WOOD
Wood moisture is one of the most important features that affect its calorific value and consequently the quality of combustion. It is therefore important to use a timber with a moisture content not exceeding 20%. Why is this so?
1 kg of raw recently felled timber contains 0.5 liters of water, which significantly reduces the quality of combustion. Such a wood has substantially lower calorific value and a large part of the energy is consumed to evaporate this water, which ultimately means significantly higher fuel consumption and thus significantly higher heating costs.
Moreover, it comes by burning of wet wood to producing of smoke and water vapor, which are mutually linked, what causes a tar creation, which is undesirable, because it contains sulfuric acid. The wet wood burns poorly, gives less heat, produced smoke and shortens the life of the boiler and chimney.
Nowadays, it is important to recognize and respect that burning of wet wood has a negative impact on the environment in which you live.
By burning of correctly wood you achieve maximum performance, lower heating costs, easier cleaning and longer life of the boiler.
For further information we show below a table of influence of wood moisture on heating efficiency. From the table it can be seen that by burning of fresh wood will decrease the performance by 50% and fuel consumption will double.
Table of influence of wood moisture on heating efficiency :
| stored in months | moisture % | caloric value MJ/kg | wood consumption in kg | consumption in prm | costs in EUR/prm | costs in EUR/GJ | weight of 1prm in kg |
|
- |
0 | 18,1 | |||||
| 27 - 36 | 10 | 16,1 | 10 726 | 16,5 | 493 | 2,8 | 598 |
| 19 - 26 | 20 | 14,1 | 12 318 | 18,95 | 566 | 3,2 | 650 |
| 11 - 18 | 30 | 12,1 | 14 442 | 22,22 | 664 | 3,8 | 768 |
| 5 - 10 | 40 | 10,1 | 17 416 | 26,79 | 800 | 4,6 | 930 |
| 3 - 4 | 50 | 8,1 | 21 716 | 33,41 | 998 | 5,7 | 1177 |
| fresh wood | 60 | 6 | 29 317 | 45,1 | 1347 | 7,7 |
Heat consumption of the house at a loss of 20 kW is 175.9 GJ / year.
1prm wood = aproximately 650kg
prm = cubic meter
Fuel : beech, oak
Type : splitted
Price of 1prm = 33 Eur
Influence of wood moisture on its chemical composition and calorific value:
| fresh wood (50% of water content) | 1 year stored wood (30% of water content) | 2 years stored wood (20% of water content) | |
| caloric value | 8,1 MJ/kg | 12,1 MJ/kg | 14,1 MJ/kg |
| w - wood | w = 0,5kg = 50% | w = 0,214kg = 30% | w = 0,125kg = 20% |
| O - oxygen | O = 0,225kg = 22,5% | O = 0,225kg = 31,5% | O = 0,225kg = 36% |
| C - carbon | C = 0,250kg = 25% | C = 0,250kg = 35% | C = 0,250kg = 40% |
| H - hydrogen | H = 0,025kg = 2,5% | H = 0,025kg = 3,5% | H = 0,025kg = 4% |
| wood weight | 1kg | 0,714kg | 0,625kg |
From the table above it can be seen what happens to the wood by its drying. Raw wood with a weight of 1kg contains 0.5 kg of water. After one year, the water content is reduced to 30%, after 2 years the water content is reduced to 20%, thereby reducing also the weight of the fuel.
From the reason of reducing of the fuel weight the concentration of the active flammable substance will increase. Therefore also it is increasing the supplementary amount of energy, so its calorific value. Boiler user so burns the wood more efficiently, produces fewer emissions of pollutants, will reduce his consumption and extends the life of the boiler.
The best results when drying the wood you will achieve, when the wood will be under shelter and adequately ventilated.
We do not recommend to store the wood in the basement, because it can become moldy and rot, the wood deteriorates and loses its energy value.
Calorific value of the main types of firewood and its density:
| Fuel typea | Solids density | Density at 25% moisture | Caloric value at 25% moisture | ||||
| kg/m3 | kg/pm | kg/prm | MJ/kg | MJ/pm | MJ/prm | ||
| Beeech | 650 | 865 | 585 | 12,5 | 10 830 | 7 320 | |
| Oak | 630 | 840 | 565 | 13,2 | 11 050 | 7 430 | |
| Spruce | 430 | 575 | 415 | 13,1 | 7 350 | 5 440 | |
| Fir | 430 | 575 | 415 | 14 | 8 040 | 5 800 | |
| Pine | 510 | 680 | 495 | 13,6 | 9 250 | 6 730 | |
| Hornbeam | 680 | 905 | 610 | 12,1 | 10 970 | 7 400 | |
| Locust | 700 | 930 | 630 | 12,7 | 11 850 | 8 030 | |
| Poplar | 400 | 530 | 360 | 12,3 | 6 540 | 4 440 | |
| Willow | 500 | 665 | 450 | 12,8 | 8 490 | 5 740 | |
| Birch | 585 | 780 | 525 | 13,5 | 10 550 | 7 100 | |
|
PM = 1 m3 full of wood materials (solid cubic meter) PRM = 1 m3 of logs, contains about 60 - 75% of the wood (space meter) |
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The influence of moisture of main types of wood on its weight, power and caloric value:
| wood moisture 20% | wood moisture 30% | wood moisture 40% | wood moisture 50% | |||||||||
| weight | power | caloric value | weight | power | caloric value | weight | power | caloric value | weight | power | caloric value | |
| kg/m3 | kWh/kg | MJ/kg | kg/m3 | kWh/kg | MJ/kg | kg/m3 | kWh/kg | MJ/kg | kg/m3 | kWh/kg | MJ/kg | |
| Breech | 813 | 3,8 | 13,6 | 929 | 3,2 | 11,6 | 1083 | 2,7 | 9,6 | 1300 | 2,1 | 7,6 |
| Oak | 794 | 3,9 | 14,1 | 907 | 3,4 | 12,1 | 1058 | 2,8 | 10,1 | 1270 | 2,3 | 8,1 |
| Spruce | 538 | 3,9 | 14,1 | 614 | 3,4 | 12,1 | 717 | 2,8 | 10,1 | 860 | 2,3 | 8,1 |
| Fir | 531 | 4,2 | 15 | 607 | 3,6 | 13,0 | 708 | 3,1 | 11,0 | 850 | 2,5 | 9,0 |
Certified boilers for burning of wood :
- MODRATHERM ZEUS 25
- MODRATHERM ZEUS 30
- MODRATHERM ZEUS 35
- MODRATHERM ZEUS 40
- MODRATHERM ZEUS PYRO 26
- MODRATHERM ZEUS PYRO 30
- MODRATHERM ZEUS PYRO 36
- MODRATHERM ZEUS PYRO 42
- MODRATHERM PYROGAS 20
- MODRATHERM PYROGAS 26
- MODRATHERM PYROGAS 28
- MODRATHERM PYROGAS 37
- MODRATHERM PYROGAS 45
- MODRATHERM PYROGAS 55
- MODRATHERM PYROGAS 65
- MODRATHERM PYROSTAR DUO 18
- MODRATHERM PYROSTAR DUO 25
- MODRATHERM PYROSTAR DUO 30
- MODRATHERM PYROSTAR DUO 50