Control Strategies - Viessmann VITOTRONIC 300 Installation And Service Instructions Manual

Cascade control
(cont.)

Control strategies

Condensing strategy
Benefit
Starting criterion
Shutdown criterion
Example (parameter "07:0" in the "Cascade" group)
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 %)
Start-up
100
66
33
0
100
33
0
200
150
100
33
0
Optimum utilisation of the condensing effect and long burner runtimes
Set parameter "07:0" in the "Cascade" group.
It is the aim of the condensing strategy to operate as many boilers as pos-
sible at the lowest output level.
An output statement causes the boilers to be started (parameter "08:1" in
the "Cascade" group).
An additional boiler will start if the current heat demand can also be cov-
ered by the currently active boilers plus the next boiler in the boiler se-
quence.
The boilers are shut down via a shutdown integral. If the shutdown integral
exceeds a limit set in parameter "0C" in the "Cascade" group, the last
started boiler is shut down.
Shutdown
t
System function description
100
66
33
0
100
33
0
200
150
100
33
0
t
137