Basic Documentation

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Siemens Modular Heating Controller RMH760B CE1P3133en
Building Technologies 10 DHW heating 2017-09-29
10.5 Direct DHW heating
3133S60
DHW 6
DHW heating takes place d
irectly via the heat
exchanger. Since there is no storage tank so
that charging control cannot be provided, control
is permanently enabled.
The setpoint to be delivered by the heat source
is made up of the current DHW setpoint plus the
setpoint increase o
f the heat exchanger.
For specific adaptation of the control parameters to the type of plant (actuator and
controlled system), additional setting parameters are available for direct DHW heating.
They apply to both 3-position and DC 0…10 V actuators.
Main menu > Commissioning > Settings > … or
Main menu > Settings > DHW > Controller primary circuit
Operating line
Range
Factory setting
Heat exchanger setp increase
0…50 K
10 K
Actuator running time opening
1…600 s
15 s
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
summer 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
characteristics. 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.
Settings
Connection conditions
Example
Giving consideration
to the load