eta TWIN 20 kW, Operation

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ETAtouch controller [Solar] function block
69
In solar heating systems with external heat
exchangers, experience has shown that most of the
energy from the solar heating system goes to the tank
in this control principle. 9.8.5 Solar heating system with external
heat exchanger and stratified
charging valve
Solar heating system with external heat exchanger
and stratified charging valve
This variation of solar heating system also aims to
produce a sufficiently high temperature in the upper
area of the buffer, so the boiler does not have to start
for hot water charging.
Fig. 9-62: Solar heating system with external heat exchanger
and stratified charging valve
The collector pump starts as soon as the collector is
warmer than the target temperature in the upper buffer
area [Buffer target solar].
The control principle is identical to that of a buffer with
two internal coils. The conditions for solar charging into
the upper buffer coil are also the same. They are
described in chapter
9.8.3 "Solar heating system for
buffer with 2 internal coils" .
The speed control of the secondary pump is identical
to that of a solar heating system with an external heat
exchanger, see chapter
Fig. 9-61: "Regulation
principle" .
The only difference is the switching of solar
charging from the lower buffer coil to the upper. If
the conditions for solar charging into the upper coil are
not met, the lower coil will be charged first. If the
secondary feed temperature rises enough that the
temperature in the upper buffer area [Buffer top Solar]
is exceeded, solar charging is immediately switched to
the upper coil. There is no minimum time for solar
charging. Once the secondary feed temperature drops
below the temperature [Buffer top Solar], the lower coil
is again charged.
The secondary flow temperature rises when the
collector temperature increases or the speed of
the secondary pump decreases.