Datasheet

5822 239
G
B5822 239
G
B
11
2.5 Flue gas re-circulation
2.5 Flue gas re-circulation
Sizing the flue gas system
Calculating the cross-sections of the flue
gas system is the basis of and a
pre-requisite for the proper function of
any flue gas system.
You can determine the cross-section of
the flue gas system depending on the
rated output and the effective height of
the flue gas systems using the following
cross-section diagram.
DIN 4705 was taken into consideration in
calculating the cross-section diagram.
These calculations are based on the
following parameters:
H Flue gas temperature downstream of
the draught hood approx. 120 ºCand
ambient temperature + 15 ºC. Higher
flue gas temperatures generally only
improve the draught a little.
H The effective flue gas system height
equals the height difference between
the boiler flue connection and the flue
gas outlet.
H Length of the connection piece max. ¼
of the effective flue gas system height,
but not more than 7 m.
The connection adapter and flue gas
system should have the same
cross-section.
H Drag coefficient Σζ for reversing, inlet,
shape and velocity alterations equals
2.2 (diagram acc. to Schiedel).
H The drag coefficient Σζ = 2.2 covers, for
example, the losses of a connection
adaptor with an inlet less than 10 º and
two bends of 90 º and an increase in
velocity which may possibly be
required.
H We recommend that flue gases enter
the flue gas system at an angle of less
than 45 º.
Chimney diagram
Check, when applying the diagram,
whether the parameters for calculating
the flue gas temperature, length of
connection piece and of the drag
coefficient have been maintained.
In case of more severe deviations, the
technical departments of flue gas system
manufacturers will calculate
cross-sections, which are accurately
matched to each individual project.
Diagram for circular cross-sections (Schiedel)
The diagram shown is also a valid representation for other manufacturers. The installing contractor should check how far this
diagram may be applied to the flue gas systems of other manufacturers.
Clearance cross-section in cm
50
45
40
35
30
25
22
20
18
60
70
80
90
100
150
200
250
300
350
400
450
500
600
700
800
900
1000
555 1015202530
Effective height of the flue gas systems in metres
Rated output in kW