eta TWIN 20 kW, Операция

Страница: 77 / 84

Heating value
77
depends on whether the wood is unsplit round logs,
metre-long split logs, or ready-to-burn split logs, and
on whether it is fresh from the forest or dried for
firewood.
The wood volume stays constant from when it is
freshly cut with a moisture content of 60% to the fibre
saturation point at 25%. The wood starts to contract if
dried below this point. It shrinks, and this is why air-
dried wood (moisture content of 15%) has more wood
substance per stere than freshly cut wood. The
difference is typically 5% to 6% for softwood, and 6%
to 9% for hardwood.
Logs are not straight. The longer the logs are, the less
wood and the more air is present per stere. There is
typically more air in "crooked" hardwood than in
"straight" softwood.
There is one further difference: round logs can typically
be stacked in a far more compact way than metre-long
split logs. If you split the wood yourself, buying round
logs will give you up to 15% more wood per stere.
In practice, deviations on the order of +/-10%
compared with theoretical values are to be expected.
Up to 20% is possible in extreme cases, not only
because the wood is particularly straight or crooked
but also because the density of the wood mass itself
can vary.
Incidentally, if you order a stere of ready-to-burn beech
firewood as 50 cm split logs from your wood dealer, the
dealer is entitled under current law to supply 0.85 m³ of
half-metre split logs cut from 1 m³ of metre-length split
logs. To avoid any unpleasant surprises, when
ordering ask how your dealer measures a stere (if the
price is good, you may find 0.85 m³ acceptable).
Estimating your wood requirements
Each kilowatt of heat output requires 0.9 steres of half-
metre split beech logs, or 1.3 steres of split spruce per
year.
In other words, 8 steres of half-metre split spruce logs
or 5.5 steres of beech will replace 1000 litres of
heating oil.
Energy content of one stere of wood in kilowatt hours
Round
logs
fresh-cut
1 m
Round
logs
dry
1 m
Split
logs
fresh-cut
1 m
Split
logs
dry
1 m
Split
logs
fresh-cut
50 cm
Split
logs
dry
50 cm
Split
logs
fresh-cut
33 cm
Split
logs
dry
33 cm
Moisture content 30-60% 15% 30-60% 15% 30-60% 15% 30-60% 15%
Softwood
1 stere contains 0.65 m³
1 stere contains 0.56
m³
1 stere contains 0.62
m³
1 stere contains 0.64
m³
Fir 1205 1269 1038 1093 1149 1210 1186 1249
Spruce 1299 1373 1119 1183 1239 1310 1279 1352
Douglas fir 1402 1478 1208 1274 1337 1410 1380 1455
Pine 1542 1625 1329 1400 1471 1550 1519 1600
Larch 1573 1656 1355 1427 1501 1580 1549 1631
Hardwood
1 stere contains 0.59 m³
1 stere contains 0.50
m³
1 stere contains 0.59
m³
1 stere contains 0.62
m³
Poplar 958 1020 812 864 958 1020 1007 1072
Willow 1107 1200 938 1017 1107 1200 1163 1261
Alder 1191 1270 1009 1076 1191 1270 1252 1335
Maple 1472 1550 1247 1314 1472 1550 1547 1629
Birch 1475 1570 1250 1331 1475 1570 1550 1650
Ash 1658 1760 1405 1492 1658 1760 1742 1849
Oak 1664 1760 1410 1492 1664 1760 1749 1849
Copper beech 1655 1800 1403 1525 1655 1800 1739 1892
Hornbeam 1743 1920 1477 1627 1743 1920 1832 2018
Black locust 1743 1920 1477 1627 1743 1920 1832 2018