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OPERATION
Appliance description
6 | WWK222-302 H www.stiebel-eltron.com
3. Appliance description
This appliance enables DHW to be supplied efficiently to several
draw-off points using renewable energy. The appliance extracts
heat from the ambient air. This heat is used to heat up the water
in the DHW cylinder with added electric power. The amount of
electrical energy and time required to heat up the hot water de-
pend on the temperature of the air drawn in and the temperature
of the water in the cylinder. When the air intake temperature
drops, the appliance heating output is reduced and the heat-up
time is extended.
Subject to the power supply and user draw-off behaviour, the
water is heated automatically to a temperature that is set at the
factory.
In the case of indoor installation, the air inside the installation
room can be cooled by 1°C to 3°C due to heat extraction. The
appliance also extracts moisture from the air, which turns into
condensate. The condensate is removed from the appliance via
the condensate drain.
The heat pump drive unit is located in the upper section of the
appliance. The DHW cylinder is located in the lower section of the
appliance. To protect against corrosion, the DHW cylinder is coated
internally with special enamel and is additionally equipped with
a non-sacrificial impressed current anode.
3.1 Heat pump operating principle
A closed circuit within the appliance contains refrigerant (see
"Specification/ Data table"). This refrigerant evaporates at low
temperatures. In the evaporator, which extracts heat from the
air drawn in, the refrigerant changes from a liquid into a gas-
eous state. A compressor draws in the gaseous refrigerant and
compresses it. This increase in pressure raises the refrigerant
temperature. That requires electrical energy.
The energy (motor heat) is not lost, but reaches the downstream
condenser together with the compressed refrigerant. There, the
refrigerant transfers heat to the DHW cylinder. An expansion valve
then reduces the still prevalent pressure and the cyclical process
starts again.
3.2 DHW heating
2
1
D0000050335
1 Cylinder top sensor
2 Integral sensor
The appliance is equipped with two temperature sensors.
- The cylinder top sensor captures the water temperature in
the upper section of the cylinder.
- The integral sensor is a temperature sensor affixed all the
way down the cylinder. The integral sensor determines the
average cylinder temperature.
The appliance control unit uses the average cylinder temperature
captured by the integral sensor. DHW heating is started when the
average cylinder temperature falls below the set temperature.
DHW is normally heated by the heat pump of the appliance (see
chapter "Specification/ Data table").
Note
If the appliance has been isolated from the power supply
during operation, the compressor will only restart after
the pressure inside the refrigerant circuit has been equal-
ised. Pressure compensation can take several minutes.
WWK222H|WWK302H: Electric emergency/booster heater
When the temperature in the upper section of the DHW cylinder
drops 10K below the selected set temperature, the appliance
automatically switches on the electric emergency/booster heater.
When the temperature in the upper section of the DHW cylinder
rises 2K above the selected set temperature, the appliance switch-
es off the electric emergency/booster heater.
3.3 Appliance operation outside the application
limits
3.3.1 Ambient temperatures below the application limit
Outside the application limits, the appliance blocks the compres-
sor from operating. This could lead to reduced DHW convenience.
If the appliance has an electric emergency/booster heater, this will
be enabled if a demand for heating up the water exists and the
lower application limit is underrun.
Low ambient temperatures may result in the formation of hoar
frost on the evaporator depending on the air humidity and water
temperature.
Active defrost feature
The appliance is equipped with active hot gas defrosting, which
allows quick defrosting of the evaporator when needed. During
defrosting, the appliance fan is deactivated. The compressor con-
tinues to run. A solenoid valve routes the hot gas directly to the
evaporator. While this is happening, refrigerant flow to the con-
denser is disabled by another solenoid valve.
In contrast to conventional defrosting methods, the appliance
guarantees that defrosting takes place only when needed.
Note
Heat-up times are longer while the evaporator is defrost-
ing.
3.3.2 Ambient temperatures above the application limit
Outside the application limits, the appliance blocks the compres-
sor from operating.This could lead to reduced DHW convenience.
If the appliance has an electric emergency/booster heater, this
will be enabled if a demand for heating up the water exists and
the upper application limit has been exceeded.
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