CPC MultiFlex PAK, User Manual

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Compressor Groups PAK Software Overview • 17
6 PAK Software Over-
view
6.1. Compressor Groups
6.1.1. Maximum # of Groups
The maximum number of compressor groups
is eight. Each compressor group corresponds to a
physical relay point on a MultiFlex board. PAK
activates and deactivates compressor groups in
order to control the suction pressure.
The total maximum number of individual
compressors that can be controlled by the PAK is
sixteen, regardless of how many compressor
groups these compressors are associated with.
Compressors are only activated or deactivated as
part of a compressor group; however, a PAK
input may be set up to read the discharge temper-
ature for any or all of the compressor groups.
The number of compressors that may belong
to a single compressor group is limited by the
amperage rating on the MultiFlex output point
(max. 2A up to 240VAC).
Note: When splitting up compressors into
the eight groups, the total compressor HP should
be spread out as much as possible to make use of
as many compressor groups as possible.
6.1.2. Required Setpoints
The setpoints required for compressor group
operation are: Suction Setpoint, Suction Dead-
band, Suction Outer Deadband, and fixed-step
ON and OFF delay times. You will also need to
configure which groups will be ON for each step
in the fixed step strategy.
6.1.3. Compressor Group Stage
Activation and Deactivation
For both Cyclic and Fixed Step compressor
group control strategies, the setpoints required
are:
Suction Setpoint. The suction pressure you
wish to maintain.
Suction Deadband. A small range of values
equally above and below the Suction Setpoint,
within which the suction pressure will be consid-
ered to be acceptably near the Suction Setpoint
and no stage activation or deactivation will
occur.
Step ON and OFF delay times. The Step ON
delay time is observed immediately after the
PAK adds compressor capacity (either by
cycling ON a larger number of compressors or
by incrementing up one step in the Fixed Step
strategy). If after bringing ON more compressors
the suction pressure is still above the top part of
the Suction Deadband, it must wait an amount of
time equal to the Step ON delay before consider-
ing a
Suction Outer Deadband. A larger range of
values equally above and below the Suction Set-
point (larger than the Suction Deadband). The
Suction Outer Deadband seeks to prevent an
unnecessary activation or deactivation of com-
pressor group stages in instances where the suc-
tion pressure is just barely outside of the Suction
Deadband and already moving back toward the
setpoint.
When the suction pressure lies somewhere
between the inner and outer deadband, it ana-
lyzes the direction and rate of change of the suc-
tion pressure over the last 1/2 of the Step ON or
Step OFF delay (depending on the direction). If
the calculated slope of the suction pressure dur-
ing the last 1/2 of the delay indicates the suction
pressure will return to within the Suction Dead-
band range in an amount of time equal to an
additional Step ON or Step OFF delay, it will
delay compressor stage changing for one delay
period.
Example: a PAK has a suction setpoint of
45PSI, a Suction Deadband of 4PSI, a Suction
Outer Deadband of 8PSI, and a Step ON and
Step OFF delay of 30 seconds each. With all