154
Example
10
0
20
30
30
40
50
60
6
7
8
9
Set flow temperature
in
°C
Time
A
B
C
D
Fig. 114
A
Start of operation at standard room temperature or
comfort room temperature
B
Set flow temperature in accordance with the set
heating curve
C
Set flow temperature in accordance with parame-
ter 424.3
D
Duration of operation with higher set flow tempera-
ture in accordance with parameter 424.4:
60 min
Electronic combustion controller of gas condensing module
The electronic combustion controller utilises the physi-
cal correlation between the level of the ionisation cur-
rent and the air ratio
λ
. The maximum ionisation cur-
rent is achieved at an air ratio of 1 for all gas qualities.
The ionisation signal is evaluated by the combustion
controller and the air ratio is adjusted to a value
between
λ
=1.24 and 1.44. This range provides for an
optimum combustion quality. The gas train regulates
the required amount of gas subject to gas quality.
To check the combustion quality, the CO
2
content or
the O
2
content of the flue gas is measured. The pre-
vailing air ratio is determined using the actual values.
The correlation between CO
2
or O
2
content and air
ratio
λ
is shown in the following table.
To achieve optimum combustion control, the system
regularly carries out an automatic self-calibration; also
after power failures (shutdown). For this, the combus-
tion is briefly regulated to maximum ionisation current
(corresponding to air ratio
λ
=1). Self-calibration takes
place shortly after the burner starts and lasts for 20 s
approx. During calibration, higher than normal CO
emissions may occur briefly.
Electrical output of the fuel cell
Electrical output is influence by the gas quality and the
geodetic head. Electrical output is also reduced by a
decrease in the fuel cell's electrical efficiency over
time.
Vitovalor PT2 is operated with constant heat input (gas
input) and constant overall efficiency. This means that
the ratio of electrical output to thermal output changes
over the service life. As the overall output remains con-
stant, electrical output decreases over the service life
while thermal output increases.
Function description
Control functions
(cont.)
5853335
Functions
