Danfoss DHP-AX Installation And Service Instructions Manual page 28

11.5.9 DEFR CURVE
To start defrosting the outdoor unit, the control system makes a calculation using the temperature of the incoming refrig-
erant and the outdoor temperature.
What guides the calculation is a linear defrosting curve that can be set so that the heat pump and outdoor unit work
optimally. The setting of three different values can be changed: DEFR CURVE 0 , DEFR CURVE –20 and OUTDOOR STOP.
The defrosting sequence starts when the temperature of the incoming refrigerant reaches the set parameter value at an
outdoor temperature somewhere along the set defrosting curve.
The two parameters that are mainly changed are DEFR CURVE 0 and DEFR CURVE -16. The numbers behind the DEFR
CURVE display what outdoor temperature the setting is for, that is to say at 0°C for DEFR CURVE 0 and -16 for DEFR CURVE
-16. The value -16 for DEFR CURVE -16 is the set value for OUTDOOR STOP, so if the value for OUTDOOR STOP changes, the
numbers behind DEFR CURVE also change.
Factory setting for OUTDOOR STOP is -16°C. At this outdoor temperature, compressor operation is stopped and the addi-
tion takes over. It is seldom that the value of OUTDOOR STOP needs to be changed, tests and operating cases have shown
that -16°C operates very well as the stop temperature. In the text and figures below the value -16°C has been used for
OUTDOOR STOP.
The display shows the value for DEFR CURVE 0 and DEFR CURVE –16 by means of a graph in the character window.
The value for OUTDOOR STOP that is set means that the compressor will no longer be used for heating or hot
water production if the outdoor temperature is the same as or lower than the value. Heating and hot water
production then occurs with the help of the auxiliary heater.
The value for DEFR CURVE 0 is the temperature that the incoming refrigerant is permitted to reach when a
defrost must start at an outdoor temperature of 0°C.
In the corresponding way the value for DEFR CURVE -16 is the temperature that the incoming refrigerant has
when a defrost should start at the set outdoor temperature for OUTDOOR STOP. The setting for DEFR CURVE
–20 means that the value OUTDOOR STOP (-16°C) is reduced by between 1 and 5 degrees. This also determines
how much lower the temperature for the incoming refrigerant may be than -16°C in this case.
Adjustable value for DEFR
CURVE -16 is -1°C to -5°C lower
than OUTDOOR STOP
These three settings together create the defrosting curve and all three values have an effect on when defrost-
ing will start, even if it is mainly DEFR CURVE 0 and DEFR CURVE -16 that is changed.
28 – Service
Temperature, input refrigerant line
-10
Set value for
DEFR CURVE -16
Figure 25: Graph that shows how the value for DEFR CURVE 0 can be set.
Temperature, input refrigerant line
-10
Figure 26: Graph that shows how the value for DEFR CURVE -16 can be set.
-10
Set value for
DEFR CURVE 0
-10
Outdoor temperature
Set value for OUTDOOR STOP, -16°C
VMBMH302
Adjustable interval for DEFR CURVE 0 is
a brine return between -5°C and -15°C
at 0°C outdoor temperature
Outdoor temperature