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September 20101
Wood to Warmth – Biomass Fuels and Heat Energy Calculations
Michael Beech
TV Energy
September 20102
Biomass Fuels
As general guide, the energy available fromdifferent biomass fuels can be summarised asfollows:
• Logs Seasoned to 20%MC, 4100kWh/tonne, 1900kWh/m3 (hardwood, stacked), 1400kWh/m3 (softwood,stacked)
• Pellets <10%MC, 4700kWh/tonne, 2800kWh/m3 minimum
• Chips 30%MC, 3300kWh/tonne, 950kWh/m3 (hardwood), 720kWh/m3(softwood)
September 20103
Biomass Fuels
CV hardwood (broadleaves) = CV softwood (eg. pine, SRC)Higher growth rate of softwood offset by its lower energy density
September 20104
Biomass Fuels
Moisture content, energy, density comparisons
Moisture content
Wood Net CV MWh/t
Hardwood density kg/m3
Softwood density kg/m3
Hardwood chip energy
density
Softwood chip energy
density
Hardwood chip bulk density
Softwood chip bulk density
% MWh/t kg/m3 kg/m3 MWh/m3 MWh/m3 t/m3 t/m30% 5.28 550 410 1.08 0.80 0.204 0.1525% 4.98 579 432 1.07 0.80 0.214 0.16010% 4.68 611 456 1.06 0.79 0.226 0.16915% 4.38 647 482 1.05 0.78 0.240 0.17920% 4.09 688 513 1.04 0.78 0.255 0.19025% 3.79 733 547 1.03 0.77 0.272 0.20230% 3.49 786 586 1.02 0.76 0.291 0.21735% 3.19 846 631 1.00 0.75 0.313 0.23440% 2.90 917 683 0.98 0.73 0.340 0.25345% 2.60 1000 745 0.96 0.72 0.370 0.27650% 2.30 1100 820 0.94 0.70 0.407 0.30455% 2.00 1222 911 0.91 0.68 0.453 0.33760% 1.70 1375 1025 0.87 0.65 0.509 0.38065% 1.41 1571 1171 0.82 0.61 0.582 0.434
September 20105
Biomass Fuels - Costs
Fuelp/kWh
fuel
Heating system
seasonal efficiency
p/kWh heat
Woodchip 30%MC (estate supplied) £60 /tonne 1.82 85% 2.1Woodchip 30%MC (external supplied) £80 /tonne 2.42 85% 2.9Woodchip 30%MC (external supplied) £100 /tonne 3.03 85% 3.6Wood pellets (bulk, 10tonnes, 15miles delivery) £175 /tonne 3.65 85% 4.3Wood pellets (bagged, 1tonne, 15miles delivery) £260 /tonne 5.42 85% 6.4Hardwood logs 25%MC (bulk, 1cu.m) £95 /cu.m 5.55 80% 6.9Heating oil (Class C 28s kerosene) 50 p/litre 4.85 75% 6.5Heating oil (Class C 28s kerosene) 50 p/litre 4.85 88% 5.5Heating oil (Class C 28s kerosene) 55 p/litre 5.34 75% 7.1Heating oil (Class C 28s kerosene) 55 p/litre 5.34 88% 6.1Heating oil (Class C 28s kerosene) 60 p/litre 5.83 75% 7.8Heating oil (Class C 28s kerosene) 60 p/litre 5.83 88% 6.6Natural gas (commercial rate) 2.5 p/kWh 2.50 75% 3.3Natural gas (commercial rate) 2.5 p/kWh 2.50 88% 2.8Natural gas (domestic rate) 4.0 p/kWh 4.00 75% 5.3Natural gas (domestic rate) 4.0 p/kWh 4.00 88% 4.5LPG 50 p/litre 6.68 75% 8.9LPG 50 p/litre 6.68 88% 7.6Electricity (night rate) 5.0 p/kWh 5.00 100% 5.0Electricity, ground source heat pump (night rate) 5.0 p/kWh 5.00 350% 1.4Electricity, air source heat pump (night rate) 5.0 p/kWh 5.00 250% 2.0Electricity (day rate) 14.0 p/kWh 14.00 100% 14.0Electricity, ground source heat pump (day rate) 14.0 p/kWh 14.00 350% 4.0Electricity, air source heat pump (day rate) 14.0 p/kWh 14.00 250% 5.6
Unit Cost (ex VAT)
September 20106
Heat Energy Calculations
Calculating heat load & woodfuel use
Fuel bills (existing build) -> kWh i/p -> system efficiency ->
kWh o/p -> % from biomass boiler -> biomass efficiency ->
Biomass fuel kWh -> biomass fuel kWh/tonne -> tonnes/m3
• System efficiency – old boilers, EE improvements possible?• Biomass boiler heat >90% of annual heat load ideally• Biomass efficiency – losses during start up, thru’ buffer tank
For new build, need to know the calculated annual heat demandto determine woodfuel use
September 20107
Heat Energy Calculations
Heat loads – Mixed commercial/ domestic
Winter
Summer
September 20108
Heat Energy Calculations
Heat load variation - seasonal
January June/ July December
September 20109
Heat Energy Calculations
Biomass and conventional boilers - winter
Heat outputs. 150kW biomass boiler, 350kW oil boiler
Buffer tank activity. 5000litre, 20deg.C deltaT
September 201010
Heat Energy Calculations
Biomass boiler - summer
Heat output
Buffer tank activity
September 201011
Heat Energy Calculations
Summer heat supply – alternative options
• Additional smaller o/p biomass boiler – higher capital cost, available space, central heat losses vs. heat use, cost/ benefit, flexibility
• Conventional boiler – convenience, use existing? energy costs / CO2 emissions
• Electric immersion heating – convenience, low capital cost, highest operating cost/ CO2 emissions, night rate option?
• Solar thermal system – capital cost, space requirements, orientation, lowest operating cost/ CO2 emissions, size carefully, cost/ benefit vs. biomass fuel use
