QUANTUM™ HD COMPRESSOR CONTROL PANEL
OPERATION
090.040-O (MAR 12)
Page 48
sure rises above the Stop setpoint.
After a compressor has been sent a stop com-
mand, the leader waits for that compressor to
go to off. If 3 minutes passes and the compressor
has not yet turned off, the leader then flags this
compressor as Unable to Stop for 1 hour. After
that time the leader
may again try to stop the
compressor. After a compressor goes to off or
after one fails to stop within 3 minutes, the
leader can begin the process of stopping
another compressor.
Load/Unload
System Setup:
• Control Input – Suction Pressure
• Control Direction – Forward
• High Stage Link – Disabled
Load Procedure
If the leader compressor’s Suction Pressure is
above the Capacity Control setpoint, the
leader calculates the increase in capacity that is
required. The calculation is as follows:
Difference = Suction Pressure – (Capacity Con-
trol Setpoint + Upper Dead Band)
If the Difference
is less than the Upper Propor-
tional Band:
Capacity Change = (Difference / Upper
Proportional Band) * Upper Cycle Time
If the Difference is greater than the Upper Pro-
portional Band:
Capacity Change = Upper Cycle Time
After the capacity increase has been calculated,
the leader then fi
nds the compressor whose ca-
pacity should be changed. To make this deter-
mination, the leader sorts all the compressors
based on their start number. Beginning at the
compressor with the lowest start number, the
leader finds the first compressor on the list that
is running but is not at its maximum capacity. A
compressor is at maximum capacity if it is at
100 percent capacity or if it is in a Load Inhibit
or Force Unload condition.
If the selected compressor is running the Quan-
tum™ HD software, the capacity increase is
added to the compressor’s current capacity. This
new value is then sent to the compressor as its
Capacity Command, and that compressor will try
to increase its capacity to match the Command
value.
If the selected compressor is controlled by a
Quantum™ 1-4
or a Plus panel, the capacity
increase is interpreted as the time period for a
load pulse and is sent to the compressor as
a load command. The follower compressor
will then turn on its load output for the given
number of seconds.
Unload Procedure
If the leader compressor’s Suction Pressure is
below the Capacity Control setpoint, the leader
calculates the decrease in capacity that is re-
quired. The calculation is as follows:
Difference = (Capacity Control Setpoint -
Upper Dead Band) – Suction Pressure
If the Difference is less than the Lower Propor-
tional Band:
Capacity Change = (Difference / Lower
Proportional Band) * Lower Cycle Time
If the Difference is greater than the Lower Pro-
portional Band:
Capacity Change = Lower Cycle Time
After the capacity decrease has been calculated,
the leader then fi
nds the compressor whose
capacity should be changed. To make this de-
termination, the leader sorts all the compres-
sors based on their start number. Beginning at
the compressor with the highest start number,
the leader finds the last compressor on the list
that is running and whose capacity is above its
Minimum Capacity setpoint. If two compressors
are currently running at or below their Minimum
Capacity setpoints, the leader will not allow any
additional compressors to unload. This will al-
low the Suction Pressure to continue to drop
and will cause the leader to turn off one of the
unloaded compressors. If the leader sees that
only one compressor is running in its system, it
will continue to unload the compressor down to
the leader's Automatic Capacity Mode Minimum
Slide Valve Position setpoint.
If the selected compressor is running the Quan-
tum™ HD software, the capacity decrease is sub-
tracted from the compressor’s current capacity.
This new value is then sent to the compressor as
its Capacity Command, and that compressor will
try to decrease its capacity to match the Com-
mand value.
If the selected compressor is controlled by a
Quantum™ 1-4 or a Plus panel, the capacity de-
crease is interpreted as the time-period for an
unload pulse and is sent to the compressor as
an unload command. The follower compressor
will then turn on its unload output for the given
number of seconds.
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