Behavior When Burner Cycles - Siemens LMS14 User Manual

Additional parameters
Info/diagnostics
570/617
Building Technologies Division

6.39.2 Behavior when burner cycles

During burner off times, the system will reach a point where – after a certain period of
time – the supply of heat is no longer sufficient (current flow temperature lower than the
flow temperature setpoint). Speed control would respond to this situation by increasing
the pump's speed, but this would lead to shorter burner off times. Also, noise problems
would have to be expected due to higher pump modulation. For this reason, modulation
of the heating circuit pump was matched to cycling burner operation. When the burner
is shut down, pump modulation is maintained at the parameterized minimum speed.
When the burner is switched on, the speed of the heating circuit pump is kept constant
for an adjustable delay time. Modulation of the heating circuit pump is again calculated
and delivered only when the delay time has elapsed, based on the current common
flow temperature (boiler flow temperature). This means that the speed is increased only
when the filtered common flow temperature is lower than the flow temperature setpoint.
Higher pump speeds lead to longer burner running times. Filtering of the common flow
temperature then prevents quick speed reductions if the boiler temperature already lies
above the setpoint, but the burner's switch-off point is not yet reached. When the burner
is switched off, the pump's speed is reduced again to the parameterized minimum.
(Example of heating circuit 1)
Line no. Operating line
880
Pump speed reduction
882 Pump speed min
883 Pump speed max
888 Curve readj at 50% speed
889 Filter time const speed ctrl
890 Flow setp readj speed ctrl
[4291.1] Delay speed ctrl HC1
Line no. Operating line
8310 Boiler temp
8735 Speed heating circuit pump 1
8765 Speed heating circuit pump 2
8795 Speed heating circuit pump 3
User Manual LMS14...
6 The settings in detail
CC1U7471en
28.01.2015