Basic Documentation

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Siemens Modular Heating Controller RMH760B CE1P3133en
Building Technologies 6 Boiler temperature control 2017-09-29
After the burner has been shut down, pump overrun (refer to section 5.4 "Pump overrun
and mixing valve overrun") also acts on the bypass pump.
In addition to activating the bypass pump, locking signals are generated if required and
when a return temperature sensor is connected. If this is not required, setting "None" can
be selected for "Lock sig maintained boil ret temp".
If no return temperature is available, the bypass pump will be controlled parallel to
burner operation. The bypass pump always runs when released and when the basic
burner stage is on.
When using a boiler with mixing valve in the boiler return (plant type H4-x), maintained
boiler return temperature will be ensured by the separate mixing valve.
3133S73
MnPu
TBo
TRtBo
BoPu
VlvRtMx
VlvShOff
The 3-port mixing valve ensures both protective boiler startup and maintained boiler
return temperature.
The main pump can also be configured, in addition to the boiler pump. In that case, it
must be made certain that the main pump will not operate when the mixing valve is fully
closed. To prevent this, a bypass or overflow valve can be installed.
In this type of plant, the main pump provides the function of a system pump. And with
this type of plant, it must be made certain that the main pump will not operate when the
main controller’s mixing valve is fully closed. It is recommended not to use a mixing
valve in connection with the main controller.
To adapt the control parameters to the type of plant (actuator and controlled system),
the same setting parameters as those used with the mixing heating circuit are available.
For more detailed information, refer to section 5.7 "Mixing valve control".
Main menu > Commissioning > Settings > … or
Main menu > Settings > Boiler > Return control
Operating line
Range
Factory setting
Actuator run time
1…600 s
120 s
P-band Xp
1…100 K
50 K
Integral action time Tn
0…600 s
60 s
If a minimum return temperature shall be ensured, the minimum boiler temperature
must be selected accordingly. The minimum boiler temperature must be higher than the
minimum return temperature.
In the case of plants with mixing valve for the maintained boiler return temperature, the
mixing valve will be driven to the fully closed position when the return temperature
sensor is faulty and then deenergized to allow manual adjustment.
If no return temperature sensor is configured, a fault status message will appear.
If a return temperature sensor is configured but no return temperature limitation set, the
sensor will only be used for display purposes.
Control of the bypass
pump parallel to burner
operation
Maintained boiler return
temperature controlled
by mixing valve
Faulty return
temperature sensor