Atmosphere

Review of literature on residential firewood use, wood-smoke and air toxics

Technical Report No. 4
Environment Australia, June 2002
ISBN 0 6425 4868 4

Conversion Factors

1 calorie (cal) = 4.184 J (energy to heat 1 g H2O by 1°C)
1 kWh = 3.6 MJ
1 British thermal unit (Btu) = 1055 J (energy to heat 1 lb H2O by 1°F)
1 MBtu = 1.055 GJ
1 horsepower hour (hp h) = 2.685 MJ

1 Btu/h = 0.293 W
1 MBtu/h = 293 kW
1 therm/h = 29.307 kW

1 Btu/lb = 2.326 kJ/kg = 2.326 MJ/t

Measurement of wood and firewood volume

1 cord = 4 ft x 4 ft x 8 ft = 128 ft3 = 3.62 m3 (total stack volume)
solid wood in a stack is 45% to 80 % of volume
usual figures are 67% or 75% (for split straight wood use 75%)
1 cord ≈ 2.7 m3 solid wood
1 super foot = 1 ft x 1 ft x 1 in = 0.00236 m3
1 hoppus super foot = 0.7854 super feet
1 'unit' = 200 ft3 uncompressed woodchips or wood waste = 5.66 m3 ( uncompressed woodchips have approx. half bulk density of solid wood)
1 cord produces approx. 1 unit of woodchips
Volume of woodchips reduces by approx. 33% on vibration

Some Energy Contents of Wood and Bark (approximate)
Hardwood (oven-dry) 20 MJ/kg (high heat value)
18.7 MJ/kg (low heat value)
Hardwood (air-dry, 16% moist) 16.8 MJ/kg (high heat value)
14.6 MJ/kg (low heat value)
Hardwood (green, 50% moist) 10 MJ/kg (high heat value)
8.3 MJ/kg (low heat value)
Softwood (oven-dry) 21 MJ/kg (high heat value)
Softwood (air-dry, 20% moist) 16.8 MJ/kg (high heat value)
Softwood (green, 50% moist) 10.5 MJ/kg (high heat value)
Bark (oven-dry) 20 MJ/kg

Note: Variation of ± 10% occurs within and between wood species

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