Components - Danfoss DHP-AX Installation And Service Instructions Manual

11.2.2 Defrost function
During operation the air heat exchanger is cooled by the energy exchange at the same time as the humid-
ity causes it to become covered in frost. DHP-AX has an automatic function to defrost the air heat exchanger
using the produced heat energy. If necessary, a defrosting sequence starts which means the following:
T he defrost sequence starts when the temperature of the incoming refrigerant is lower than the set value,
z z z z
which is based on a curve that is related to the outdoor temperature
T here are restrictions for the defrost regarding time in operation and FAN on
z z z z
T he four way valve in the heat pump switches the direction of flow of the refrigerant and the fan stops, see
z z z z
figure below
T he hot refrigerant melts the frost on the air heat exchanger
z z z z
D efrost stops on time, operating pressostat or incoming temperature
z z z z
T he four way valve switches the direction of flow of the refrigerant back so that heat production resumes
z z z z
and operation returns to normal
Low pressure
Refrigerant sensor 1
The figure above shows DHP-AX during defrost. The process is reversed by means of the four way valve that
changes the direction of flow, which means that the air heat exchanger for heating becomes a condenser and
the heating's condenser becomes an evaporator. This function is used for defrosting.
As the heat pump's defrosting sequence retrieves its energy from the house's heated heating system during
the winter months, the water tank is primarily used as a heating buffer. If a water heater is not installed, the
water volume in the heating system must be increased, if the volume does not meet the demand, by installing
a surge tank (accessory).
11.3

Components

The heat pump is a complete heat pump installation for heating and hot water.
The heat pump is equipped with control equipment, which is controlled via a control panel.
Heat enters the house via a water borne heating system. The heat pump supplies as much of the heat demand
as possible before auxiliary heating is engaged and assists.
Pressostat Service output
Bulb
Compr.
Fan
Refrigerant sensor 2
Figure 17: The refrigerant circuit's function during defrost.
Pressure pipe Pressostat
sensor High pressure
4-way valve in
defrost mode
2-way
Drying filter
exp.valve
VMBMH302
Hot
Cold
Refrigerant sensor 3
Heating system
cold supply
Heating system
hot return
Service – 23