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Dynamic switch-off
differential
Notes
Siemens Building Technologies
HVAC Products
To prevent unnecessary boiler shutdowns during the settling phase, the switch-off
differential is dynamically adapted depending on the temperature progression.
In principle, the switch-off differential is reduced depending on the extent of overshoot
in the settling phase. With aperiodic processes, the reduction takes place via a time
criterion. The following graph shows a typical settling process:
Tist
SdAusMax
SdAusMin
Tsoll
SdEin
7494d20/0201
Dynamic switch-off differential
The switch-off differential is thus a function of the maximum temperatures «Tist
SdAus» = f (Tist, SdAusMax, SdAusMin)
The switch-on differential is ready parameterized. Depending on the operating mode, the
following assignments apply:
Heating mode
Min. switch-off differential
SdHzAusMin
(parameter)
Max. switch-off differential
SdHzAusMax
(parameter)
Switch-off differential
=f(SdHzAusMin,
SdAus
SdHzAusMax, TkIst)
Switch-on differential
=SdHzEin
SdEin (parameter)
Time to reduction to min.
ZsdHzEnde
switch-off differential
(parameter)
By setting the switching differential «SdHzAusMin» equal to «SdHzAusMax », or
«SdBwAus1Min» equal to «SdBwAus1Max», the dynamic switch-off differential can be
deactivated. The switching differentials are then adopted as ready parameterized.
A minimum switching differential of +2 K (SdAusMin, SdEin) must be observed.
The dynamic switch-off differential only works with positive values of SdAusMin and
SdAusMax!
Basic Documentation LMU54... / LMU64...
3 Functions
SdAus = f(Tist, SdAusMin, SdAusMax)
Tist
DHW storage tank
SdHzAusMin
SdHzAusMax
=f(SdHzAusMin,
SdHzAusMax, TkIst)
=SdHzEin
ZsdBwEnde
t
Instantaneous DHW
SdBwAus1Min
SdBwAus1Max
=f(SdBwAus1Min,
SdBwAus1Max, TbwIst1)
=SdBwEin1
ZsdBwEnde
53/171
CC1P7494en
07.11.2002
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