CrappieKeith
Addicted to ArboristSite
Have you heard the comment I mix in green wood to get a longer burn time.
It may work that way but the btu's available drop off greatly with wetter wood. Here's a chart...
http://www.google.com/url?sa=t&sour...0_-0qS_IlYF1EjYTg&sig2=1akWnaNK_uovkJQzyRDQoA
Juca also has this link that explains HHV vs LHV which may help consumers to understand ratings when purchasing a new appliance.
The Amount of Energy in Wood
Here's another set of intel that's helpful.
In the laboratory it is possible to get a heat value of 8,660 Btu/lb from wood fuel. This "high heat value" is obtained only with perfectly dry wood with 0% moisture content and in an atmosphere of pure oxygen. For laboratory use this is a useful number handy for theoretical problem analysis. But for the practical world it is unrealistic.
When wood is alive and fresh it consists primarily of water, i.e. most of the weight is actually water. After being cut to length and stacked for a year or two the average moisture content generally drops to approximately 20%.
In the combustion process water is evaporated and the temperature is raised to flue gas temperature.
Condition of Wood Approximate Combustion Values
btu/lb kJ/kg kcal/kg
Wet 4,000 9,300 2,220
Dry 7,000 16,300 3,890
6.3 lbs dry wood = 1 Boiler Horse Power
11.6 lbs wet wood = 1 Boiler Horse Power
Moisture Content and Usable Energy
Moisture Content and Usable Energy
Moisture Content
% Energy by Volume Unit
% Energy per Weight Unit
%
0 (oven dry) 100 100
20 (air-dry) 97 81
50 (green) 92 62
100 (wet) 85 42
Note that
by volume wet wood has about 85% of the energy of oven-dry wood
by weight wet wood has less than half - 42% - of the energy of oven-dry wood
One weight unit of wood has enough energy to evaporate 6 weight units of water.
John has an excellent article here that every novice should read.
http://www.hrt.msu.edu/energy/Notebook/Burning_wood_may_offer_heat_savings_by_Bartok.pdf
It may work that way but the btu's available drop off greatly with wetter wood. Here's a chart...
http://www.google.com/url?sa=t&sour...0_-0qS_IlYF1EjYTg&sig2=1akWnaNK_uovkJQzyRDQoA
Juca also has this link that explains HHV vs LHV which may help consumers to understand ratings when purchasing a new appliance.
The Amount of Energy in Wood
Here's another set of intel that's helpful.
In the laboratory it is possible to get a heat value of 8,660 Btu/lb from wood fuel. This "high heat value" is obtained only with perfectly dry wood with 0% moisture content and in an atmosphere of pure oxygen. For laboratory use this is a useful number handy for theoretical problem analysis. But for the practical world it is unrealistic.
When wood is alive and fresh it consists primarily of water, i.e. most of the weight is actually water. After being cut to length and stacked for a year or two the average moisture content generally drops to approximately 20%.
In the combustion process water is evaporated and the temperature is raised to flue gas temperature.
Condition of Wood Approximate Combustion Values
btu/lb kJ/kg kcal/kg
Wet 4,000 9,300 2,220
Dry 7,000 16,300 3,890
6.3 lbs dry wood = 1 Boiler Horse Power
11.6 lbs wet wood = 1 Boiler Horse Power
Moisture Content and Usable Energy
Moisture Content and Usable Energy
Moisture Content
% Energy by Volume Unit
% Energy per Weight Unit
%
0 (oven dry) 100 100
20 (air-dry) 97 81
50 (green) 92 62
100 (wet) 85 42
Note that
by volume wet wood has about 85% of the energy of oven-dry wood
by weight wet wood has less than half - 42% - of the energy of oven-dry wood
One weight unit of wood has enough energy to evaporate 6 weight units of water.
John has an excellent article here that every novice should read.
http://www.hrt.msu.edu/energy/Notebook/Burning_wood_may_offer_heat_savings_by_Bartok.pdf
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