Trane CenTraVac Duplex CDHE, Operation & Maintenance Manual

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17
CDHF-SVU01C-EN
General
Information
Duplex Compressor Sequencing
Four methods (Two fixed sequence
methods, a balanced start and hour’s
method, and a no staging method)
are provided for order of a
compressor sequencing on CTV
Duplex chillers. The desired method
is selectable at startup via the service
tool. The application can decide to
either balance the wear burden
among the unit’s compressors, to
start the most efficient compressor,
or to simultaneously start and stop
both compressors to minimize
startup pull down time. Each method
has specific applications were it can
be used advantageously.
If one compressor is locked out, in
restart inhibit, or generally not ready
to start, the available compressor will
be started.
Note: The following description
assumes compressor 1 is the down
stream compressor.
Fixed Sequence – Compressor 1/
Compressor 2 (Default mode)
If the chiller is in the Auto mode and
all interlocks have been satisfied,
compressor 1 will be started based
on the leaving water temperature
rising above the “Differential to Start”
setting. Compressors 2 will stage on
when the overall chiller average
capacity exceeds Stage ON Load
point for 30 seconds. The stage on
load point is adjustable (via service
tool) up to 50%. The default is 40%
which means that a single
compressor would have to load to
80% (the average would be 40%)
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 (via service tool) (default =
30%, range from 0 to 50%).
Compressor 2 will be shut down and
compressor 1 will run until water
temperature drops below the
differential to stop. Before shutting
down, compressor 2 will be
unloaded and compressor 1 will be
loaded to maintain the same average
capacity command.
When running chilled water
temperature at selected conditions,
the downstream compressor usually
will be the most efficient compressor
to operate at part load because
compressors on Duplex chillers are
not sized exactly the same.
Figure 12. CDHF/G sequence of operation: lead 1/lag 2