Viessmann VITOTRONIC 300 Installation And Service Instructions Manual page 63

Vitotronic 300, GW5B & MW1B Installation and Service
Cascade Control of the Vitotronic 300-K
Conventional strategy 1
Benefit:
As few boilers as possible are active.
Set code "3C:1" in the "Cascade" group.
Conventional boilers are preferably operated at their upper
output range, to reliably prevent formation of condensate
due to low return temperatures. With this strategy, an
additional boiler will only be started if the maximum
output of all currently active burners is insufficient to
achieve the set supply temperature. A boiler will be shut
down when the remaining boilers can achieve the required
output on their own.
H 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 address "45" in the "Cascade" group is
exceeded (see page 93).
H Shutdown criterion:
Boilers are shut down via an output statement (code
"3D:1" in the "Cascade" group). A boiler is shut down
when the currently required output can be achieved
without the boiler that was started last.
Conventional strategy 2
Benefit:
Long burner runtimes.
Code "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 set supply temperature.
A boiler will be shut down if the burners were returned to
their minimum output because of a large negative control
deviation and the output is still too high.
H 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 address "45" in the "Cascade" group is
exceeded (see page 93).
H Shutdown criterion:
The boilers are shut down via a shutdown integral.
The shutdown criterion is met when the shutdown
integral exceeds a limit set via coding address "46" in
the "Cascade" group and the boiler started last will be
shut down.
(continued)
Condensing strategy (code "3C:0" in the "Cascade"
group)
Example for the different control strategies
Two-boiler system with modulating burners:
H Boiler 1: 100% rated output (base load set to 33%)
H Boiler 2: 100% rated output (base load set to 33%)
Starting
Shutdown
Function Description
t
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