Cascade Control - Viessmann VITOTRONIC 300 Installation And Service Instructions Manual

Cascade control

Brief description
The common flow temperature is regulated by starting
or stopping the burners or by starting/stopping individ-
ual burner stages.
Operation is via 2 control modes:
■ Standalone control (see page 136)
Sequential control (see page 136)
■
Set common flow temperature
The set common flow temperature is determined from
the following parameters:
■ Set flow temperature for heating circuit 1 without
mixer, and heating circuits 2 and 3, each with mixer
■ Set flow temperature of further consumers
Set DHW temperature
■
External demands
■
Control range limits:
■ Upper control range limits:
Maximum system flow temperature limit (parameter
"02" in the "Cascade" group).
Lower control range limits:
■
Minimum system flow temperature limit (parameter
"01" in the "Cascade" group).
Common flow temperature control
110
A
80
D
8 K
+20
Outside temperature in °C
Fig. 42
Maximum flow temperature limit (parameter "02" in
A
the "Cascade" group)
B Slope = 1.8 for heating circuit without mixer
Slope = 1.2 for heating circuit with mixer
C
Common flow temperature (at a differential tem-
D
perature = 8 K)
Lower common flow temperature
E
A control strategy is set for each control type:
Condensing strategy (see page 137)
■
■ Conventional boiler strategy 1 (see page 138)
■ Conventional boiler strategy 2 (see page 138)
Differential temperature:
■ The differential temperature can be set in parameter
"0C" in the "General" group.
■ Delivered condition 8 K.
■ The differential temperature is the value by which the
common flow temperature should be higher than the
highest currently required flow temperature of the
heating circuit with mixer.
■ System with only one heating circuit with mixer:
The common set flow temperature is regulated auto-
matically to 8 K above the set flow temperature of
the heating circuit with mixer.
System with heating circuit without mixer and heating
■
circuits with mixer:
The common set flow temperature operates in
accordance with its own heating curve. The differen-
tial temperature of 8 K towards the set flow tempera-
ture of the heating circuits with mixer is set at the
factory.
B
C
E
-20
System function description
135