Coordinated Defrost; Adaptive Defrosting; Coordination Via Data Communication; Min. Time Between Defrosts - Danfoss AK-CC55 User Manual

User Guide | Controller for appliance control, AK-CC55

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 must be configured for coordinated defrost
and wiring must be connected between the relevant controllers.
When one controller starts a defrost, all the other controllers
will follow suit and likewise start a defrost. After the defrost the
individual 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 manager handles the coordination.
The controllers are gathered in defrosting groups and the system
manager 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.

Adaptive defrosting

The Danfoss adaptive defrost algorithm detects the amount of
ice build-up and cancels a scheduled defrost, or it can be set
up to only perform defrost if the evaporator air flow is getting
interrupted by frost or ice.
The overall concept is based on comparison of the energy uptake
on the refrigerant flow side with the energy emission on the air
flow side. When the evaporator is clean an energy balance is
assumed, while a growing imbalance can be identified when ice
formation is build up on the evaporator surface ending up with
blocked airflow.
4 different adaptive defrost modes are available:
0 Off
1. Monitoring:
Can be set up in parallel to other defrost methods and generate an
alarm in case of blocked air flow / ice-up of the evaporator. If flash
gas issues are detected on the refrigerant flow side, a flash gas
alarm is generated.
2. Adaptive skip day:
Allows the controller to cancel (skip) defrosts scheduled within day
time. Defrosts scheduled at night operation will be carried through
and not skipped. Only defrosts that are set up via a schedule in the
frontend using master control functions or set up via the internal
defrost schedule in the controller can be skipped.
3. Adaptive skip day and night:
With this set-up, the controller can allow to cancel (skip) defrosts
scheduled both within day time and within night time.
For safety reasons max. 3 consecutive defrosts can be skipped,
where after the 4th scheduled defrost will be performed even if
only little ice should be present.
4 Full adaptive:
Full Adaptive mode is ideal for applications where defrost is not
requested to be performed at a certain time, but can be performed
whenever ice is starting to interrupt the airflow. It makes sense
to combine this mode with the defrost interval timer as a safety
timer.
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System manager
Adaptive defrosting requires the following connections:
- Expansion valve type AKV
- Pe evaporator pressure and S2 gas out temperature
- Temperature signal from both S3 and S4. Sensors must be
placed in the airflow/channel immediately before / after the
evaporator.
- Condensing pressure Pc and temperature Tc is distributed
via the network from the system manager. If Pc and Tc is not
received by the case controller, the adaptive defrost function is
disabled.
Note:
Adaptive parameters will be reset after a defrost has been initiated
or at main switch in stopped or service mode. At start up with a
warm evaporator (measured with S2 sensor), the evaporator is
presumed clean. If the evaporator temperature is measured below
0.1 °C, adaptive defrost will request a defrost start to secure a clean
evaporator.

Min. time between defrosts

There is a preset 2 hours minimum time between defrosts.
This avoids that planned defrosts in accordance with the weekly
schedule are carried out immediately after an adaptive defrost has
been carried out. The time applies from when an adaptive defrost
has been completed to when a planned defrost is again permitted.
The adaptive defrost will not start defrosting with a shorter
interval than the 2 hours either.
Max. 10.
© Danfoss | DCS (vt) | 2019.09