Suction Group - Danfoss AK-PC 551 User Manual

Suction Group

Compressor types
The following types of compressors can be used for regulation:
• Single-step compressors (one can be speed-regulated)
• Compressor with unloaders
• Scroll compressors (one can be a digital scroll)
• Copeland Stream compressor with one unloader (4 cylinders)
• Bitzer CRII compressor with two unloaders (4-cylinders)
Capacity regulation
The cut-in capacity is controlled by signals from the connected
pressure transmitter/temperature sensor and the set reference.
Set a neutral zone around the reference .
In the neutral zone, the regulating compressor controls the
capacity so that pressure can be maintained. When it can no
longer maintain the pressure within the neutral zone, the control-
ler will cut out or cut in the next compressor in the sequence.
When further capacity is either cut out or cut in, the capacity
from the regulating compressor will be modified accordingly
to maintain the pressure within the neutral zone (only where
the compressor has variable capacity).
– When the pressure is higher than the "reference + a half neutral
zone", cut-in of the next compressor (arrow up) is permitted.
– When the pressure is lower than the "reference - a half neutral
zone", cut-out of a compressor (arrow down) is permitted.
– When the pressure is within the neutral zone, the process
will continue with the currently activated compressors.
Control sensor
Normally, a suction group is controlled based on a signal from
the Po pressure transmitter.
If control on a brine, the S4 sensor must be the control sensor. The
Po pressure transmitter must also be installed, as it is used for frost
protection.
The reference
At set or variable reference can be used for regulation. For
example, the variable reference can be used for a night time
increase or Po optimisation. Enter a set point here so that a
contribution from the Po optimisation or night time increase
is added. This contribution can raise or lower the reference,
as determined by the momentary cooling need.
To limit the reference from values that are too high or too low, set
a max. and min. limit.
Load shedding
When the load shedding function is activated, the maximum
permissible compressor capacity will be limited to the set limit.
In this way, the total electrical load in the store is limited.
The threshold value may not be set lower than the compressor's
lowest capacity step/"Start speed".
AK-PC 551 User Guide RS8GY302 © Danfoss 2015-06
Po ref.
Max.
Min.
3