An explanation of terms associated with Wood Energy
An Archimedes screw used to transfer fuel or ash in a wood boiler.
Biomass can be defined as the biodegradable fraction of products, wastes and residues from agricultural, forestry and related industries, as well as the biodegradable fraction of industrial and municipal waste. There is no common definition of biomass fuels, but the following list summarises the main sources16:
• Cereal and agricultural crops (straw/Oilseed Rape/sugar beet etc)
• Spent cooking oils
• Animal slurries
• Solid municipal waste and refuse derived fuels
• Industrial and commercial wastes (particularly from the food sectors)
Biomass energy specifically refers to the conversion of these fuels for heat, heat and power and transport fuels.
A mechanical device attached to a fuel silo or delivery vehicle that is capable of blowing wood fuel into an above ground silo.
Also known as a thermal store or an accumulator tank. Used to store hot water produced by a boiler before it is circulated as heating or domestic hot water.
A mechanical device attached to a fuel silo that is capable of conveyng wood fuel into an above ground silo.
A network of insulated underground flow and return pipes connected to numerous individual buildings supplied with hot water from a central boiler plant. Hot water use is usually metered at each building.
Biomass fuels produced from purpose grown agricultural crops such as sugar beet, straw and fast growing willow coppice.
A storage container used to store wood fuel before it is automatically transferred into the boiler for combustion.
A gigajoule (GJ) is a metric term used for measuring energy use. One GJ is equal to:
• 277.8 kWh of electricity
• 26.9 m3 of natural gas
• 25.9 litres of heating oil
So for example, one tonne of wood chips at 40% moisture content contains 10.54GJ of energy.
A system of hot water pipes mounted above the boiler combustion chamber that uses the combustion gases thermal energy to create hot water.
A small electronic device to measure and record the amount of heat energy a boiler has produced based upon flow volumes and return temperature. The output is shown in kWh or MWh.
kW or MW hours
One watt-hour is the amount of energy expended by a one-watt load (e.g. light bulb) drawing power for one hour. For example a 100W light bulb (0.1kW) left on for 10 hours per day will consume 1 kilowatt-hour per day (0.1kW x 10h).
The table below shows the most common multiples and terms:
So for example, 1 tonne of wood chips at 40% moisture content contains 2,929kWh of energy or 2.93MWh of energy.
The average load of heat required by a building over a 12 month period. The mean load will be much lower than the peak load. Mean and peak loads are expressed numerically in kW’s or MW’s.
Oven Dried Tonne (ODT)
As wood chips can be produced and supplied to differing moisture contents it is usual to purchase fuel in ODT’s. This means that wood fuel can be purchased according to its energy content. For example 1 tonne of wood chips at 50% moisture content contains much less energy than 1 tonne of wood chips at 30% moisture content. Therefore to provide equal amounts of energy, wetter wood fuels must be used in greater quantity. Purchasers of fuel therefore agree to a price based upon the weight of fuel as if it was being supplied bone dry—although of course in practice it will be delivered and used with a percentage of moisture in it.
The maximum load of heat required by a building (usually in winter and with high occupancy) or the maximum output of a boiler. The peak load will be much greater than the mean load. Mean and peak loads are expressed numerically in kW’s or MW’s. Wood boilers are not normally sized on the peak load. Buffer tanks or back up boilers are used to meet peak loads.
Subterranean fuel silo
An underground storage container used to store wood fuel before it is automatically transferred into the boiler for combustion. Allows fuel to be simply tipped when delivered in lorries.
A system of pipes and radiators to provide space heating in buildings.
A subset of biomass energy. Across the EU 85% of the biomass market is supplied with solid wood biomass—this is about 100 million tonnes of wood.17 There are four possible sources of solid wood biomass fuel:
• Co-products of sawmill industry
• Post consumer wood waste
• Purpose grown energy crops