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Building Technologies Division User Manual LMS14… CC1U7471en
6 The settings in detail 28.01.2015
Objective:
The boiler shall be enabled to supply as much heat as possible to the storage
tank.
The boiler pump shall modulate its speed in a way that the current setpoint (DHW or
buffer storage tank) is reached at the boiler flow. The boiler pump’s speed shall be
increased within predefined limits until the burner reaches its upper capacity limit. For
modulation of the boiler pump in DHW mode, the PWM limits of the DHW charging
pump apply, in Heating mode, the PWM limits of the boiler pump. Speed control of the
boiler pump reduces the boiler’s water throughput (pump speed) to such an extent that
the required boiler flow temperature setpoint will be reached. For that, the setpoint fed
to speed control is not the same as that forwarded to the LMS14...; the setpoint used
for speed control is lower. This ensures that the pump’s speed is increased before the
flow temperature setpoint is reached.
This prevents the boiler from reaching its setpoint at reduced output only because the
pump runs at a lower speed. In that case, only part of the boiler’s output would be used.
The speed is calculated by a PID controller.
At low boiler output (current output below 66%), the setpoint for speed control is
reduced by an adjustable value. If the relative boiler output exceeds 66%, the setpoint
for speed control is increased in such a way that the setpoint for speed calculation at
100% boiler output corresponds to the request for heat.
The function is selected via enumeration Boiler setpoint of parameter Pump modulation
(2320).
Setpoints
Speed
setpoint
10 °C
7471d12e/1214
Figure 87: Boiler pump – Speed control depending on the boiler temperature setpoint
The diagram shows a setpoint reduction of 10 °C. It can be parameterized.
Speed control
depending on the boiler
temperature setpoint
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