Heating And Defrost Functions - Danfoss DHP-AX User Manual

2.3

Heating and defrost functions

2.3.1 Heating
DHP-AX is a heat pump that produces heating for houses and water heaters
depending on the existing demand. Hot water production is continuous but during
the summer heat production to the house is stopped when the outdoor tempera-
ture reaches the value for HEAT STOP.
During the winter, hot water and heat is produced for the house by the compres-
sor until the outdoor temperature reaches the value for OUTDOOR STOP when it
becomes too cold for the compressor to operate. If an auxiliary heater has been
installed, it is used to produce hot water and heating for as long as OUTDOOR STOP
applies.
DHP-AX defrosts the air heat exchanger automatically if required.
2.3.2 Defrost function
During operation the air heat exchanger is cooled by the energy exchange at the
same time as the humidity causes it to become covered in frost. DHP-AX has an
automatic function to defrost the air heat exchanger using the produced heat ener-
gy. If necessary, a defrosting sequence starts which means the following:
The defrost sequence starts when the temperature of the incoming refrigerant is
z
lower than the set value, which is based on a curve that is related to the outdoor
temperature
There are restrictions for the defrost regarding time in operation and FAN on
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The four way valve in the heat pump switches the direction of flow of the refrig-
z
erant and the fan stops, see figure below
The hot refrigerant melts the frost on the air heat exchanger
z
Defrost stops on time, operating pressostat or incoming temperature.
z
The four way valve switches the direction of flow of the refrigerant back so that
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heat production resumes and operation returns to normal
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 by installing a surge tank (accessory).
VUBMI102
DHP-AX – 9