Danfoss ADAP-KOOL AK-PC 572 User Manual
User Guide
Capacity controller for CO
mini pack
AK-PC 572
ADAP-KOOL® Refrigeration Control System
Introduction
Application
The controller is used for capacity regulation of compressors
and gas cooler in small CO2 refrigeration applications.
As a minimum, control of a condensing unit can be performed
using one compressor unit, one gas cooler and one receiver.
A maximum of 3+2 compressors can be regulated.
Fx:
Advantages
• Energy savings via:
- Optimal control of CO
- Optimisation of suction pressure
- Night time increase
- Floating gas cooler reference
- Heat recovery
- Load limitation
• Simplified setting of the functions
The controller ensures that the different control settings are
adjusted in accordance with one another. Only basic settings are
required.
• Ongoing adjustment of control references
Newly developed algorithms adjust the problematic pressure
ratios in the CO2 controller.
Input and output
There are a limited number of available inputs and outputs so
most connections are intended for one specific function.
However, there a few options for AUX use:
• If only one or two compressor units are connected to the MT
circuit, there will be a DI input available. This could, for example,
be used as an alarm input.
• If the compressor used is not a Bitzer CRII, a solid state output
can be used for oil management.
• If heat recovery is not used, the AUX3 function can be used for an
alarm function.
2
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 an AK-SM 800 type system device.
In order to control the high pressure valve and receiver pressure
valve, two valve driver modules, type EXD 316, must be connected.
The overview of connections can be seen on page 22.
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Suction Group
Compressor types
The following types of compressors can be used for regulation:
• Single-step compressors (one can be speed-regulated)
• Bitzer CRII compressor with two unloaders (4-cylinders). MT only.
Capacity regulation
The cut-in capacity is controlled by signals from the connected
pressure transmitter and the actual reference.
In the absence of any reference there is a neutral zone of up to 5 K.
– 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.
This is always controlled using the "Best fit" connection pattern.
The reference
The controller will be set based on a fixed reference point.
Based on the configured reference, the controller will permit an
offset of up to +/- 8K depending on the other control parameters.
For example
- Night-time increase. Fixed 5 K (on the MT circuit only)
- Po optimisation (on the MT circuit only)
Po ref.
8 K
8 K
Load shedding
The function is activated from the system unit.
When the load shedding function is activated, the maximum
permissible compressor capacity will be limited to 50% of
maximum on both MT- and LT circuits.
In this way, the total electrical load in the store is limited.
Control parameters
To make it easier to start up the system, we have grouped the control parameters into a number of experience-based values. These
values have been combined in a setting called "Easy-settings".
Here you can choose between a set of control settings applicable
to a slow to rapidly reacting system.
The factory setting is medium.
Oil management
If the DO6 output is in use by a CRII, oil management cannot take
place. If the output is available, the controller can pulse oil into the
MT circuit. The time between the pulses can be configured using a
timer function or using a signal from a level switch.
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Liquid injection in the MT suction line
This function is possible only if there is an available DO output.
The function opens for liquid when:
• The suction temperature is too high
• The pressurised gas temperature is too high
• Liquid inlet to the compressor must be prevented.
Gas cooler
Fan control
The fans must be speed controlled by the controller's analog
output.
EC motors can receive the 0-10 V signal directly.
During night operation, the noise level of the fans can be kept
down. This is done by limiting the voltage and thus the speed.
The limitation is bypassed if safety function Sd max. start to
function.
De-super heater
This function is possible only if there is an available DO output.
This function activates a fan so that the pressurised gas temperature in the LT circuit can be lowered:
• The fan stops when the outdoor temperature is low
• The fan stops when the MT suction gas is too low
Regulation
The controller regulates the pressure in the gas cooler (condenser)
so that the system achieves the optimal COP.
The controller will always optimise to a subcritical state.
The pressure in the gas cooler is controlled by the valve Vhp.
Regulation must have inputs from both a pressure transmitter Pgc
and a temperature sensor Sgc. Both must be fitted in the outlet
immediately after the gas cooler.
The valve is an CCMT valve, which has been specially developed
for the pressure conditions that exist in a transcritical CO2 system.
The valve's degree of opening can be restricted both at the
closing point and in the entire open point.
Maximum COP control
During normal operation without override, the controller will
maintain the optimum pressure in the transcritical area.
Reference
It is controlled using variable references.
An outdoor temperature sensor, Sc3, must be installed.
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.
Under normal operations it will be controlled using a fixed temperature reference of 3 k above the outdoor temperature.
The pressure reference will be the configured value for the subcooling when adjusting in the sub-critical range, and will be adjusted based on optimal COP when adjusting in the trans-critical
range.
Important
This sensor must be placed
immediately at the gas
cooler outlet.
The reference value will be user-configured during heat recovery.
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Heat recovery
A digital input can be received.
When the signal is received, the reference for the gas cooler will
be raised to the configured value.
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.
A potential relay outlet can be connected to heat recovery. The
potential relay is activated when the controller allows for heat
recovery.
Cooling will always have a higher priority than heat recovery. If
this higher priority occurs, the potential relay will be deactivated
and the reference for heat recovery will be removed from the
controller.
The cooling reference is now used for regulation until the tempe-
ratures and pressure allow for heat recovery to resume.
During heat recovery, regulation can be carried out in accordance
with:
• Max. COP - Most energy-optimal.
• Max. HR - The highest achievable temperature.
Pgc ref
DI
Warning
Remember that the controller controls the gas pressure. If the
regulation is stopped by the internal or external main switch, this
control will stop as well.
Risk of loss of charge.
Receiver control
The receiver pressure can be controlled so that it is kept at the
desired reference point. This reference point is fixed at 6 bar above
the reference point for Po-MT. This control requires the installation of an receiver valve Vrec and a pressure transmitter.
Hot gas dump
This function is possible only if there is an available DO output
This function allows for hot gas to be passed to the receiver if the
pressure approaches Po-MT.
Hot gas will be shut off again when the pressure returns above the
desired level.
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AUX functions and limitations
AUX1-DI and -DO
This function shares an input and output with an MT compressor
3.
AUX1 is possible only if regulating using one or two compressors
on the MT.
AUX1-DI can then be used as an alarm input.
AUX1-DO can then be used for liquid injection, DE-SH or hot gas
dumping.
DO6
The output is a solid state output and reserved for a CRII. If not
regulating using a CRII, DO6 can be used to control an oil valve.
Oil management.
Oil management will share an output with a CRII compressor.
Oil management can take place only if not regulating with a CRII.
Oil management can be performed with a timer function or with
a level signal from an oil receiver. This signal can only be included
in the "OIL" input. If the input is not used for OIL it will be available
and called AUX2-DI. It can then be used as an alarm input.
AUX2-DO
The potential relay output can be freely used for liquid injection,
DE-SH or hot gas dumping.
Survey
Connection "572"
1. priority
MT3 x x
CRII x
Heat recovery x (x)
2. priority
Oil No
CRII
Fan error Max. 1 x x x
Alarm text Max. 1 x x x
Liquid
injection
DE superheat x x x
Hotgas dump x x x
DI3
"572"
"572"
DO3
x x x
HP DIHP DORec DIRec
DO6
x (x)
DO
AUX3-DI
This function shares an input with the heat recovery function.
AUX3-DI is possible only if heat recovery is not used.
AUX3-DI can then be used as an alarm input.
AUX3-DO
This function is reserved for heat recovery but only if a potential
relay output is also required to be activated when heat recovery is
regulated.
If the output is not used for heat recovery, it can be used for liquid
injection, DE-SH or hot gas dumping.
AUX_-DI as an alarm input
There are two alarm options:
• A "Fan error" that will be shown in the display and in the system
unit if it occurs.
• A text alarm that will be shown in the display and in the system
unit if it occurs.
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Safety functions
Control optimisation
The controller continually registers the different pressures in the
system.
The pressures are automatically adjusted for the most energyoptimal pressure.
If the pressure approaches a threshold value, the controller will
adjust the different references to maintain control.
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.
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
Pgc measurement exceeds the reference.
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 Pgc error, the fan 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, 35°C will be used as a reference.
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".
Fan error alarm
On/off signal on a DI input. Possible only if the input is not used
for its intended purpose.
If the signal is received, an alarm is given.
Min./max superheating via Ss and Po 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.
Max. discharge gas temperature Sd
Temperature sensor on an AI input.
There is an Sd for the MT group and an Sd for the LT group.
If the temperature nears the set max. temperature, the capacity of
the compressor will be reduced
The compressors will be stopped if the temperature nears
the set max. temperature value.
Liquid injection in the MT suction line
This function is configured in the AUX_DO output.
There are no configuration values. The controller determines when
liquid injection is required.
General DI alarm
On/off signal on a DI input. Possible only if the input is not used
for its intended purpose.
The controller contains one general alarm input, to which alarm
text and delay times can be connected.
Alarm and text will appear when the delay time has elapsed.
Info
In normal operating conditions, the temperature at Sd will be
between 60 and 70°C - depending on whether it is winter or
summer.
If the "Heat reclaim" function is to raise the condensing pressure,
the temperature may increase to 90° or higher.
The Sc3 sensor should be positioned so that it measures the air
intake temperature for the gas cooler. If it measures a temperature
that is too high, the system's COP will become impaired.
The Sgc signal must be stable. If this cannot be done using a surface sensor, it may be necessary to use an immersion tube sensor.
If the power supply to AK-PC 572 or the high pressure valve Vhp
fails, the system cannot be controlled. We recommend installing
an emergency supply (UPS) for both the controller and the valve
to avoid faults. A relay in the UPS should be incorporated into the
controllers safety circuit so that it can restart safely.
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Display overview
End-user overview
The images in this daily user interface will depend on how the set-up is made. They will illustrate what is regulated.
Click on the "Right Arrow" to view e.g. the following images:
Booster + HP
MT + HP
When an alarm is sent from the controller, you must advance to this
display to see the alarm text. Then
click on the alarm text to view the
details relating to the alarm.
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Set-up overview
There are 2 ways in which the controller can be set up. Select the one that is easiest for you: either “Wizard” or a review of
“all parameters”.
Start screen upon delivery
Operating principles
1. Select position using arrow keys
2. Select using “Enter”
3. Use the “X” to return
Hold “Enter” down
for 2 seconds to come to
password entry
Select a set-up method. End
by pressing “Enter”
The default password upon
delivery is 300. Use the arrow
keys to set the password. End
by pressing “Enter”
Language
Choose from one of the
possible languages
Wizard
Here you will be led through a series of settings, after
which the controller will be ready for start.
Image 1 of 27 is displayed here.
Parameter settings
Here is the start image for
the possible settings.
Main Menu
The first setting is the
Plant type
The following options are available here:
• Booster + HP
• MT + LT
When the Plant type has
been selected, it will allow several settings to be
made.
For example:
Continue to the next
menus.
All settings are explained
on the pages that follow.
AK-PC 572 User Guide RS8KH202 © Danfoss 2019-03 9
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