Limitation Of Boiler Temperature Differential - Siemens LMS14 User Manual

Fundamentals
Purpose of limiting the boiler's temperature differential
Additional parameters
Info/diagnostics
Building Technologies Division

6.39.3 Limitation of boiler temperature differential

When using a modulating heating circuit pump, the boiler temperature increase (that is,
the temperature difference of boiler return and boiler flow) is limited. As a result, the
current boiler flow temperature might not reach the flow temperature setpoint
demanded by the heating circuit.
Pump modulation in the heating circuit module calculates an increase of the flow
temperature setpoint, thus ensuring that the heating circuit's demand for heat can also
be satisfied when the pump's speed is reduced. An increase of the flow temperature
setpoint also leads to a higher boiler temperature setpoint. When, for the time being,
the return temperature remains at a constant level, an increase of the boiler
temperature setpoint always also results in a higher boiler temperature increase or
differential. To prevent thermal stress problems on the boiler due to a great boiler
temperature differential, the latter is limited when operating a modulating heating circuit
pump. Limitation of the boiler temperature differential is accomplished by limiting the
boiler temperature setpoint. For that, the boiler temperature setpoint is limited
depending on the acquired boiler return temperature. The extent of boiler temperature
setpoint limitation is selected such that the boiler temperature differential reached will
not be greater than the parameterized maximum (Temp differential max). As far as
permitted by the heat demand from the heating circuit, the LMS14... strives to keep the
boiler temperature differential at the level of the parameterized nominal differential
(Temp differential nominal).
Line no. Operating line
883 Pump speed max
1183 Pump speed max
1483 Pump speed max
2316 Temp differential max
2317 Temp differential nominal
Line no. Operating line
8310 Boiler temp
8311 Boiler setpoint
8314 Boiler return temp
User Manual LMS14...
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CC1U7471en
28.01.2015