A.O. Smith AHD 290 - Manual (Page 59)

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2.1 Description
Use of hot tap water heat pump:
The heat pump is only intended to produce hot tap water for domestic use within
the specified temperature limits. The sanitary hot water heat pump is a complete
unit with a 285 litre hot water tank, extraction fans, heat pump and also equipped
with a complete electrical equipment and five models are equipped with a heating
coil.
Capacity:
The heat pump is capable of producing a hot water volume of app. 1000 Litres at
45°C. The actual volume depends on the supplied fresh water temperature, air
temperature and the pattern of use of hot water. The additional electrical heat-
ing element (1,5 kW) may be used to boost the capacity whenever needed. The
heat pump only uses app. 27% of the energy compared to a conventional electric
boiler.
Heat pump operation:
The control starts the compressor shortly after hot water has been tapped. The
compressor will run until the entire tank has been heated to the set temperature
again. Usually the heat pump can produce a sufficient amount of hot tap water
covering the needs of a common family.
Water heating:
When hot water is drawn off, the tank will be refilled with cold water at the bottom.
A sensor measures the temperature at the bottom of the tank and starts the com-
pressor if the temperature has fallen 5°C below the set temperature. The com-
pressor stops, when the water has been heated to the set temperature. While the
compressor operates, the fans run and circulate air through the cooling surface.
Fan operation:
The fan may be set to run continuously, when the compressor has stopped - by
selecting level 2 or level 3. This option may be chosen when the heat pump is
used as an extraction system in the residential wet rooms. If the input to T4 short
circuits, the control is forced to run at 3rd speed. This may be used in order to
achieve more extract in e.g. bathroom, while taking a shower. When breaking the
short circuit on the input pins to T4, the control will return to its previous step.
Defrosting:
When the temperature difference between the temperature upstream of the cool-
ing surface and the temperature of the cooling surface becomes too large (as
happens when ice is formed on the cooling surface), the unit goes into defrost
mode. The magnetic valve MA 4 opens and the supply air fan stops until the ice
has melted and the cooling surface has reached a temperature of app. 5°C. Then
the magnetic valve closes again and the supply air fan resumes operation.
2.2 Extra capacity
If a situation should occur where the heat pump is not capable of producing
enough hot tap water (more people in the house), an extra electrical
cartridge in the container can be switched on. Doing so, it is possible to heat up
more water. It is possible to set the desired temperature to which the
electrical cartridge should heat up the water. (Only use the electrical
cartridge when needed, as it uses more energy than the compressor).
The electrical cartridge can be activated manually on the display.
2. Function