Defrost - Danfoss AK-CC 750A User Manual

Defrost

There is a common defrost start for all evaporator sections. Defrost
stop can be common or individual when based on temperature.
Refrigeration will not be re-started until defrost has been accom-
plished in all sections.
Fan control during defrost
Choose whether the fans should be running or stopped during the
defrost sequence.
Coordinated defrost
If there are several controllers that are to perform defrost at the
same time they can be grouped from the system unit. The system
unit will start the defrosts, and when the defrost of the individual
controllers is later finished they will go into "stand-by" position
until all the defrosts have been terminated. Refrigeration is then
resumed.
Drip tray heating element
It is possible to control a heating element in the drip tray for hot
gas defrost. When defrost is commenced, the heating element is
activated. The heating element remains activated until a set time
after defrost has ended by time or temperature.
Defrost type
Electric defrost
When there is electric defrost, the individual sections' heating ele-
ments are controlled separately.
Natural defrost
Defrost is accomplished here by the fans circulating air through
the evaporator.
Warm brine defrost
Warm brine defrost can be used on indirect refrigeration systems
with solenoid valves. During warm brine defrost, the solenoid
valve is kept open during defrost so that the warm brine can run
through the "evaporator".
AK-CC 750A RS8HP102 © Danfoss 2018-09
Hot gas defrost
During hot gas defrost, the controller regulates valves in the liquid
line, hot gas valves, a suction line valve and a drain valve.
A time delay can be set which defers opening of the hot gas valve.
Defrost start
Defrost can be started in several ways. Once started it will continue
until a "defrost stop" signal is received.
- Manual defrost
Manual defrost can be enabled via a setting in the controller or
via the bottom button on the display.
After activation the setting moves back to position OFF when the
defrost has been completed.
- External signal on input
Defrost start is done with a signal on a DI input. The signal must
be an impulse signal of at least three seconds' duration. Defrost
starts when the signal moves from OFF to ON.
- Schedule – weekly programme
Defrost can be started via an internal schedule or via an external
schedule placed in the network's system unit.
• Internal schedule
Defrost is started by means of a weekly programme that is set
in the controller. The times have relation to the controller's
clock function. Up to eight defrosts per 24 hours can be set. The
schedule can be found via the "Overview display" / "Defrost" /
"Schedule".
• External schedule
Defrost is started via a signal from the network's system unit
- Interval
Defrost starts with set intervals, e.g. every eight hours. An inter-
val must ALWAYS be set to a "higher" value than the period set
between two defrosts when a schedule or network signal is used.
Defrost according to intervals ensures that defrost always takes
place, even if no signal is received from the network's system
unit.
- Adaptive defrost
This function can cancel planned defrosts which are not neces-
sary, and on its own initiative it can start a defrost if the evapora-
tor is about to be blocked by rime and ice.
(The "Adaptive defrost" function is described at the end of the
section.)
Defrost sequence
Every defrost runs through the following sequence:
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