36
Legend:
Q
N
= Appliance rating [kW]
η = Efficiency [%]
H
i
= Calorific value [kWh/m
3
]
H
i,B
= Operating calorific value [kWh/m
3
]
f = Conversion factor
P
Baro.
= Barometric pressure [mbar]
P
G
= Gas pressure at meter [mbar]
t
G
= Gas temperature at meter [°C]
Appendix
Calculation of gas throughput
Average yearly air pressure
Average geodetic height from 1 51 101 151 201 251 301 351 401 451 501 551 601 651 701
of installation to 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
Average yearly air pressure mbar 1016 1013 1007 1001 995 989 983 977 971 965 959 953 947 942 936 930
above sea level
950 956 962 967 973 979 985 991 997 1003 1009 1015 1021 1027 1033 1036
0 0·9378 0·9437 0·9497 0·9546 0·9605 0·9664 0·9724 0·9783 0·9842 0·9901 0·9961 1·0020 1·0079 1·0138 1·0197 1·0227
2 0·9310 0·9369 0·9427 0·9476 0·9535 0·9594 0·9653 0·9712 0·9770 0·9829 0·9888 0·9947 1·0006 1·0064 1·0123 1·0153
4 0·9243 0·9301 0·9359 0·9408 0·9466 0·9525 0·9583 0·9642 0·9700 0·9758 0·9817 0·9875 0·9933 0·9992 1·0050 1·0079
6 0·9176 0·9234 0·9292 0·9341 0·9399 0·9457 0·9514 0·9572 0·9630 0·9688 0·9746 0·9804 0·9862 0·9920 0·9978 1·0007
8 0·9111 0·9169 0·9226 0·9274 0·9332 0·9389 0·9447 0·9504 0·9562 0·9619 0·9677 0·9734 0·9792 0·9850 0·9907 0·9936
10 0·9047 0·9104 0·9161 0·9209 0·9266 0·9323 0·9380 0·9437 0·9494 0·9551 0·9609 0·9666 0·9723 0·9780 0·9837 0·9866
12 0·8983 0·9040 0·9097 0·9144 0·9201 0·9257 0·9314 0·9371 0·9428 0·9484 0·9541 0·9598 0·9655 0·9711 0·9768 0·9796
14 0·8921 0·8977 0·9033 0·9080 0·9137 0·9193 0·9249 0·9306 0·9362 0·9418 0·9475 0·9531 0·9587 0·9644 0·9700 0·9728
16 0·8859 0·8915 0·8971 0·9017 0·9073 0·9129 0·9185 0·9241 0·9297 0·9353 0·9409 0·9465 0·9521 0·9577 0·9633 0·9661
18 0·8798 0·8854 0·8909 0·8955 0·9011 0·9067 0·9122 0·9178 0·9233 0·9289 0·9344 0·9400 0·9456 0·9511 0·9567 0·9594
20 0·8738 0·8793 0·8848 0·8894 0·8949 0·9005 0·9060 0·9115 0·9170 0·9225 0·9281 0·9336 0·9391 0·9446 0·9501 0·9529
22 0·8679 0·8734 0·8788 0·8834 0·8889 0·8944 0·8998 0·9053 0·9108 0·9163 0·9218 0·9273 0·9327 0·9382 0·9437 0·9464
24 0·8620 0·8675 0·8729 0·8775 0·8829 0·8883 0·8938 0·8992 0·9047 0·9101 0·9156 0·9210 0·9265 0·9319 0·9373 0·9401
Gas temperature t
G
[°C]
1 mbar = 1 hPa = 10·20 mm w.g. 1 mm w.g. = 0·0981 mbar = 0·0981 hPa
Total pressure P
Baro.
+ P
Gas
[mbar] ➞
➞
To provide the correct thermal input to the heat exchanger,
the required gas throughput must be determined
beforehand.
Conversion from standard to operating conditions
The calorific value (H
i
) of combustible gases is generally
given in relation to the standard barometric conditions (0°
C, 1013 mbar).
Example:
Height above sea level = 500 m
Barom. air pressure P
Baro.
fromTab. = 953 mbar
Gas pressure P
G
at meter = 20 mbar
Total pressure P
meas.
(B
o
+P
G
) = 973 mbar
Gas temperature t
G
=10°C
Conversion factor f from Tab. = 0·9266
Appliance rating Q
N
=95kW
Efficiency η (assumed) = 91 %
Calorific value H
i
= 10·35 kWh/m
3
Normal volume:
Q
N
V
N
=
η • H
i
Operating volume
V
N
Q
N
V
B
=orV
B
=
f η • H
i,B
Measuring time in seconds for 1m
3
of gas throughput
3600 • 1 [ m
3
]
Measuring =
time [s] V
B
[ m
3
/h ]
The figures in the table are based on the following simple
formula:
P
Baro
+ P
G
273
f= •
1013 273 + t
G
The moisture content of the gas is negligible and therefore
is not considered in the table. The table allows for
conversion factors in the low pressure range (up to > 100
mbar).
The factor can also be determined in the high pressure
range according to the formula to the left.
Determination of factor f
95
V
N
= → V
N
≈ 10·1 m
3
/h
0·91 • 10·35
10·1
V
B
= → V
B
≈ 10·9 m
3
/h
0·9266
Measuring time when gas meter reads 1m
3
:
3600
Measuring =–––––– → Measuring ≈ 330 s
time [s] 10·9 time [s]
For two stage version calculate and check partial load in
the same way.
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