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Vitocrossal 300 CA3 Series 2.5 to 6.0 Installation/Service
Function Description
Cascade Control Unit
(continued)
Conventional boiler strategy 1
Conventional boiler strategy 2
Benefit
The number of boilers in operation is the
lowest possible.
Set coding “3C:1“ in the “Cascade” group.
It is preferable to operate conventional
boilers at their upper output range, to reliably
prevent formation of condensate when return
temperatures are low.
An additional boiler will only be started if
the maximum output of all currently active
burners is insufficient to achieve the supply
temperature set value.
A boiler will be shut down when the
remaining boilers can achieve the required
output on their own.
Long burner run times.
Set coding “3C:2“ in the “Cascade” group
(factory set condition).
An additional boiler will only be started if
the maximum output of all currently active
burners is insufficient to achieve the supply
temperature set value.
A boiler will be shut down if the burners were
ramped down to their minimum output because
of a major negative control deviation and the
output is still too high.
Starting criterion
The boilers are started via a starting integral.
The next boiler in the boiler sequence will be
started if the value set in coding ”45” in the
“Cascade” group is exceeded.
The boilers are started via a starting integral.
The next boiler in the boiler sequence will be
started if the value set in coding ”45” in the
“Cascade” group is exceeded.
Shutdown criterion
A reduction in output causes the boilers to
shut down (Coding “3d:1“ in the “Cascade“
group). A boiler will be shut down when the
currently required output can be achieved
without the most recently started boiler.
The boilers are shut down via a shutdown
integral. When the shutdown integral exceeds
a limit set at coding “46” in the “Cascade”
group, the shutdown criterion is met and the
boiler started last will be shut down.
Conventional boiler strategies
Examples
Two-boiler system with modulating burners:
Boiler 1: 100% rated heating output
(base load set to 33%)
Boiler 2: 100% rated heating output
(base load set to 33%)
