Siemens LMU54 Series, Основная документация

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Siemens Building Technologies Basic Documentation LMU54... / LMU64... CC1P7494en
HVAC Products 3 Functions 07.11.2002
3.5 Boiler control
Boiler control comprises all functions that convert the demand signal (boiler temperature
setpoint) to the output signal (PWM fan control).
These functions include:
•
The chimney sweep function (
→
CC1 B 7494)
•
The controller stop function (
→
CC1 B 7494)
•
Frost protection for the boiler
•
2-position control
•
Modulating control
•
Limitation and output of the manipulated variable
Frost protection for the boiler is ensured independently of the demand for heat or the
connected plant components. It is therefore checked autonomously in the boiler control
and, if required, triggers startup with a forced signal to carry the heat away from the boiler.
•
Activating frost protection for the boiler: TkIst < TkSfrostEin
When frost protection for the boiler is activated, the forced signal is delivered, thus
ensuring that the necessary amounts of heat are carried away from the boiler. The boiler
temperature setpoint for the PID controller used during frost protection for the boiler is
the maximum boiler temperature setpoint «TkSmax»:
TkSoll = TkSmax
This gives rise to a higher heat output, which means that the switch-off criterion will be
reached safely within a short period of time.
•
Terminating frost protection for the boiler: TkIst > TkSfrostAus
If there is no other or no greater demand for heat, shutdown will be initiated when the
switch-off criterion is reached and the forced signal canceled so that pump overrun
starts.
When there is additional demand for heat, there will be no shutdown when frost
protection for the boiler is terminated.
The controller delay serves for stabilizing the combustion conditions, especially after a
cold start.
After release of the controller by the burner control, the latter maintains the
parameterized heat output (parameter «LmodRgVerz») for the period of time predefined
by parameter «ZReglVerz». The modulating controller and thus modulation are released
only when this period of time has elapsed.
The following graph shows an example:
Output
t
Beginning
of startup
Ignition
(release of
fuel valves)
Start of
controller
delay time
Start of modulation
by the load controller
ZReglVerz
Ignition
7494d06aE
LmodRgVerz
Frost protection
for the boiler
Controller delay
Controller delay due to
parameterization