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Calculation of gas flow
5.4
Formula symbol Description
V
Standard gas volume [Nm3/h]
N
Gas volume at normal condition 15 °C 1013 mbar
Q
Boiler output [kW]
Lower calorific value of gas [kWh/m
H
i
Natural gas under normal conditions 15 °C 1013 mbar, EN 676
η
Boiler efficiency (e. g. 90%)
f
Conversion factor (pressure and temperature compensation)
t
Gas temperature at gas meter [°C]
Gas
P
Barometric air pressure [mbar]
Baro
P
Pressure of gas at the gas meter [mbar]
Gas
V
Operating volume [m
Gas flow measured at the gas meter [m
VG
T
Measuring time for consumed gas quantity [s]
Calculate standard volume using the following formula:
Q
=
V
η
N
· H
i
Calculate conversion factor using the following formula:
273
=
f
273 + t
Gas
Calculate gas volume using the following formula:
V
N
V
=
f
Determine operating volume with the following formula:
3600 · V
G
=
V
T
Height above
sea level [m]
0
P
[mbar]
1013
Baro
Calorific value of the gas
Gas quality
Natural gas
G20
Natural gas
G25
Lower calorific value H
For exact calorific value of the gas, contact the gas distributor.
20
Bentone
3
/h]
450 kW
V
=
0.9 · 9.45 kW/m
N
+ P
P
Baro
Gas
·
f
1013
52.9 m
/h
3
V =
0.90
3600 · 1.58 m
V =
97 sek
100
200
300
400
1001
989
977
966
kWh/Nm
MJ/Nm
3
3
9.5
34.02
8.2
29.25
at normal conditions 15 °C and 1013 mbar, EN 676.
i
3
]
3
]
52.9 m
/h
=
3
3
273
945 + 20
·
=
273 + 15
1013
58.6 m
/h
=
3
3
58.6 m
/h
=
3
500
600
700
800
954
943
932
921
Gas quality
Butan
G30
Propan
G31
Example values
-
450 kW
3
9.45 kWh/m
0.9
-
15 °C
945 mbar
20 mbar
-
1.58 m
3
97 s
= 0.90
900
1000
1100
1200
910
899
888
877
kWh/Nm
MJ/Nm
3
3
32.25
116.09
24.44
88.00
172 535 24-2
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