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Building Technologies Division User Manual LMS14… CC1U7471en
6 The settings in detail 28.01.2015
6.39.7 Limitation to the nominal differential
As long as the modulating heating circuit pump is not controlled to maximum speed, the
parameterized nominal value Temp differential nominal (2317) applies.
Limitation of the boiler’s temperature differential to the nominal value is not raised
abruptly, but rather slowly in a linear manner from the last valid limitation level to the
nominal value.
The reduction of the boiler’s temperature differential to the nominal value follows a
ramp. The slope of the ramp depends on the time constant used for speed control
(Filter time const speed ctrl x (889/1189/1489)) and the difference between the
maximum and the nominal value of the boiler’s temperature differential. The ramp is
defined such that the transition from the maximum to the nominal value is made with
factor 5 of the relevant time constant.
If, for instance, a time constant of 3 minutes is parameterized for speed control, a
nominal value of 20 °C and a maximum of 35 °C for the boiler’s temperature differential,
the latter is raised by exactly 1 K per minute until the nominal differential is reached.
If, due the boiler’s temperature differential, the flow temperature remains below the flow
temperature setpoint called for by the heating circuit, speed control can increase the
volumetric flow by increasing pump modulation, thereby supplying more heat to the
heating circuit.
Line no. Operating line
889 Filter time const speed ctrl
1189 Filter time const speed ctrl
1489 Filter time const speed ctrl
2316 Temp differential max
2317 Temp differential nominal
Line no. Operating line
8310 Boiler temp
8311 Boiler setpoint
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