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Siemens Building Technologies
Basic Documentation RVL471
CE1P2524E
HVAC Products
12 Function block "Boiler"
23.10.2002
12.4.4
Protective boiler startup
If the boiler temperature falls below the minimum limit of the boiler temperature while
the burner is running, the differential (minimum limit value minus actual value) will be
integrated. From this, a critical locking signal will be generated and transmitted to the
connected loads. This causes the loads to reduce their setpoints, thus consuming less
energy. If the critical locking signal exceeds a defined value, the boiler pump will be
deactivated also.
If the boiler temperature returns to a level above the minimum limit, the integral will be
reduced, resulting in a reduction of the critical locking signal. If the integral falls below a
defined level, the circulating pump will be activated again if it had been switched off.
The connencted loads rise their setpoint values.
When the integral reaches the value of zero, protective boiler startup will be deacti-
vated, in which case the critical locking signal is zero.
Protective boiler startup can be interrupted to ensure that, in the event of a burner fault,
for instance, frost protection for the plant will be provided.
In the case of protective boiler startup and simultaneous frost protection for the plant,
the boiler temperature gradient must turn positive within 15 minutes. Otherwise, the
locking signal will become invalid for at least 15 minutes. On completion of the 15 min-
utes, protective boiler startup will become active again as soon as the boiler tempera-
ture gradient turns positive.
If the boiler carries out protective boiler startup, the boiler temperature controller’s dis-
play shows
.
Protective boiler startup cannot be deactivated.
Section “25.4.7 Gain of locking signal” provides information on who receives the boiler
temperature controller's critical locking signal and how the consumers respond to it.
Controller 1
Plant type 2-1
Controller 1
Plant type 5-0
Controller 2
Controller 1 generates a critical locking
signal which deactivates the heating circuit
pump and the d.h.w. charging pump
Critical locking signal
LPB
Individual unit:
Interconnected plant:
25
24
B
0
2
e
Controller 1 switches
boiler pump off
Critical locking signal
Controller 3
12.4.5
Protection against boiler overtemperatures
To prevent heat from building up in the boilers (protection against overtemperatures),
the RVL471 offers a protective function.
When the first burner stage is switched off, the controller allows pump M1 to overrun for
the set pump overrun time (operating line 174 on the boiler temperature controller),
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 sig-
nal will be delivered to all loads in all segments. By contrast, if the boiler temperature
controller is located in segment 1...14, the signal will only be sent to the loads in the
same segment.
