Cold Start Of Plant - Siemens RWF 50.2 Installation, Use And Maintenance Instructions


Interlocking
Heating controller
Example

5.6 Cold start of plant

Note!
Functions Cold start of plant and Thermal shock protection (TSS) are interlocked.
Only one function can be activated, but never both at the same time.
When a heating system is switched off for a longer period of time, the actual value will
drop of course.
To achieve a faster control response, the controller immediately starts in high-fire
operation as soon as the control deviation (x-w) drops below a certain limit value.
This limit is calculated as follows:
Limit value = 2 x (HYS1-HYS3)
In that case, the response threshold (q) is inactive, independent of operating mode and
controlled variable (temperature or pressure).
Operating mode: Modulating, 3-position output
HYS1 = -5 K
HYS3 = +5 K
w = 60 °C
Limit value = 2 x (-5-5) = 2 x (-10) = -20 K
At an actual value below 40 °C, heating up immediately starts in low-fire operation, and
not in thermostat mode.
HYS3
HYS1
Figure 14: Control sequence Cold start of plant
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