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Building Technologies
Modular Heating Controller RMH760B
CE1P3133en
HVAC Products
10 DHW heating
05.02.2007
Operating line
Range
Factory setting
Actuator running time closing
1…600 s
15 s
P-band Xp at min load
1…200 K
100 K
P-band Xp at max load
1…200 K
33 K
Integr action time Tn at min load
0…600 s
30 s
Integr act time Tn at max load
0…600 s
6 s
Deriv act time Tv at min load
0…255 s
8 s
Deriv act time Tv at max load
0…255 s
2 s
10.5.1 Adapting the control parameters
Among other things, the characteristics of the controlled system are affected by the
current DHW consumption and the connection conditions on the primary side.
For the different types of plant, the connection conditions on the primary side can
change depending on the time of year.
In the winter, the primary line operates at 6 bar and 120 °C, but in the summer only at
2 bar and 90 °C. This means:
In order to convey constant amounts of energy, the primary valve’s stroke in the sum-
mer must be different from that in the winter.
The controller acquires these changes and constantly adjusts the control action.
The velocity of flow on the secondary side has a great impact on the control character-
istics. Since this shall not lead to any disadvantages for the user in the case of direct
DHW heating, additional setting choices have been made available. These are the
following setting parameters:
•
The P-band for the minimum load
•
The integral action time for the minimum load
•
The derivative action time for the minimum load
•
The P-band for the maximum load
•
The integral action time for the maximum load
•
The derivative action time for the maximum load
This means that changing connection conditions need not be considered since the
controller makes automatic readjustments.
For DHW control, the actuator running time must be set. When using asymmetric
actuators, the actuator running times for opening and closing can be individually set. In
the case of symmetric actuators, the actuator running times to be entered for opening
and closing are the same.
It is important to also set the actuator running times when using DC 0…10 V actuators.
Only these settings ensure correct functioning of the control system.
The proportional band influences the controller’s proportional behavior.
With a setpoint / actual value deviation of 20 K, a setting of Xp = 20 produces a ma-
nipulated variable corresponding to the actuator’s running time.
The integral action time influences the controller’s integral behavior.
The derivative action time influences the controllers D-behavior. If the integral action
time is set to 0, the controller produces no PI behavior.
The plant’s behavior changes depending on the load. To ensure that the control system
will produce satisfactory results both in the upper and lower load range, different values
Connection conditions
Example
Giving consideration
to the load
Actuator running time
Note
Proportional band (Xp)
Integral action time Tn
Derivative action time Tv
Setting rules for Xp, Tn
and Tv
