Installation manual
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Integration of the Heat Pump in the Heating System 8.7.3
8.5.5 Check valve
If a water circuit contains more than one circulating pump, each
pump unit must be equipped with a check valve to prevent mixing
from other heating circuits. It should be ensured that check
valves close tightly and are noiseless during flow through.
NOTE
Dirt particles can prevent the valves from fully closing. This could, for
example, lead to insufficient domestic hot water temperatures and
swimming pool temperatures if cold heating water is added during
domestic hot water preparation and swimming pool heating.
8.6 Flow Temperature Limit of Underfloor Heating
Many underfloor heating pipes and screed floorings should not
be heated over 55 °C. In the case of bivalent operation or if the
buffer tank is charged externally, a limitation of the flow
temperature must be effected to prevent such overheating.
NOTE
With a mixer in the underfloor heating circuit or in bivalent-renewable
operating mode, the mixer is closed when the temperatures are too high.
A safety temperature monitor prevents increased system temperatures
due to mixer sluggishness or failure.
8.6.1 Flow temperature limiting via a mixer limit switch
The mixer is only opened so wide at full boiler output and
maximum boiler temperature that the maximum flow temperature
of approx. 55 °C is not exceeded. A further mixer open
command is prevented by locking the freely controllable mixer
limit switch in this position.
We recommend installing a mixer motor equipped with a limit
switch so that the drive can be switched off electrically.
8.6.2 Flow temperature limiting using mixer bypass
At full boiler output, maximum boiler temperature and with the
mixer opened completely, the bypass is opened so wide that the
maximum flow temperature is not exceeded. This limits the flow
temperature. The regulator valve must be secured against
accidental adjustment.
We recommend using mixers equipped with an internal bypass.
This type of flow temperature limiting is particularly suitable for
underfloor heating.
Fig. 8.14: Bypass circuit for safeguarding the maximum flow temperature
8.7 Mixer
The mixer is in the “closed” position (for the boiler) in heat pump
only operation and directs the hot flow water past the boiler. This
prevents downtime losses. The mixer is dimensioned according
to the boiler output and the flow rate volume.
The mixer drive must have a runtime of between 1 and 6
minutes. The heat pump manager controls the mixer and can be
set to this runtime. We recommend using mixers with a runtime
of between 2 and 4 minutes.
8.7.1 Four-way mixer
The four-way mixer is generally required for oil boilers with fixed
temperature regulation. These may not be operated below
temperatures of 70 °C (poss. 60 °C). The four-way mixer mixes
the boiler temperature to match the currently required flow
temperature. Using the effect of an injector, the four-way mixer
maintains a circulation in the boiler circuit which flows in the
opposite direction of the heating system circuit. This ensures that
the heating water returning to the boiler is always hot enough to
prevent the dew point in the boiler from being undershot (which
in turn would cause the return flow temperature to rise).
8.7.2 Three-way mixer
The three-way mixer is used to regulate individual heating
circuits and is also implemented when low-temperature boilers or
condensing boilers with burner regulation are used (e.g.
“variably-regulated boilers”). These types of boilers can have
cold return flow water circulating through them. The three-way
mixer thus serves as a kind of switching valve. It is completely
closed in heat pump only operation (prevents downtime losses)
and is completely open in boiler operation.
8.7.3 Three-way solenoid valve (switching valve)
Three-way solenoid valves are not to be recommended for this
application because they do not function reliably and can
transmit sound to the heating system.
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