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User Guide
Capacity controller
AK-PC 651
ADAP-KOOL® Refrigeration Control System
User Guide
|
Capacity Controller, AK-PC 651
Introduction
Application
The controller is used for capacity regulation of compressors
and condensers in small refrigeration applications. A maximum of
10 compressors and one condenser can be regulated. For exam-
ple:
• One suction group + one condenser group (max. 15 steps)
• One compressor group, max. 10 steps
• One condenser group, max. 8 steps
Advantages
• Energy savings via:
- Optimisation of suction pressure
- Night time increase
- Floating condensing pressure
- Load limitation
Input and output
There are a limited number of available inputs and outputs.
For each signal type, though, the following can be connected:
• Analogue inputs, max. 10 pcs.
Signal from pressure transmitters, temperature sensors,
voltage signal, etc.
• Digital inputs, max. 18 pcs.
Signal from automatic safety control, day/night signal, etc.
• Relay outputs, max. 13 pcs.
Connection of compressors, condenser fans
• Solid state outputs, max. 2 pcs.
- Control of capacity valve on a Copeland digital scroll
- Control of unloaders on a Copeland stream compressor.
- Control of unloaders on a Bitzer CRII Ecoline compressor
If the outputs are not used for these functions, they can be used
as ordinary relay outputs
• Analogue outputs, max. 4 pcs.
Speed control of compressors or condenser fans.
Operation
The daily operation can be set up directly on the controller or
via an external display device.
During set-up, the display images will be adjusted so that only
the relevant images are opened for additional setting and
end-user operation.
The operation is password protected, and three levels of
access can be granted.
The controller contains several languages. Select the preferred
language at start-up.
Data communication
The controller has built-in modbus data communication, and it
can be connected to a system device in the AK-SM 800 serie.
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© Danfoss | ADAP-KOOL® | 2017.07
User Guide
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Capacity Controller, AK-PC 651
Suction Group
Compressor types
The following types of compressor combinations can be used for
regulation:
• Several single-step compressors
• One speed controlled compressor + single-step compressors or
multi -step compressors
• One Digital scroll compressor + single-step compressors or multi
-step compressors
• One Copeland Stream Compressor (4 or 6 cylinders) + single-step
or multi-step compressors
• Bitzer CRII compressor (4 or 6 cylinders) + single-step or multi-
step compressors
• One multi-step compressor + single-step compressors
• Several multi-step compressors with the same number
of unloaders
In the combinations where the first compressor is different from
the others, it may be of a different size than the subsequent
single-stage compressors.
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.
Po ref.
Max.
Min.
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User Guide
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Capacity Controller, AK-PC 651
Condenser
Fan control
The fans can be controlled incrementally using the controller’s
relays, or they can be speed-controlled via the controller’s
analogue output.
Speed control can be via a frequency VLT-type converter.
If the fans have EC motors, the 0-10 V signal can be used directly.
Step and speed simultaneously. (Parallel signals in step with each
other.) This function is primarily used to control
a frequency converter, but if the frequency converter fails,
external wiring will switch over to step control.
During night operation, the noise level of the fans can be kept
down. This is done by limiting the cutin capacity.
For speed control, keep the number of revolutions low.
Omit step cutin for step-by-step activation.
The limitation is bypassed if safety functions Sd max. and
Pc max. start to function.
Control
Regulation is carried out based on a signal from the Pc pressure
transmitter or an S7 media temperature sensor. The signal is com-
pared with the regulation reference.
The regulation reference can originate from one or more of the
following functions:
• Fixed reference
• Variable reference, which follows the outdoor temperature.
When the outdoor temperature drops, the reference will drop
by a corresponding amount.
This variable reference requires the installation of an Sc3
outdoor temperature sensor. The sensor must be positioned so
that it registers the correct outdoor temperature. In other words,
it must be shielded from direct sunlight and located near the
airway of the condenser.
This regulation requires setting a min. and max. reference, so
that the regulation process is kept within the given limits.
• Increase the reference for heat recovery.
Here the reference is raised to a fixed value when a signal is
received on a DI input. The reference value can be higher than
the set max. reference.
When the temperature of the heat recovery has been reached
and the DI signal disappears, the reference will drop once again,
though it will do so over the course of a few minutes to prevent
abrupt changes in the reference.
Media temperature
If controlling a media temperature, the control sensor
must be set to S7. This temperature sensor must be located
in the desired medium.
The Pc pressure transmitter must also be installed. It is used for
high-pressure monitoring.
Max. ref.
Min. ref.
Ref. for heat recovery
Temperature sequence for
heat recovery
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User Guide
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Capacity Controller, AK-PC 651
Safety functions
Min./max. suction pressure Po
The suction pressure is recorded continuously.
If the measured value falls below the set minimum limit, the
compressors will immediately cut out.
If it exceeds the max. value, an alarm will be generated once
the time delay has elapsed.
Sensor failure
If lack of signal from one of the connected temperature sensors or
pressure transmitters is registered an alarm will be given.
• In the event of a Po error, regulation will continue with a set
capacity in daytime operation (e.g. 50%), and a set capacity in
night operation (e.g. 25%), but with a minimum of one step.
• In the event of a Pc error, the condenser capacity that
corresponds to how much compressor capacity is connected
will cut in. Compressor regulation will remain normal.
• When there is an error on the Sd sensor the safety monitoring of
the discharge gas temperature will be discontinued.
• When there is an error on the Ss sensor the monitoring of the
superheat on the suction line will be discontinued.
• In the event of an error on the outdoor temperature sensor,
Sc3, the permanent setting value will be used as a reference.
• In the event of an error on the S4 sensor, regulation will continue
with the Po signal, but the reference will be lowered by 5 K.
• In the event of an error on the Saux sensor, the thermostat
output will go to the rest position.
NB: A faulty sensor must be OK within 10 minutes before a sensor
alarm is cancelled.
A sensor alarm can be reset manually by pushing the
"X-button" for 2 seconds when the alarm is shown in the display
"Active alarms".
Max. condensing pressure Pc
If the condensing pressure reaches the upper permissible value
(3 K below limit), the controller will connect all condenser fans
to keep the pressure down. At the same time, a portion of
the compressor capacity will be disconnected. If the pressure
remains near the threshold value, even more compressors will be
disconnected.
All compressors will be disconnected immediately if the threshold
value is exceeded.
LP switch
On/off signal on a DI input
If a signal is received, all compressors will immediately be stopped.
HP switch
On/off signal on a DI input
If a signal is received, all compressors will immediately be stopped.
Fan capacity will increase depending on how much the
Pc measurement exceeds the reference.
General DI alarms
On/off signal on a DI input
The regulator contains three general alarm inputs, to which alarm
text and delay times can be connected.
Alarm and text will appear when the delay time has elapsed.
Min./max superheating via Ss measurement
Temperature sensor on an AI input.
If superheating is higher or lower than the set limits, an alarm will
be generated once the time delay has elapsed.
General thermostat
It is possible to install one general thermostat if there is a relay
output and an analogue input available.
Max. discharge gas temperature Sd
Temperature sensor on an AI input.
A signal can be received from a Pt 1000 Ohm sensor on the
pressure pipe.
• Common Sd for the whole compressor group
If the temperature nears the set max. temperature, the capacity
of the compressor will be reduced
• Compressor Sd
if it is an Sd from a Copeland digital scroll, a Copeland stream or
Bitzer CRII the capacity will be increased so that the compressor
can cool down itself ).
The compressors will be stopped if the temperature reaches the
set max. temperature value.
© Danfoss | ADAP-KOOL® | 2017.07
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