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Appendix - Firing rate on basis of air density
D
The firing rate of the burner shown in the manual is valid for a
room temperature of 20 °C and an altitude of 0 m above sea level
(barometric pressure around 1013 mbar).
It may be that a burner has to operate with combustive air at a
higher temperature and/or higher altitudes.
The heating of the air and the increase in altitude produce the
same effect: the expansion of the air volume (i.e. the reduction of
its density).
The delivery of the burner fan remains essentially the same, but
3
the oxygen per m
of air, and the thrust (discharge head) of the
fan are reduced.
It is therefore important to know if the maximum output requested
from the burner at a determinate combustion chamber pressure
remains within the firing rate of the burner even with the changed
temperature and altitude conditions.
To check it, proceed as follows:
1 -Find the corrective factor F (relating to the air temperature and
altitude of the system) in the table alongside.
2 -Divide the output Q required from the burner by F to obtain the
equivalent output Qe:
Qe = Q : F (kW)
3 - In the firing rate of the burner, mark the work point identified by:
Qe = equivalent output
H1 = pressure in combustion chamber
point A that must remain within the firing rate (Fig. 41).
Average baro-
Altitude
metric pressure
m. above sea
mbar
level
0
1013
100
1000
200
989
300
978
400
966
500
955
600
944
700
932
800
921
900
910
1000
898
1200
878
1400
856
1600
836
1800
815
2000
794
2400
755
2800
714
3200
675
3600
635
4000
616
mbar
mbar
H2
H3
H1
D388
Fig. 41
20022445
0
5
1.087
1.068
1.073
1.054
1.061
1.042
1.031
1.050
1.037
1.018
1.025
1.007
1.013
0.995
1.000
0.982
0.988
0.971
0.977
0.959
0.964
0.946
0.942
0.925
0.919
0.902
0.897
0.881
0.875
0.859
0.852
0.837
0.810
0.796
0.766
0.753
0.724
0.711
0.682
0.669
0.661
0.649
A
Qe
Qe
kW
kg/h
4 -Trace a vertical line from point A, Fig. 41, and find the maxi-
mum pressure H2 of the firing rate.
5 -Multiply H2 by F to obtain the maximum lowered pressure H3
of the firing rate
H3 = H2 x F (mbar)
If H3 is greater than H1, as in Fig. 41, the burner can produce the
delivery requested.
If H3 is less than H1, it is necessary to reduce the output of the
burner. The reduction in output is accompanied by a reduction in
the combustion chamber pressure:
Qr = reduced output
H1r = reduced pressure
H
r = H
1
Example, 5% reduction in output:
Qr
= Q x 0.95
H1r = H1 x (0.95)
With the new values - Qr and H1r - repeat steps 2 - 5.
Warning:
the combustion head should be adjusted in relation to the equiv-
alent output Qe.
F
Air temperature °C
10
15
1.049
1.031
1.013
1.035
1.017
1.000
1.024
1.006
0.989
1.013
0.995
0.978
1.000
0.983
0.966
0.989
0.972
0.955
0.977
0.960
0.944
0.965
0.948
0.932
0.954
0.937
0.921
0.942
0.926
0.910
0.930
0.914
0.898
0.909
0.893
0.878
0.886
0.871
0.856
0.866
0.851
0.836
0.844
0.829
0.815
0.822
0.808
0.794
0.782
0.768
0.755
0.739
0.726
0.714
0.699
0.687
0.675
0.657
0.646
0.635
0.638
0.627
0.616
53
GB
( )
Qr
2
x
1
Q
2
20
25
30
0.996
0.980
0.983
0.967
0.972
0.956
0.962
0.946
0.950
0.934
0.939
0.923
0.928
0.913
0.916
0.901
0.906
0.891
0.895
0.880
0.883
0.868
0.863
0.849
0.842
0.828
0.822
0.808
0.801
0.788
0.781
0.768
0.742
0.730
0.702
0.690
0.664
0.653
0.624
0.614
0.606
0.596
40
0.948
0.936
0.926
0.916
0.904
0.894
0.884
0.872
0.862
0.852
0.841
0.822
0.801
0.783
0.763
0.743
0.707
0.668
0.632
0.594
0.577
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