Fan Coil Actuator FCA 2
Updated: Feb-16 (subject to changes) Page
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6.9.2 Response of the P controller
Max. 4l/Min.
Bandwidth
Set point value
Actual value
17l
21l
15l
Losses
1l/Min
Figure 21
If the filling quantity is 15 l, there is a control deviation of 21 l – 15 l = 6 l
As our actual value lies outside the bandwidth, the control will operate the feed at 100 %,
i.e. with 4 l/minute.
The feed quantity (= actuating value) is calculated from the control deviation
(setpoint – actual value) und the bandwidth.
Actuating value = (control deviation / bandwidth) x 100
The following table illustrates the behaviour and also the limits of the P controller.
Table 71
Filling level
Actuating value Feed
Losses
Increase of filling
level
15 l
100 %
4 l/min
1 l/min
3 l/min
19 l
50 %
2 l/min
1 l/min
20 l
25 %
1 l/min
0 l/min
The last line shows that the filling level cannot be increased anymore, because the inlet feeds as
much water as can be discharged by the losses.
The result is a permanent control deviation of 1 l. The setpoint can never be achieved.
If the losses were increased by 1 l, the permanent control deviation would be increased by the
same amount, and the filling level would never exceed the 19 l mark.
In case of a room, this would mean that the control deviation increases with decreasing outdoor
temperature.
