How Biomass Works

Burning biomass does release CO2, but only the amount it absorbed while growing and is therefore considered to be a carbon neutral process.

There are some CO2 emissions associated with transporting the biomass fuel to your home. Fuel from a good local supplier is often more convenient, and minimises these transport emissions.

Different technologies

Essentially, there are two ways in which biomasstechnology can provide heat for a home. A biomass boiler can replace the conventional boiler in a wet heating system, providing heat and hot water for the whole home. A biomass stove acts as a single room heater, sometimes with a back boiler to provide hot water.
All boilers and stoves require a flue, which can be fitted inside an existing chimney. This must be highly insulated to prevent condensation of flue gases.

The three main fuels which can be used with a fuel system are wood logs, wood pellets and wood chips.

Storing the heat produced eg as hot water, for later use with a thermal storage device can improve the efficiency of a biomass system.

Biomass boilers

Pellet boilers

• Typically consist of a boiler unit and separate pellet store, and range from 5-50kW.

Pellets

• Generally fed automatically straight from store/silo into boiler, allowing flexibility in distance between boiler and store.
• Can be stored indoors or outdoors in smaller tanks (approx 1 week supply), or larger silos/underground tanks/fabric bag system to allow longer times between fuel deliveries (up to a year supply).
• Can be blown pneumatically directly into the store (no handling required but requires vehicle access) or supplied in bags to be poured manually into the store (can be dusty).

Log boilers

• Typically range from 5-50kW, generally cheaper than wood/chip boilers.
• Need to be loaded with fuel by hand every 1-3 days (although this depends on numerous factors), which takes 10-15 mins. This requires ready access and can involve a certain amount of dust/dirt.
• Achieve the best efficiency by fitting a log boiler with an accumulator/buffer tank to store heat as high temperature hot water, which is then used for heating and hot water as and when required.

Combination boilers

• Not to be confused with a gas or oil combination boilers.
• These have adjustable control settings which allow them to burn more than one type of fuel.

Biomass stoves

• Both log and pellet stoves are available – pellet stoves provide automatic metering and feeding of pellets from an integrated storage space, while log stoves are generally loaded by hand.
• Efficiencies range from 60-90% – typically 70%.
• Higher output stoves can be used with a back boiler to provide hot water as well as heating.
• Ideal for refurbishing older buildings with functioning chimney as cheaper alternative to installing central heating.
• Generally lit by electronic ignition.
• Typical cost around £3,7001, may be higher for higher output systems used with back burners.

Thermal storage devices

• Integrated heat storage (accumulator) tank
• The boiler or stove heats water to around 90º in a highly insulated tank, rather than directly providing heating. This can then be drawn off for heating and hot water as required.
• Increases efficiency of the system as the boiler or stove doesn’t have to be turned down to lower (and less efficient) settings to match heating demand.
• Also, can be used to integrate solar water heating to back up the system during peak demand, and provide hot water during the summer months.
• Stand-alone ceramic heated
• Ceramic material absorbs heat from the burning fuel and releases it into the room over a long period of time – a 2-hour burning period can provide heat for up to 24 hours.
• Heat output cannot be adjusted.

Compliance

• All boiler and stove installations must comply with safety and building regulations.
• Smokeless zones: ‘exempted’ appliances required if live in a ‘smoke control zone’. See www.uksmokecontrolareas.co.uk for further advice.
• Planning: If the building is listed or in an area of outstanding natural beauty (AONB), then customer will need to check with their local council’s planning department before a flue is fitted.
• We recommend that an accredited installer / HETAS (www.hetas.org.uk) registered competent person is sought. If a HETAS registered competent person is not used, customer should contact building control department of their local council to check the installation.

Further in depth information about Biomass systems and more can be found at www.resintegration.co.uk

Savings potential of Biomass