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10.4.3. Frost protection for the boiler
10.4.4. Protective boiler startup
CE1P2522E / 30.03.2000
34/68
T
Kx
T
+ 0,5
SD
*
Kw
T
- 0,5
SD
*
Kw
Y
B1
1
0
INT
max.
0
FG
B2
1
0
Y
B2
1
0
FG
Release of burner stage 2
B2
FGI
Release limit
INT
Integral
RSI
Reset limit
SD
Switching differential
Frost protection for the boiler uses 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 will always be switched on until the
boiler temperature has crossed the minimum limit by the amount of the switching differ-
ential.
If, while the burner is running, the boiler temperature falls below the minimum limit of the
boiler temperature, the differential (minimum limit value minus actual value) will be inte-
grated. From this, a critical locking signal will be generated and transmitted to the con-
nected loads. This causes the loads to reduce their setpoints, thus consuming less en-
ergy. If the critical locking signal exceeds a defined value, the boiler pump will be deac-
tivated 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 reaches a
defined limit, the boiler pump will be activated again, and the connected loads raise their
setpoints again.
When the integral reaches the value of zero, protective boiler startup will be deactivated,
in which case the critical locking signal is zero.
Basic Documentation RVL470
Function block "Boiler"
FGI
RSI
t
Time
T
Boiler temperature setpoint
Kw
T
Actual value of the boiler temperature
Kx
Y
Control signal for burner stage 1
B1
Y
Control signal for burner stage 2
B2
max.
RSI
Siemens Building Technologies
Landis & Staefa Division
t
t
t
t
t
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