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Fixed Sequence—Compressor 2 /
Compressor 1
If the chiller is in the Auto mode and all interlocks have
been satisfied, Compressor 2 will be started based on
the leaving water temperature rising above the
"Differential to Start" setting. Compressor 1 will stage
on when the overall chiller average capacity exceeds
stage on load point for 30 seconds. The stage-on load
point is adjustable up to 50 percent.
The default is 40 percent which means that a single
compressor would have to load to 80 percent (the
average would be 40 percent) before the second
compressor starts. Both compressors will run until
chiller average capacity drops below stage-off load
point for 30 seconds. The stage-off load point is also
adjustable. Compressor 1 will be shut down and
Compressor 2 will run until water temperature drops
below the differential to stop. Before shutting down,
Compressor 1 will be unloaded and Compressor 2 will
be loaded to maintain the same average capacity
command. If chilled water reset is used, the upstream
compressor usually will be the most efficient
compressor to operate at part load. If the leaving water
temperature is reset and the chiller only needs one
compressor, then the upstream compressor would be
running closer to its selection point and will be the
most efficient compressor to operate.
Figure 51. Duplex™ chiller sequence of operation:
lead 2 / lag 1
Evap LWT Falls
Below
Differential to
Stop
Running
(Circuit 2)
Chiller Capacity
Less than 30%
(De-Energize
Cprsr with Most
Starts and Hours)
Running
(Circuit
1 and 2)
Sequencing—Balanced Starts and Hours
When desired to balance the wear between the
compressors, this method will extend the time between
maintenance on the lead compressor. When balanced
starts and hours is selected, the compressor with the
fewest starts will start. If that compressor is unavailable
to start due to a circuit lockout (including restart inhibit)
or a circuit diagnostic, then the other compressor will
be started. The second compressor will stage on when
CDHF-SVX01N-EN
Auto
Evap LWT Rises
Above Diff to
Start (Start Cprsr
with Fewest
Starts and Hours)
Single Comp
Capacity Greater
than 80% (No
Time Delay)
chiller capacity exceeds the stage-on load point for
30 seconds. When chiller capacity falls below stage-off
load point for 30 seconds, the compressor with the
most hours will be shut off.
Figure 52. Duplex™ chiller sequence of operation:
equalize starts and hours
Evap LWT Falls
Below
Differential to
Stop
Running
(Single Circuit)
Chiller Capacity
Less than 30%
(No Time Delay)
Running
(Both Circuits)
Chiller Start Initial Capacity Command
If the Chiller Start Initial Capacity Command is set
greater than the Staging On Boundary, both
compressors will cycle on similar to a Combined
Staging Sequence and both compressors will load up
to the initial capacity command. If there is a reduction
in load, the lag compressor will shut off based on the
staging sequence chosen. The simultaneous start
feature only applies when both compressor are off.
This feature is intended to allow a Duplex™
CenTraVac™ chiller to start and load quickly for
customers that require quick restart after a power
failure.
O O p p e e r r a a t t i i n n g g P P r r i i n n c c i i p p l l e e s s
Auto
Evap LWT Rises
Above
Differential to
Stop
Compressor A
Capacity Greater
than 80%
(No Time Delay)
69
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