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Compressor
Control
Compressors--The
EPC-2000 is capable of
controlling a rack with up to
eight parallel fixed-speed
compressors or six parallel
compressors and two satellite
compressors. The parallel
compressors will be activated
based upon one of two suction
pressure setpoints with a
heuristic algorithm.
Staging--The
compressor staging method can be
set for sequential staging,
random (round-robin) staging, a
combination of sequential and
round-robin, or by custom staging
steps programmed by the user via
a mix match table.
Sequential--The
compressors will be activated and
deactivated in a FILO format, the
first compressor on will be the last
compressor turned off.
Round-Robin--The
compressors will be activated and
deactivated randomly in order to
maintain even compressor run times
over a 24 hour period. Each
compressor will be activated at least
once every two hours to prevent the
lubrication oil from migrating out of
the compressor.
Combination
of Sequential and Round-Robin--For
parallel racks with two different
sizes of compressors or one
compressor with an unloader. It will
activate the sequential compressors
via the FILO format, then will
activate the round-robin compressors
randomly. The sequential compressors
will be de-activated last.
Mix
Match--On parallel
racks with different compressor
sizes. The user sets the order of
which the compressors will activate
and de-activate in order to smooth
the rack operating step sizes.
Unloaders--The
EPC-2000 can operate up to eight
unloaders per rack. Each unloader
can be assigned to any of the
parallel compressors. The
unloaders will operate on an
accelerated algorithm as compared
to the compressor algorithm. When
a compressor with an assigned
unloader is activated, the
compressor will initially start unloading. If the EPC-2000
requires an increase in the rack
load, the compressor will then be
fully loaded before an additional
compressor is activated.
Compressor Swing
Staging--When the rack
is set up to run in a combination
of sequential and round-robin
mode, the first sequential
compressor will operate as the
swing compressor. This
compressor, usually a smaller
compressor, will be activated
prior to the activation of one of
the round-rob in (bigger)
compressors. The smaller
compressor will act as a half
step, smoothing out the
performance of the rack.
Mechanical Back-Up--Mechanical
pressure controls can be
installed on the rack and operate
in two different methods:
Series Switchback--The
EPC-2000 is configured to operate the
compressors by de-energizing the
control relays. The mechanical low
pressure control is wired in series
with the EPC-2000 control relay. If
the control fails, all compressor
relays will be activated and the low pressure mechanical controllers
will cut out the compressors when the
suction goes below their settings.
NOTE: This method is only possible
with the addition of a timing relay
in series with the compressor
contactor coil voltage to prevent
short cycling on start-up.
Parallel
Switchback--The
EPC-2000 is configured to operate the
compressors by energizing the control
relays. The mechanical low and high
pressure controls are wired in
parallel to the EPC-2000 with the
line voltage to the backup wire
through an energized
"Switchback" relay on the
EPC. if the EPC fails, all EPC
control relays are de-energized, the
Switchback relay is de-energized and
power is switched to the backups. The
mechanical backup controls now
operate the compressors based upon
their Cut-In and Cut-Out settings.
With this method, the backup settings
can be set to run the rack as closely
to the suction Setpoint as possible.
Split Suction, Two-Stage
Suction--The EPC-2000
can control a parallel rack with
up to two suction groups. Each
suction group compressors may be
staged differently. If the rack
is configured as a two-stage
rack, the high side suction group
compressors will activate prior
to the low side suction group
compressors.
Defrost Recovery--The
Compressor Heuristic Algorithm
will accelerate the staging of
the compressors immediately
following the termination of a
gas defrost circuit.
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