12
Bentone
3.7
Calculation of gas flow
Formula
symbol
Description
Example
values
V
N
Standard gas volume [Nm3/h]
Gas volume at normal condition 15 °C 1013 mbar
-
Q
Boiler output [kW]
80 kW
H
i
Lower calorific value of gas [kWh/m
3
]
Natural gas under normal conditions 15 °C 1013 mbar, EN 676
9.45 kWh/m
3
η
Boiler efficiency (e. g. 90%)
0.9
f
Conversion factor (pressure and temperature compensation)
-
t
Gas
Gas temperature at gas meter [°C]
15 °C
P
Baro
Barometric air pressure [mbar]
945 mbar
P
Gas
Pressure of gas at the gas meter [mbar]
20 mbar
V
Operating volume [m
3
/h]
-
VG
Gas flow measured at the gas meter [m
3
]
0.26 m
3
T
Measuring time for consumed gas quantity [s]
90 s
V
N
=
Q
V
N
=
80 kW
=
9.4 m
3
/h
η
· H
i
0.9 · 9.45 kW/m
3
Calculate standard volume using the following formula:
f
=
273
x
P
Baro
+ P
Gas
f
=
273
·
945 + 20
= 0.90
273 + t
Gas
1013
273 + 15
1013
Calculate conversion factor using the following formula:
V
=
V
N
V
=
9.4 m
3
/h
=
10.4 m
3
/h
f
0.90
Calculate gas volume using the following formula:
V
=
3600 · V
G
V
=
3600 · 0.26 m
3
=
10.4 m
3
/h
T
90 sek
Determine operating volume with the following formula:
Gas quality
kWh/Nm
3
MJ/Nm
3
Natural gas
G20
9.5
34.02
Natural gas
G25
8.2
29.25
Calorific value of the gas
Lower calorific value H
i
at normal conditions 15 °C and 1013 mbar, EN 676.
For exact calorific value of the gas, contact the gas distributor.
172 535 24
Height above
sea level [m]
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
P
Baro
[mbar]
1013 1001
989
977
966
954
943
932
921
910
899
888
877
Gas quality
kWh/Nm
3
MJ/Nm
3
Butan
G30
32.25
116.09
Propan
G31
24.44
88.00
Summary of Contents for STG 146i/2
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