Heat Pump Operating Principle; Dhw Heating - STIEBEL ELTRON WWK 221 electronic Bedienung Und Installation

oPerATIoN
Appliance description
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 gaseous state. A com-
pressor draws in the gaseous refrigerant and compresses it. This
increase in pressure raises the refrigerant temperature. This re-
quires electrical energy. The energy (motor heat) is not lost, but
reaches the downstream condenser together with the compressed
refrigerant. There, the refrigerant indirectly transfers heat to the
DHW cylinder. An expansion valve then reduces the still prevalent
pressure and the cycle starts again.
If a compressor is required, the appliance does not start the
compressor immediately; only once the fan's initial runtime has
elapsed. During the fan's initial runtime the appliance checks if all
the conditions required to start the compressor have been met.
Note
Following an interruption to the power supply, compres-
sor operation remains blocked for at least one minute.
The PCB delays the electrical start-up by one minute,
during which the appliance initialises.
If the compressor subsequently fails to start, it may be
locked out by additional safety devices (motor overload
relay and high pressure switch). This block should lift
after 1 to 10 minutes.
After the power supply has been re-established, the ap-
pliance continues to operate with the parameters that
were selected before the power supply was interrupted.
3.2

DHW heating

1
2
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 over the
entire cylinder height. The integral sensor determines the
average cylinder temperature.
The appliance display indicates the temperature in the upper sec-
tion of the cylinder, which is captured by the cylinder top sensor.
The appliance control unit uses the average cylinder temperature
captured by the integral sensor.
DHW heating is started when the available mixed water volume
decreases to the percentage of the maximum mixed water volume
set in the "Charge level" parameter.
The temperature captured by the cylinder top sensor may still
correspond to the set temperature.
46 | WWK 221-301 electronic
For information on the heat-up time, see chapter "Specification".
The calculation of the available mixed water volume is based on
the average cylinder temperature. The amount of mixed water is
only calculated if the water temperature in the upper section of
the cylinder is higher than 40 °C.
DHW is normally heated by the heat pump of the appliance within
the application limits (see chapter "Specification / Data table").
Electric emergency/booster heater
Heat pump operation will be interrupted if the application lim-
its are exceeded or undershot in heat pump mode. The electric
emergency/booster heater takes over DHW heating to the selected
set temperature. Once the appliance is back within the application
limits, the electric emergency/booster heater switches off and
DHW heating continues with the heat pump.
In the event of an appliance fault, the electric emergency/booster
heater can be activated in emergency mode if the symbol "service/
fault" is flashing. See chapter "Settings / 'Rapid heat-up' button /
Emergency heating mode".
In the event of a higher hot water demand on a single occasion,
use the "Rapid heat-up" button to activate the emergency/booster
heater manually for one-off heat-up in addition to the heat pump.
See chapter "Settings / 'Rapid heat-up' button / Rapid/comfort
heat-up".
Set temperature adjustment subject to air temperature
If the temperature of the intake air is low, the maximum hot gas
temperature may be reached. In this case the appliance reduces
the set temperature on a temporary basis. Whilst the appliance
is operating at a reduced set temperature, the symbol for set
temperature adjustment is shown in the display.
Runtime-dependent rapid heat-up
The appliance offers runtime-dependent rapid heat-up for im-
proved comfort. When this function is enabled, and the adjusted
set temperature is not reached by the heat pump after a user-de-
fined period, the appliance switches on the electric emergency/
booster heater in parallel. This function is disabled at the factory.
When the air intake temperature drops, the heat pump's heating
output is reduced and the heat-up time is extended. In the case
of installation with outdoor air intake, we recommend enabling
"runtime-dependent rapid heat-up" during the winter months and
as required in spring/autumn when outside temperatures are low.
Note that DHW heating with the electric emergency/booster heater
uses more power than just using the heat pump.
To prevent excessive power consumption, disable the function in
summer and in spring/autumn if possible. When the function is
activated, we recommend only reducing the factory preset of 8
hours if absolutely necessary for the same reason.
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