Installation and operating instruction
Gas condensing unit WTC-GB 15-B Compact and WTC-GB 25-B Compact
7 Commissioning
83309302 1/2018-05 La
118-196
7.5 Calculate combustion heat rating
Formula sym-
bol
Explanation
V
B
Operating volume [m
3
/h]
Volume measured at gas meter at current pressure and
temperature (gas throughput).
V
N
Standard volume [m
3
/h]
Volume gained by gas at 1013 mbar and 0 °C.
f
Conversion factor
H
i
Calorific value [kWh/m
3
] (at 0 °C and 1013 mbar)
t
Gas
Gas temperature at gas meter [°C]
P
Gas
Pressure at gas meter [mbar]
P
Baro
Barometric air pressure [mbar], see table
V
G
Gas throughput determined at gas meter
T
M
Measuring time [seconds]
Q
F
Combustion heat rating [kW]
Determine current operating volume (gas throughput)
Measure gas throughput (V
G
) at gas meter, measuring time (T
M
) should be a min-
imum of 60 seconds.
Calculate operating volume (V
B
) using the following formula.
V
B
=
3600
V
G
T
M
Calculate conversion factor
Determine gas temperature (t
Gas
) and pressure (P
Gas
) at gas meter.
Determine barometric air pressure (P
Baro
) from table.
Height
above
sea level [m]
0
100
200
300
400
500
600
700
800
900
1000 1100 1200 1300
P
Baro
[mbar]
1013 1001 990
978
966
955
943
932
921
910
899
888
877
866
Calculate conversion factor (f) using the following formula.
f=
P
Baro
+ P
Gas
1013
273
273 + t
Gas
Calculate normal volume
Calculate the normal volume (V
N
) using the following formula.
V
N
= V
B
f
Calculate combustion heat rating
Calculate combustion heat rating (Q
F
) using the following formula.
Q
F
= V
N
H
i