97
Absolute value control
= maintaining a sensor
S1 can be kept at one temperature (such as 50°C) very well by using the speed control. If
the solar radiation is reduced, S1 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 S1 again.
A constant return (S2) may make sense as an alternative in various systems (such as
boiler feeds). Inverse control characteristics are necessary for this. If S2 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
S2. It does not make sense to keep S3 constant as the variation in the flow rate does not
directly affect S3; hence, no regulator circuit will result.
The absolute control is set via two parameter windows. The
example
has typical settings
for the hydraulics:
AC N 1
A
bsolute value
c
ontrol in
n
ormal operation, with sensor S
1
being kept
constant.
Normal
operation
N
means that the speed increases as temperatures do and
is valid for all applications to keep a “feed sensor” constant (collector, boiler,
etc.)
Inverse
operation
I
means that the speed decreases as temperatures drop
and is necessary to maintain a return or control the temperature of a heat
exchange outlet via a primary circulating pump (such as hygienic hot water). If
the temperature at the heat exchanger’s outlet is too high, too much energy
yield enters the heat exchanger, thus reducing the speed and hence the input.
(ex works = --)
Setting range:
AC N 1 to AC N6, AC I 1 to AC I 6
AC -- = absolute value control is disabled.
DVA 50
The
d
esired
v
alue for
a
bsolute value control is
50
°C. In the example, S1 is
thus kept at 50°C. (ex works = 50°C)
Setting range:
0 to 99°C in increments of 1°C
