Control conditions
Control conditions defrosting
■
Defrosting occurs actively (with compressor on and
fan off) or passively (with compressor off and fan on).
■
A time counter counts up every minute if the com-
pressor is running and the temperature of the evap-
orator sensor (BT16) falls below a threshold value.
■
Time until defrosting in minutes appears on the in-
door module/control module. Defrosting starts when
this value is 0 minutes.
■
If "de-icing fan" is activated in menu 5.11.1.1, fan de-
icing starts during defrosting. De-icing fan prevents
the build-up of ice on the fan blades and the front
fan grille.
■
If the evaporator is too cold, a "safety defrost" starts.
This defrosting can be started earlier than when the
normal defrosting would start. If 10 safety defrosts
in a row occur, an alarm 341 is activated which is a
permanent alarm.
■
If defrosting is necessary, passive defrosting starts if
temperature sensor BT28 is greater than 4 °C and
the compressor has stopped because the heating
requirement has been met.
Active defrosting:
1.
The four way valve shifts to defrosting.
2.
The fan stops and the compressor continues to run.
3.
When defrosting is complete, the four-way valve
switches back to heating operation. The com-
pressor speed is locked for a short period.
4.
The ambient temperature sensor is locked and the
high return temperature alarm is blocked for two
minutes after defrosting.
Passive defrosting:
1.
The compressor stops.
2.
The four way valve does not shift.
3.
Fan runs at high speed.
4.
When passive defrosting is complete, the fan stops.
5.
The ambient temperature sensor is locked and the
high return temperature alarm is blocked for two
minutes after defrosting.
6.
If there is a heat demand, passive defrosting stops
and the compressor starts.
There are several possible reasons for an active
defrosting to end:
1.
If the temperature of the evaporator sensor has
reached its stop value (normal stop).
2.
When defrosting has gone on for longer than 15
minutes. This may be due to too little energy in the
heat source, too strong a wind effect on the evap-
orator and/or that the sensor on the evaporator is
not correct and therefore displays too low a tem-
perature (at cold outdoor air).
3.
When the temperature on the return line sensor
channel BT3 falls below 10 °C.
4.
If the temperature of the evaporator (BP8) falls
below its lowest permitted value. After ten failed
defrosts, an alarm occurs: 228.
NIBE™ F2120Chapter 7 | Control - Introduction34
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