Siemens RVL481 - Minimum Limitation of the Boiler Temperature; Actions During D.h.w. Heating; 2-Position Control; Control with a Single-Stage Burner

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Siemens Heating and D.h.w. Controller RVL481 CE1P2541en
Building Technologies 12 Function block "Boiler" 20.05.2008
12.3.2 Minimum limitation of the boiler temperature
For minimum limitation of the boiler temperature, the minimum limit value can be ad-
justed. The switch-on point cannot fall below the minimum limit value. The switch-off
point will then be higher by the amount of the set switching differential
If the return temperature is limited, the display shows
.
12.3.3 Actions during d.h.w. heating
Both the maximum and the minimum limitation also act during d.h.w. heating.
12.4 2-position control
2-position control maintains the required boiler temperature by switching a single- or 2-
stage burner on and off.
The controller's commands to the burner or burner stages are delivered via the output
relays and indicated by LEDs.
12.4.1 Control with a single-stage burner
For 2-position control with a single-stage burner, the variables that can be set are the
switching differential and the minimum burner running time.
The controller compares the actual value of the boiler temperature with the setpoint. If
the boiler temperature falls below the setpoint by half the switching differential, the
burner will be switched on. If the boiler temperature exceeds the setpoint by half the
switching differential, the burner will be switched off.
2540D09
T
K
ON
OFF
T
Kw
0.5×SD 0.5×SD
SD Switching differential
TK Boiler temperature
TKw Boiler temperature setpoint
If there is no more deviation before the minimum burner running time has elapsed, the
burner will nevertheless continue to operate until that period of time is completed
(burner cycling protection). This means that the minimum burner running time has prior-
ity. Maximum limitation of the boiler temperature will be maintained, however, which
always leads to burner shutdown.
T
Kw
+ 0,5×SD
0
1
2540D10
T
K
T
Kw
T
Kw
- 0,5×SD
T
Kx
t
Y
B
SD Switching differential T
Kw
Boiler temperature setpoint
t Time T
Kx
Actual value of boiler temperature
T
K
Boiler temperature Y
B
Burner control signal
When controlling a single-stage burner, the reset limit of the second stage should be
set to zero.
Note