DESCRIPTION

Biomass can be burnt directly to provide heat in buildings. Wood from forests, urban tree pruning, farmed coppices or farm and factory waste, is the most common fuel and nowadays is used commercially in the form of wood chips or pellets, although traditional logs are also used.

There are two methods of using biomass heating in housing, single room heaters or stoves, and boilers, with biomass replacing gas or oil. Both systems can be designed to burn smokelessly to comply with the Clean Air Acts. Boilers can be fed automatically by screw drives from fuel hoppers. Electric firing and automatic de-ashing are also available.

For non-domestic applications, biomass boilers replace conventional fossil fuel boilers and come with the automated features mentioned above. Fuels other than wood, such as straw can also be used.

Biomass is normally considered a carbon neutral fuel, as the carbon dioxide emitted on burning has been (relatively) recently absorbed from the atmosphere by photosynthesis and no fossil fuel is involved. The wood is seen as a by-product of other industries and the small quantity of energy for drying, sawing, pelleting and delivery are discounted.

Biomass from coppicing is likely to have some external energy inputs, for fertiliser, cutting, drying etc. and these may need to be considered in the future.

WHERE CAN BIOMASS HEATING BE USED?

Biomass heating is theoretically applicable to any building requiring heat; however practical constraints suggest that it is currently most applicable to lower density situations due to fuel supply and storage issues. The most common application of biomass is as one or more boilers in a sequenced (multi-boiler) installation where there is a communal i.e. block or district heating system. There must be a local and adequate supply of appropriate biomass fuel (normally wood chips or
pellets) and room for delivery and storage. For individual houses, room stoves or central heating boilers are available but with the same constraints relating to fuel supply. Biomass boilers replace conventional boilers and have no aesthetic impact.

COST RANGES

The additional capital costs of biomass boiler systems, including fuel storage and automatic feeding, range from around £2,000 for a single house, to £30,000 to supply 33% of the heating for a standard office of 3,000m2. Biomass fuels, unlike other renewable fuel sources, will have to be bought unless they are obtained as waste material from another organisation. Prices vary depending on the type and distance for delivery and may be similar to other solid fuels.

OUTPUT RANGES

Biomass boilers are available in most size ranges, from individual houses to commercial installations.

TECHNICAL FEASIBILITY ISSUES OR CONSTRAINTS

Issues to be considered with biomass heating are fuel availability, delivery and storage, and the need to commission the boilers and service them at regular intervals. For these reasons, biomass heating can be more applicable to lower density areas. However, these issues can be overcome by considering biomass as a fuel option early in the design process so that storage/delivery facilities can be factored in. There is also considerable waste wood arising from forestry operations that could potentially be used. River transport of fuel could be considered to prevent increased road deliveries to a site.

Arrangements for ash disposal and de-coking must be made. For individual domestic use of biomass boilers, and even more so room stoves, the house occupants need to be willing and capable of managing fuel supply, ash removal and disposal. Domestic biomass boilers require considerably more space than a conventional boiler and cannot normally be located in a standard modern kitchen.

MAINTENANCE REQUIREMENTS

Biomass boilers require more frequent cleaning than gas or oil boilers and they must be capable of being taken out of service for cooling and cleaning while maintaining the building heating supply, particularly in communal and non-domestic heating systems.

ADDITIONAL BENEFITS OF TECHNOLOGY

It is unlikely that any cost savings will arise from the use of biomass boilers as the fuel is likely to be comparable in cost to other fuels, if not more expensive.

PLANNING AND LEGISLATIVE ISSUES

The combustion gases will require an external flue usually terminating above the ridge line of the building. This part of the system will be visible and should be designed to be as unobtrusive as possible. Planning permission may be required.

LINKS TO SOURCES OF MORE DETAILED TECHNICAL INFORMATION

• Companion Guide to PPS 22: The technical annexes, available at
www.odpm.gov.uk/planning.

• The Official Guide to Approved Solid Fuel Products and Services 2003/2004. HETAS Ltd.
www.hetas.co.uk/.

• The British BioGen Code of Practice for Biofuel Pellet Burning Roomheaters <15kW. British Biogen 2001, available at www.britishbiogen.co.uk.
This site also contains other useful information.

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