52/106
Siemens
Basic Documentation RVP360
CE1P2546en
Building Technologies
12 Function block: Boiler
2017-07-24
SD
Switching differential
w
Boiler temperature setpoint
x
Actual value of boiler temperature
1
0
INT
max.
FG
B2
1
0
Y
B2
t
FGI
RSI
2
52
2D
09
0
1
0
t
t
t
t
Y
B1
max.
T
Kw
+ 0,5
*
SD
T
Kw
- 0,5
*
SD
T
Kx
RSI
FG
B2
Release for burner stage 2
t
Time
FGI
Release integral
T
Kw
Boiler temperature setpoint
INT
Integral
T
Kx
Actual value of boiler temperature
RSI
Reset integral
Y
B1
Control signal for burner stage 1
SD
Switching differential
Y
B2
Control signal for burner stage 2
12.4.3 Frost protection for the boiler
Frost protection for the boiler operates with fixed values:
Switch-on point: 5 °C boiler temperature
Switch-off point: Minimum limit of boiler temperature plus switching differential
If the boiler temperature falls below 5 °C, the burner is always switched on and
keeps running until the boiler temperature exceeds its minimum limit by the amount
of the switching differential.
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 temperature differential (minimum limit value minus
actual value) is integrated. From this, a critical locking signal is generated and
forwarded to the connected consumers. This causes the loads to reduce their
setpoints, aimed at consuming less energy. If the critical locking signal exceeds
a defined value, the boiler pump is deactivated as well.
If the boiler temperature returns to a level above the minimum limit, the integral is
reduced, resulting in a reduction of the critical locking signal.
If the integral falls below a defined level, the boiler pump is activated again. The
connected consumers increase their setpoints again.