Wood
The moisture content of wood is one of the most important properties that affects its calorific value and consequently the quality of combustion. It is therefore important to use wood with a moisture content of no more than 20%. Why is this so?
1 kg of raw, recently harvested wood contains 0.5 liters of water, which significantly reduces the quality of combustion. Such wood has a significantly 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.
In addition, when burning wet wood, smoke and water vapor are formed, which bind with each other and tar is formed, which is undesirable because it contains sulfuric acid. Wet wood burns poorly, gives less heat, smoke is formed and the life of the boiler and chimney is shortened.
Nowadays it is important to realize and respect that burning wet wood has a negative impact on the environment in which you live.
By burning the right wood, you will achieve maximum performance, lower heating costs, easier cleaning and a longer boiler life.
For more information, we present below a table of the impact of wood moisture on heating efficiency. The table shows that burning fresh wood will reduce your performance by 50% and double your fuel consumption.
Table of the influence of wood moisture on heating efficiency
| stored in months | moisture % | caloric value MJ/kg | wood consumption in kg | wood 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 |
| čerstvé drevo | 60 | 6 | 29 317 | 45,1 | 1347 | 7,7 |
The heat consumption of the house with losses of 20 kW is 175.9 GJ/year.
1 prm of wood = approx. 650kg
prm = spatial meter
Fuel: beech, oak
Type: chopped
Price 1 prm = 60 Eur
The 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 weigth | 1kg | 0,714kg | 0,625kg |
The table above shows what happens to wood when it is dried. Raw wood weighing 1 kg contains 0.5 kg of water. After one year, the water content decreases to 30%, and after 2 years, the water volume decreases to 20%, which also reduces the weight of the fuel.
Due to the reduction in the weight of the fuel, the concentration of active combustible substances increases. Therefore, the specific energy, i.e. its calorific value, increases. The boiler user thus burns wood more efficiently, produces fewer emissions of pollutants, reduces consumption and extends the life of the boiler.
You will achieve the best drying results if the wood is under cover and sufficiently ventilated.
We do not recommend storing wood in a cellar, as the wood can become moldy and rot, which degrades the wood and loses its energy value.
Calorific value of the main types of firewood and their density:
| Fuel type | Solids density | Density at 25% moisture | Caloric value at 25% moisture | ||||
| kg/m3 | kg/pm | kg/prm | MJ/kg | MJ/pm | MJ/prm | ||
| Beech | 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 effect of moisture content of the main types of wood on its weight, thermal output and calorific value:
| wood moisture 20% | wood moisture 30% | wood moisture 40% | wood moisture 50% | |||||||||
| weight | output | caloric value | weight | output | caloric value | weight | output | caloric value | weight | output | 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 |
You can burn wood in these boilers:
- MODRATHERM ZEUS 25
- MODRATHERM ZEUS 30
- MODRATHERM ZEUS 35
- MODRATHERM ZEUS 40
- 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