QUANTUM™ HD COMPRESSOR CONTROL PANEL
OPERATION
090.040-O (MAR 12)
Page 47
Capacity Mode -
• Manual
• Automatic
• Remote Comm
• Remote 4-20
• Remote IO
• Remote Seq.
Minimum Capacity - This is the capacity that a
compressor will load to when it is started. It will
remain at or above this capacity until it is com-
manded to stop.
NOTE: The Compressor Mode and Capacity Mode
listed above should both be set to Remote Seq. for
complete execution of the sequencing system by
the leader to occur.
The following is a description of the Sequencing strategy:
Start/Stop
System Setup:
• Control Input – Suction Pressure
• Control Direction – Forward
• High Stage Link – Disabled
Start Procedure
Before starting a compressor, the leader must
determine that all running compressors are load-
ed and that the Suction Pressure has risen to a
point where an additional compressor is needed.
First, the l
eader checks that either no compres-
sors are running or all the running compressors
average 90% capacity. If a running compressor is
at less than 90% capacity but is in a Load Inhibit
or Force Unload condition, for the purposes of
this calculation it is assumed to be at 90% ca-
pacity.
If all the running compressors are loaded the
leader next begins comparing its Suction Pres-
sure to the Autocycle Start setpoint. When the
Suction Pressure rises above the Start setpoint,
the start timer is initiated. If the start timer
reaches the Autocycle Start Delay setpoint time
and the Suction Pressure has remained above
the Start setpoint for the entire time, the leader
attempts to start an additional compressor. If the
Autocycle Start Delay setpoint is 0 minutes, the
leader still waits 15 seconds before starting a
compressor.
To determine which compressor to start, the
leader first sorts all the compressors in the sys-
tem based on their start number, low to high. If
two compressors have the same start num-ber,
the first one on the list remains ahead of the
second. Next, the leader starts at the top of the
list and works down through list until it
fi
nds a compressor that is available to run. To be
deemed available, a compressor must have good
sequencing communications and its Compressor
Mode and Capacity Mode must be set as Remote
Sequencing. In addition the compressor must
be off, and it cannot be in a Start Inhibit
condition except for the Start Inhibit Slide
Value Too High condition. The compressor with
the lowest start number that also meets these
conditions is then sent a start command. If no
compressors are currently available to start,
the leader will continue checking until one
becomes available or until the Suction
Pressure drops below the Start setpoint.
After a compressor has been sent a start com-
mand, the leader waits for that compressor to
reach a Running state. If 3 minutes passes and
the compressor has not yet begun to run, the
leader sends it a stop command. This com-
pressor is then flagged as Unable to Start for 1
hour. After that time the leader may again try to
restart the compressor if additional capacity is
needed. After a compressor begins running, or
after one fails to start and is sent a stop com-
mand, the leader can begin the process of start-
ing another compressor.
Stop Procedure
If the Suction Pressure drops to a point where
one of the running compressors is no longer
needed, the leader will stop the last compressor
in the sequence list.
When the Suction Pressure drops below the Au-
tocycle Stop setpoint, the stop timer is initiated.
If the stop timer reaches the Auto
cycle Stop De-
lay setpoint time and the Suction Pressure has
remained below the Stop setpoint for the en-
tire time, the leader attempts to stop one of the
running compressors. If the Autocycle Stop De-
lay setpoint is 0 minutes, the leader still waits 15
seconds before stopping a compressor.
To select the compressor to stop, the leader also
sorts all the compressors in the system accord-
ing to their start number. Then the leader starts
at the bottom of the list and works up, looking
for a running compressor that can be stopped.
To be selected a compressor must have good
sequencing communications and its Compres-
sor Mode and Capacity Mode must be set as Re-
mote Sequencing. In addition, the compressor’s
run time must be greater than the compressor’s
Minimum Run Time setpoint. If the Minimum
Run Time setpoint is 0 minutes, a compressor
can also be stopped if it is still in Starting mode.
The compressor with the highest start number
that meets these conditions is sent a stop com-
mand. If no compressors are currently available
to stop, the leader will continue checking until
one becomes available or until the Suction Pres-
To Next Page
Loading...
