Determining The Amount Of Fuel Required - Viessmann VITOFLEX 300-UF Technical Manual

Principles of wood combustion
Net calorific value for various types of wood, source: Technologie- und Förderzentrum (Technology and Support Centre) (TFZ)
Straubing, Bavaria, Germany
Water content in %
Type of tree
Spruce
Scots pine
Beech
Oak
Relation of moisture content (w) to moisture level in fuel (u)
The proportion of water in woodchips and wood pellets is given as
either the moisture content or the fuel moisture level. The moisture
content (in %) is relative to the moist fuel mass or the fresh sub-
stance (FS); the fuel moisture level is relative to the absolutely dry
fuel mass (TS).
70
60
50
40
30
20
10
0
0 20 40
Fuel moisture level (u) in %

Determining the amount of fuel required

The amount of fuel required can be calculated on the basis of the net
calorific value and the required rated heating output. Significant influ-
encing factors for this are the moisture content of the fuel and the
efficiency of the system.
Q
N
B =
H x η
u
VITOFLEX 300-UF
(cont.)
0
Unit of measurement
kWh/kg
kWh/smt
kWh/stcm
kWh/tcm
kWh/kg
kWh/smt
kWh/stcm
kWh/tcm
kWh/kg
kWh/smt
kWh/stcm
kWh/tcm
kWh/kg
kWh/smt
kWh/stcm
kWh/tcm
Example:
If 100 kg of fuel contains 50 kg of water, the fuel has a moisture con-
tent of 50 % (w50) and a fuel moisture level of 100 % (u = 100).
60 80 100
10 20 30
5.20 4.64 4.05
2245 2020 1979
1249 1177 1096
925 872 812
5.33 4.75 4.14
2613 2441 2239
1454 1354 1243
1077 1003 921
11.00 4.53 3.97
3475 3187 2899
1757 1613 1458
1432 1314 1188
5.00 4.50 3.92
3336 3091 2836
1687 1557 1432
1375 1269 1166
u [%] =
100 ― w [%]
120 140 160
40 50
3.44 2.86 2.27
1863 1805 1726
1039 1005 958
770 745 709
3.53 2.94 2.33
2170 2114 2009
1209 1170 1116
895 867 827
3.39 2.81 2.22
2704 2609 2482
1361 1315 1252
1109 1072 1020
3.33 2.66 2.19
2760 2576 2543
1396 1349 1283
1138 1099 1045
w [%]
x 100
180 200
Viesmann
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