Additional functions
52
Differential control F
= keeps the temperature constant between two sensors.
Keeping the temperature difference constant between
T1
and
T2
, for instance, allows for
“shifting” operation of the collector. If
T1
drops due to lower irradiation, the difference be-
tween
T1
and
T2
thus drops. The control unit then lowers the speed, which increases the
dwell time of the medium in the collector and hence the difference between
T1
and
T2
.
An inversely written
F
means an inverse speed characteristic, i.e. the speed increases with
falling difference.
Note
: This difference “
d
” always has to be greater than the switch-off difference
diff
of the
basic function. If „
d
“ is lower, the basic function of pump release blocks before the speed
control has reached the desired value.
Limiter function L
= If a set temperature event occurs, the speed control starts, thus
keeping a sensor constant.
If, for instance,
T3
reaches 55°C (activation threshold), the collector should be kept at a
certain temperature. Maintaining a sensor then works as with absolute value control. An in-
versely written
L
means an inverse speed characteristic, i.e. the speed increases with falling
temperature.
The three described methods can be activated all together. If the absolute value control
(maintaining a sensor) and the differential control (maintaining the difference between two
sensors) are both active, the slower of the two speeds “wins out”. The limiter function “over-
writes” the speed results from other control methods. A set limit can thus block the control of
absolute values or differences.
In the example, keeping the collector temperature at 60°C with the absolute value control is
blocked when the tank has already reached 55°C at the top = the fast provision of hot water
is complete and is now to be continued with full volume flow (and hence a lower temperature
but slightly better efficiency). To do so, a value that value automatically requires full speed
(such as S1 = 10°C) has to be entered as the new desired temperature in the event control.
Waveform
Wave packets
- only for circulating pumps with standard motor dimensions. Here, individual
half cycles are bled in to the pump motor. The pump runs on pulses and only produces a
smooth flow of the heat transfer medium when the rotor’s moment of inertia has been over-
come.
Benefit:
Great dynamics of 1:10, well suited for usual commercial pumps without internal
electronics and a motor length of around 8 cm.
Drawback:
Linearity depends on the pressure loss; there is some noise, not suitable for
pumps with evidently deviating motor diameters and / or length from 8 cm.