Danfoss DHP-H Installation And Service Instructions Manual page 48

DEFR CURVE, defrosting curve for DHP-A, -AL
To start defrosting the outdoor unit for DHP-A, -AL, the control computer makes a calculation using the temperature of the brine return
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 brine return 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 -20. 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 -20 for DEFR CURVE -20. The value -20 for DEFR CURVE -20
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 -20°C. At this outdoor temperature, compressor operation is stopped and the addition takes over. It is
seldom that the value of OUTDOOR STOP needs to be changed, tests and operating cases have shown that -20°C operates very well as the
stop temperature. In the text and figures below the value -20°C has been used for OUTDOOR STOP.
The control computer shows the value for DEFR CURVE 0 and DEFR CURVE –20 by means of a graph in the display.
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 brine return is permitted to reach when a defrost must start at outdoor tempera-
ture 0°C.
In the corresponding way the value for DEFR CURVE -20 is the temperature that the brine return 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 (-20°C) is reduced by
between 1 and 8 degrees. This also determines how much lower the temperature for the brine return may be than -20°C in this case.
Adjustable value for DEFR CURVE -20 is
1°C to 8°C lower than OUTDOOR STOP
These three settings together create the defrosting curve and all three values have an effect on when defrosting will start, even if it is main-
ly DEFR CURVE 0 and DEFR CURVE -20 that is changed.
48
Temperature, input brine line
Set value for
DEFR CURVE -20
Figure 89: Graph that shows how the value for DEFR CURVE 0 can be set.
Temperature, input brine line
Figure 90: Graph that shows how the value for DEFR CURVE -20 can be set.
Adjustable interval for DEFR CURVE 0 is
a brine return between -5°C and -15°C
at 0°C outdoor temperature
Outdoor temperature
Set value for
DEFR CURVE 0
Outdoor temperature
Set value for OUTDOOR STOP, -20°C
VMBMA602