Danfoss DHP-A User Manual page 9

from the outside air. During operation the coil is cooled by the energy
exchange at the same time as the humidity causes it to become covered
in frost. DHP-A has an automatic function to defrost the coil using the
produced heat energy. If necessary, a defrosting sequence starts which
means the following:
•
The defrosting sequence starts when the temperature of the brine
reaches its set parameter for defrosting.
•
The compressor is stopped so that the defrosting sequence should
not load the compressor unnecessarily. But the compressor is not
stopped when it produces hot water because the water heater is
cooled when defrosting. The fan on the outdoor unit is stopped in
conjunction with defrosting to shorten the time of defrosting.
•
The shunt valve in the heat pump opens so that hot brine from the
defrosting tank is mixed with the cold brine circulating to the out-
door unit. The mixture has a temperature of about 15°C.
•
The fifteen degree heated brine melts the frost on the outside of the
coil at the same time as the liquid is cooled.
•
When the brine is no longer cooled to temperatures below 11°C the
coil is sufficiently defrosted.
•
The shunt valve closes the flow of hot brine from the defrosting
tank.
•
Operation returns to normal.
Speed (rpm) control
Applies to certain heat pump models.
A heat pump requires optimum conditions in the heating system and
brine circuit in order to be able to run as efficiently as possible. The tem-
perature difference between the heating system's supply line and
return line must be constant between 7–10°C. For the brine circuit a
temperature difference of 3°C between input and output line applies. If
the differences are greater or less, the heat pump is less efficient and
savings are lower.
A heat pump with speed controlled circulation pumps always ensures
that they retain the temperature differences. The control equipment
detects if the balance is upset and increases or decreases the speed of
the circulation pumps as necessary.
HGW technology
User manual VUBMA902 – 7