Why wood works
June 1st 2008

As 'renewable theory' is being put into practice it's clear that biomass is proving particularly popular and practical. Ian Dagley of Hoval explains why

Now that renewable energy sources are being included in many more projects,a clearer picture is emerging of how the theories are best put into practice.

Every project has its own particular requirements, of course, but there are some definite trends developing.

In the case of space heating and hot water, biomass boilers are proving particularly popular – on their own or integrated with other renewables and with conventional heating technologies.Here, the key to 'mixing and matching' different technologies is a high level of predictability and controllability.

For that reason, carbon-neutral wood pellets are often the favoured form of wood fuel because they comply with international standards for size and moisture content, which makes their combustion characteristics very consistent. Less consistent fuels, such as wood pellets, require complex control systems to compensate.However,where there is a plentiful supply of wood very close to the building,wood chips may be the most suitable fuel option.

In considering biomass, it's important to realise how modern biomass boilers differ from older wood-burning boilers.Modern wood burning boilers now offer efficiencies of over 90%, compared to around 50% for older models.They are also much easier to use, with features such as full automation of operation, function control and fuel dosage.

At the new 2884m2 Newark Beacon business innovation centre, for example, two Hoval BioLyt wood pellet boilers have been installed to meet most of the space heating and hot water requirements – backed by an Ultragas condensing boiler for peak demands.

Here,wood pellets from a 20 tonne storage silo are fed to the boilers by an automatic pellet feeding system.The boilers are set up in a 'lead and lag' configuration, responding to varying heat demands by switching off when not needed and re-igniting automatically when heat demand increases.

Maintenance is also minimal, as the BioLyt boilers also feature selfcleaning heating surfaces to avoid soot deposits and maintain heat exchange efficiency.Ash is removed automatically to a container which, on average, requires emptying once or twice per heating season and can be used as a fertiliser on the surrounding grounds.

In other projects optimum performance may come from combining the strengths of different types of boilers. For example, the wood boilers could provide the heating for domestic hot water, while a condensing boiler exploits the lower return temperatures of the space heating system to maximise condensing.

In all cases, one important consideration is the need for storage of the fuel and the benefit of practical experience in making adequate provision for all aspects, including deliveries.A major advantage of wood pellets is they can be delivered by a 'blower' lorry into a storage silo which, for instance, might occupy the same space as previous oil storage tank.

In some areas, biomass boilers may replace old coal-fired boilers – in which case there is only a little work required to convert coal storage for wood storage.

Often, projects using biomass also incorporate other renewables, such as solar water heating.As solar heating projects require auxiliary heating as back up, using biomass boilers can be an ideal choice.The key in this type of project is to ensure that the control system is able to cope with a mix of solar, biomass and any other renewables – such as heat pumps – quite possibly integrating them with conventional heating technologies as well.

Here, use of innovative storage vessels that can accommodate feeds from different heat sources in a controlled fashion are proving invaluable in making the most of the options available.Within the vessel are two coils for connection to different heat sources, plus a stainless steel sphere for domestic hot water which is heated by the surrounding hot water in the vessel and can be topped up with an immersion heater if necessary.

For all of these reasons it makes perfect sense to seek advice from companies that have experience in all of these technologies and in getting them to work together to deliver maximum benefits.

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