Additional functions
51
Pump speed control
The pump speed control can be used to change the delivered quantity - i.e. the volume flow -
of usual commercial circulating pumps in 30 steps. This provides constant levels of (differen-
tial) temperatures in the system.
Setting of optional sensors and temperatures is possible. The pump speed control is – if acti-
vated – allowed, when the normal difference- and/or thermostat function enables the output,
i.e. it is like a device, which is connected after the normal controller.
This simple solar diagram will now be used to show the possibilities of this process:
Absolute value control A
= maintaining a sensor
T1
can be kept at one temperature (such as 60°C) very well by using the speed control. If
the solar radiation is reduced,
T1
becomes colder. The control unit then lowers the speed
and hence the flow rate. However, that causes the warm-up time of the heat transfer medium
in the collector to increase, thus increasing
T1
again.
A constant return (
T2
) may make sense as an alternative in various systems (such as boil-
er feeds).
Inverse
control characteristics are necessary for this (identified by a minus). If
T2
increases, the heat exchanger does not provide enough energy to the tank. The flow rate will
then be reduced. The longer dwell time in the exchanger cools the heat transfer medium
more, thus reducing
T2
.
It does not make sense to keep
T3
constant as the variation in the flow rate does not di-
rectly affect
T3
; hence, no regulator circuit will result.