134
Drain-Back
This additional function can only be activated with programs for one collector field and one
consumer (e.g. programs 0, 80, 112, 432 etc.) or program 4.
With drain-back solar thermal systems the collector area is emptied outside the circulation
time. In the simplest case, a solar pump is accordingly installed close to an open expansion
cylinder, which when the pump is stationary receives all the heat transfer medium above the
cylinder.
System start up is triggered either by a radiation sensor or by the exceeding of the tempera
-
ture difference
diff
On
between the
collector-
and
cylinder sensor
.
During the filling time the pump runs at full speed to lift the heat transfer medium above the
highest point of the system. Optionally, a second pump („booster pump“) can be connected
to a free output, so that the filling pressure is increased.
Filling of the collector with cold heat transfer medium leads to the short-term undershooting
of the switching difference diff
diff
Off
. In the following stabilization time the pump continues
to run irrespective of the temperature difference
diff
Off
at the
calculated speed.
If the pump is switched off during normal operation (e.g. as a result of undershooting of the
temperature difference
diff
Off
or collector overtemperature switch-off), then the heat trans
-
fer medium runs out of the collector field back to the expansion cylinder.
A volume flow sensor is suitable for use as low water protection (VSG... or FTS...DL). If the
volume flow falls below a minimum value after the stabilization time, the solar pump is
switched off and the error message
Drain-back Err.
appears in the status menu. The system
can only restart after the error has been dismissed.
For the speed control of the pump, a
control output
(for pumps with internal electronics with
0-10V or PWM input) must be activated. It makes sense to define a minimum speed for the
stabilization time, that safeguards the circulation.
If an
electronic pump with 0-10V or PWM input
is used as booster pump during the filling
time,
control output 2
must be activated and assigned to the output of the booster pump.
The analogue level for full speed is output during the filling time.
The
start function
must
not
be used alongside the drainback function. If the drainback func
-
tion is activated, the frost protection should not the be activated alongside it (with the excep
-
tion of program 4)
Summary of Contents for UVR65
Page 2: ......
