AK-CC 550
Manual RS8EN502 © Danfoss 02-2010
7
Coordinated defrost
There are two ways in which coordinated defrost can be arranged.
Either with wire connections between the controllers or via data
communication
Wire connections
The digital input DI2 is connected between the current controllers.
When one controller starts a defrost all the other controllers will
follow suit and likewise start a defrost. After the defrost the indi
-
vidual controllers will move into waiting position. When all are in
waiting position there will be a change-over to refrigeration.
Coordination via data communication
Here the system unit handles the coordination.
The controllers are gathered in defrosting groups and the system
unit ensures that defrosting is started in the group according to a
weekly schedule.
When a controller has completed defrosting, it sends a message
to the system unit and then goes into a waiting position. When
every controller in the group is in a waiting position, refrigeration
is again permitted in all the individual controllers.
System manager
Defrost on demand
1 Based on refrigeration time
When the aggregate refrigeration time has passed a fixed time,
a defrost will be started.
2 Adaptive defrosting based on monitoring of evaporator per
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formance
This function is based on a registration of the air flow through
the evaporator. By using the AKV valve as mass flowmeter for the
refrigerant flow it is possible to compare the energy input on the
refrigerant side with the energy output on the air side. Via this
comparison the air flow through the evaporator can be deter
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mined and hence also the amount of ice/frost build-up on the
evaporator surface. If the ice/frost build-up reduces the capac
-
ity of the evaporator the function will carry out an additional
defrost.
Enter in the weekly defrost schedule the number of defrosts
corresponding to the basic load. If the load of the evaporator is
increased beyond this, defrost on demand will add the required
additional defrosts.
The function requires the following connections:
- Expansion valve type AKV
- Temperature signal from both S3 and S4
- Temperature signal from the condensing pressure Pc which is to
be distributed via the network from the system manager.
NOTE. The S3 and S4 sensors must be placed in the air flow/chan
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nel immediately before/after the evaporator.
Min. time between defrosts
There is a 2 hours minimum time between defrosts.
This avoids that planned defrosts in accordance with the weekly
schedule are carried out immediately after a defrost on demand
has been carried out. The time applies from when a defrost on
demand has been completed to when a planned defrost is again
permitted. The defrost on demand will not start defrosting with a
shorter interval than the 2 hours either.
Reset
If the adaptive defrost function registers problems with the
defrost, it will show an error message and the function will no
longer carry out extra defrosts. In this event a manual reset of the
function via d22 should be carried out.
When the reset function is activated it will start a defrost so that
the subsequent tuning will take place on an evaporator with no
ice/frost build-up.
Note
The function "Adaptive defrost” should only be activated when the
evaporator runs under normal operational conditions.
Melting function
This function will stop the air flow in the evaporator from being re
-
duced by frost created by uninterrupted operation for a long time.
The function is activated if the thermostat temperature has
remained in the range between -5°C and +10°C for a longer
period than the set melting interval. The refrigeration will then be
stopped during the set melting period. The frost will be melted
so that the air flow and hence the evaporator’s capacity will be
greatly improved.
Real-time clock
The controller has a built-in real-time clock which can be used to
start defrosts. This clock has a power reserve of four hours.
If the controller is equipped with data communication, the clock
will automatically be updated from the system unit.
Max. 10