CE1P2522E / 30.03.2000
Basic Documentation RVL470
Siemens Building Technologies
34/68
Function block "Boiler"
Landis & Staefa Division
1
0
INT
max.
FG
B2
1
0
Y
B2
t
FGI
RSI
25
22D0
9
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 of burner stage 2
t
Time
FGI
Release limit
T
Kw
Boiler temperature setpoint
INT
Integral
T
Kx
Actual value of the boiler temperature
RSI
Reset limit
Y
B1
Control signal for burner stage 1
SD
Switching differential
Y
B2
Control signal for burner stage 2
10.4.3. Frost protection for the boiler
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.
10.4.4. Protective boiler startup
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.
