Determining The Wood Fuel Demand - Viessmann VIESMANN VITOLIGNO 300-H Technical Manual

Principles of wood combustion
Water content in %
Type of tree
Beech
Oak
Poplar
Relation of water content to moisture level in fuel
The proportion of water in wood fuels is given as either the water con-
tent or the fuel moisture level. The water content (in %) is relative to
the moist fuel mass or the fresh substance (FS); the fuel moisture level
is relative to the absolutely dry fuel mass (TS). The specifications for
Köb products use the water content w.
70
60
50
40
30
20
10
0
0 20 40
Fuel moisture level (u) in %

Determining the wood fuel demand

The amount of wood fuel required can be calculated on the basis of
the net calorific value and the required rated heating output. Significant
influencing factors for this are the water content of the fuel and the
efficiency of the system.
B =
B Amount of fuel required in kg/h
Q Required rated heating output in kW
N
VITOLIGNO 300-H
(cont.)
0
Unit of measurement
kWh/kg 5.00
kWh/smt 2790
kWh/stcm 1953
kWh/tcm 1116
kWh/kg 5.00
kWh/smt 2355
kWh/stcm 1999
kWh/tcm 1142
kWh/kg 5.00
kWh/smt 1765
kWh/stcm 1236
kWh/tcm
Example:
If 100 kg of fuel contain 50 kg water, the fuel has a water content of
50 % (w50) and a fuel moisture level of 100 % (u=100).
60 80 100
Q
N
H x η
u
H
η
5 10 15
4.72 4.43 4.15
2770 2748 2723
1939 1923 1906
1108 1099 1089
4.72 4.43 4.15
2835 2812 1786
1984 1968 1951
1134 1125 1115
4.72 4.43 4.15
1752 1738 1723
1227 1217 1206
706 701 605
120 140
Net calorific value kWh/kg
u
System efficiency in %
20 25 30
3.86 3.58 3.30
2695 2664 2627
1887 1864 1839
1078 1065 1051
3.86 3.58 3.30
2758 2726 2689
1931 1908 1882
1103 1090 1075
3.86 3.58 3.30
1705 1685 1662
1193 1179 1163
680 682 674 665
160 180 200
VIESMANN
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