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10.4.5. Protection against boiler overtemperatures
Siemens Building Technologies
Landis & Staefa Division
If the boiler effects protective boiler startup, the boiler temperature controller's display
shows
.
Protective boiler startup cannot be deactivated.
Section "13.4.7. Gain of locking signal" provides information on who receives the boiler
temperature controller's critical locking signal and how the loads respond to it.
Individual unit:
Controller 1 generates a critical locking signal
Controller 1
which deactivates the heating circuit pump
Plant type 2
Interconnected plant:
Controller 1
Plant type 5
Controller 1 switches
boiler pump off
Critical locking signal
To prevent heat from building up in the boilers (protection against overtemperatures),
the RVL470 offers a protective function.
When the first burner stage is switched off, the controller allows the boiler pump to over-
run for the set pump overrun time (operating line 174 on the boiler temperature control-
ler), generating at the same time a forced signal to all loads (inside the controller on the
data bus). If the boiler temperature controller is located in segment 0, the forced signal
will be delivered to all loads in all segments. By contrast, if the boiler temperature con-
troller is located in segment 1...14, the signal will only be sent to the loads in the same
segment.
Y
Boiler controller, stage 1
Pump
Forced signal
t
Time
Y
Control signal boiler pump
All loads (heating and d.h.w. circuits) and heat exchangers that abruptly reduce their
demand for heat watch the data bus during the set pump overrun time to see if a forced
signal is being sent by the boiler.
• If no forced signal is received, the loads and the heat exchanger only allow pump
overrun to take place (refer to section "13.4.4. Pump overrun")
• If, in this time window, a forced signal is received, the loads continue to draw heat
from the boiler in the following manner:
–
Plant types with heating circuits using a mixing valve maintain the previous setpoint
–
Plant types with pump heating circuits allow the pumps to continue running
Basic Documentation RVL470
Function block "Boiler"
Critical locking signal
LPB
Off
Overrun time
t
of boiler pump
Controller 2
Controller 3
CE1P2522E / 30.03.2000
35/68
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