AIR COOLED CHILLERS
TYPICAL MICROPROCESSOR CONTROLLER
(OPTIONAL)
29
Sequence of Operation
STAGE - ON SEQUENCE
STAGE - OFF SEQUENCE
The following describes the sequence of operation for a two compressor reciprocating 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 control contact closed, if any.
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 & unloader solenoid (lead compressor only) shall be switched ON.
The first stage of capacity is now on-line.
The unitis now at 25% capacity .
As discharge pressure of compressor #1 rises, the corresponding fans energized according to the fans 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:
After a minimum interval, if the leaving water temperature is greater than the stage 2- ON water temperature set point
value, compressor #1 unloader shall be de-energized.
Compressor #1 will now be fully loaded.
The unitis now at 50% capacity .
Stage #3:
After a minimum time delay and if the leaving water temperature is greater than the stage 3 - ON water temperature set
point value, compressor #2 & the liquid line solenoid of the circuit #2 is switched on. Also the compressor #1 will be
unloaded.
The third stage of capacity is now achieved.
The unitis now at 75% capacity .
As the discharge pressure of compressor #2 rises, the corresponding fans energized according to the fan stage-ON set
point.
Stage #4:
If the leaving water temperature is greater than the stage 4 - ON water temperature set point value, the compressor #1
unloader shall be de-energized.
The unitis now operatingat 100% capacity .
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 4 -OFF water temperature
set point value, stage 4 is turned off. Compressor #1 unloads.
If the leaving water temperature falls below the stage 3-OFF water temperature set point value, the stage 3 is turned off.
The liquid line solenoid #2 is turned off and compressor #1 is loaded up to 100%.
When compressor #2 suction pressure falls below the pump down set point value, compressor #2 and the corresponding
fans are turned off. The unit is now at 50% capacity.
Stage 2 and 1 are turned off in a similar manner to stages 4 & 3 mentioned above.
When the compressors are in the standby or OFF mode, pump down of the chiller is maintained. If the suction pressure
rises above the pump down set point value the compressor will turn on with the liquid line solenoid closed. When the
suction pressure falls below the pump down set point value, the compressor will be turned off.
