Carbon-neutral heating for Sudbury Hall

Monday, 16 February 2009

Wood pellet biomass boilers for the National Trust

As part of its drive to reduce carbon emissions across its estate, the National Trust has replaced two oil-fired boilers at Sudbury Hall in Derbyshire with wood pellet biomass boilers manufactured by Hoval. The project presented significant logistical, technical and project management challenges, which were overcome through strong teamwork between all parties.

Sudbury Hall is a Grade I listed 17^th Century family home that features richly decorated interiors and is also home to the Museum of Childhood, with displays about childhood from the 19^th Century onwards. Many of its exhibits are sensitive to changes in temperature and humidity so a responsive and reliable space heating system is critical to protecting these assets.

Following a feasibility study by Lorien Engineering Solutions, Project Manager and Engineering Consultant throughout the project - as well as visits to local Hoval installations - carbon-neutral biomass boilers were identified as the best replacement for the existing, ageing oil boilers.

"The National Trust is committed to installing renewable energy technologies in its properties wherever appropriate," explained Charles Robinson, the National Trust's senior building surveyor. "The fact that we were able to source both the boilers and wood pellets locally also helped to reduce the project's carbon footprint," he continued.

"The choice of wood pellets, rather than chips, was dictated by a number of factors. These included the higher density and calorific value of wood pellets and the available space for fuel storage," added Lorien's Nick Fox.

Before the 2 x 150kW STU boilers and pellet hopper could be installed in the designated cellar space, it was necessary to remove the existing oil boilers and oil tank. Working closely with installer Instatherm, which also supplied the pellet feed system and underfeed stokers, Hoval took a turnkey role in managing these works, through to the commissioning of the new boilers.

A significant complication was the fact that the 12,000 litre oil tank had been built in-situ and could not be removed intact through existing doorways. Consequently, this had to be emptied and dismantled prior to removal. As no hot works were permitted in the vicinity of the tank this was carried out using cold cutting techniques. In addition, no noisy works were allowed between the hours of 10am and 5pm, when the building is open to the public, so the work was carried out within clearly defined windows.

Sudbury Hall's listed status also meant that no alterations to the external fabric were allowed. "This presented us with a challenge in getting the boilers to the cellars," explained Hoval's Robert Hollingworth. "Having considered various options we decided to use a crane to lift the boilers over the building to an inner courtyard and manhandle them through underground passages to the cellars. The lift, by local crane company Hutchinson Engineering Services, had to be carried out very quickly to avoid disturbance to visitors," he added.

In its role as Principal Contractor, Lorien was also responsible for managing Health & Safety during the project. "Health and safety issues were given a very high priority during the project because of the lifting works and the basement location of the installation. There were also members of the public close to the site for much of the time," recalled Nick Fox.

The pellet hopper, located adjacent to the boilers, is manufactured from a special fabric, mounted on a steel frame - so it could be easily assembled in the cellar. The fabric is designed to allow air to pass through while retaining dust, so the hopper does not need to be vented during filling. The pellets are sourced from local biomass fuel specialist Strawsons Energy.

Another benefit of using wood pellets was the ability to construct a flexible feed system. "The siting of the hopper in relation to the boilers meant that the feed system needed to be routed around obstacles, which is very easy to do when using pellets," recalled Instatherm's Lawrence Dixon. "In contrast, with wood chips we would have been confined to straight runs and 90 degree bends," he continued.

Lawrence Dixon also points out the importance of good communications with the client from the start of the project. "Most people have no experience of solid fuel boilers and, while modern biomass boilers are very easy to use, different procedures are involved. For that reason we explained the details to the staff before the project began so they would fully conversant with routines, such as removing ash every fortnight or so, once the boilers were handed over".

Despite its complexity, the project was completed within a six week period. "We are very pleased with the outcome and received an excellent service from Lorien, Hoval and Instatherm throughout the project. In fact, our staff at Sudbury Hall are so pleased with the support they've received that they've named the boilers Lawrence and Colin after our main contacts on the project," Charles Robinson concluded. 

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