fans will turn off.
STAGE - OFF SEQUENCE
During the staging OFF, the first-in last-out sequence is adopted, if equalization of compressor timing is not selected.
Else the more used is switched off.
As the applied load decreases and when the leaving water temperature falls below the stage 2 -OFF water temperature
set point value, stage 2 is turned off.
If the leaving water temperature falls below the stage 1-OFF water temperature set point value, the stage 1 is turned off.
