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Building Technologies
Modular Heating Controller RMH760B
CE1P3133en
HVAC Products
6 Boiler temperature control
05.02.2007
313
3S
73
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.
6.6.12 Protection against pressure shocks
Main menu > Commissioning > Settings > …
or
Main menu > Settings > Boiler > Limitations
Operating line
Range
Factory setting
Delta boiler temp max (stage 2)
0…10 K
1 K
To prevent pressure shocks in the gas network when stages 1 and 2 are simultane-
ously switched off, stage 2 is switched off before the maximum boiler temperature is
reached, the difference being “Delta boiler temp max (stage 2)“.
When the boiler is locked, stage 1 is switched off after stage 2, the difference in time
being 10 seconds.
Faulty return tempera-
ture sensor