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Building Technologies Division User Manual LMS14… CC1U7471en
6 The settings in detail 28.01.2015
In the boiler loop, the temperature is controlled to the preselected setpoint. The boiler is
used to supply heat to the heating circuits, the DHW heating equipment and the storage
tanks.
In DHW mode, a separate group of controller parameters are provided since a quick
response is required should the tap be opened.
The PID control algorithm calculates the required manipulated variable based on the
control deviation (T = temperature setpoint minus actual value) and the selected
control parameter settings. Using the control parameters, the respective controller part
can be activated/hidden or matched to the controlled system. The heat output called for
by the PID controller is limited to the permissible output range.
Due to the overriding 2-position controller, the aforementioned modulating control loop
is released and adjusted to the respective preselected setpoint. The result obtained by
the temperature controller is passed to the burner control as the preselected output in
percent.
In all situations, the limit thermostat overrides the temperature control loop. The limit
thermostat shuts down the boiler should its cutout temperature (Cutout temp LT
(2531))
be reached.
6.12.8 Heat output limits
The burner control ascertains the fan speed at which the burner maintains the minimum
output without loss of flame.
The maximum burner output in Heating mode can be preset via parameter in the form
of fan speed.
With the following operating modes, the heat output is statically preselected, which
means that the results obtained by the LMS14... are ignored, and a load value in
accordance with the function is forwarded to the burner control.
Function Required output
Chimney sweep Low-fire/high-fire/maximum heating load
Controller stop Controller stop output setpoint
6.12.9 2-position controller
The 2-position controller generates the signal for switching the burner control on and
off:
Startup = On at Actual value of boiler temperature < boiler temperature setpoint – switch-
on threshold
Shutdown = Off at Actual value of boiler temperature > boiler temperature setpoint + switch-
off threshold
The switching differentials are loaded depending on the type of compensation (DHW or
heating circuit). In addition, the dynamic switch-off differential influences the value of
the switch-off threshold (also refer to chapter Dynamic switching differentials).
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