Biomass boiler will save sustainability-conscious charity £1.6 million

Project overview

Dartington Hall, the largest medieval house in the west of England, is part of a 1,200-acre estate which belongs to a registered Social Enterprise charity with special interests in the arts, social justice and sustainability. The Dartington Hall Trust uses the Grade I listed hall and neighbouring medieval courtyard buildings as a conference centre, wedding venue and guest accommodation. In providing space heating and hot water for the courtyard buildings,
two ageing 600 kW oil boilers in the courtyard boiler house were consuming 600 to 700 litres of oil per day. The Trust wanted to replace these with a system that would be more environmentally friendly and less expensive to run.

The Viessmann solution

With sustainability so important, and with the Hall’s rural location near Totnes in Devon placing it off the gas network, the Trust’s preferred alternative to oil-fuelled heating was a wood-fuelled biomass boiler. Wood is a home-grown energy source, transported using a
minimum amount of energy. It contributes to local economies and is a CO₂neutral fuel, releasing only as much CO₂when it is burned as the trees have absorbed. And because the wood harvested from sustainable forestry is renewable, biomass is eligible for significant
payments from the government’s Renewable Heat Incentive (RHI) scheme.

After evaluating biomass options, consultants Mole Valley Renewables advised the Trust to install a 950 kW Viessmann Pyrotec boiler fuelled by wood chip. The Pyrotec range of boilers can also be fuelled by wood briquettes, shavings or pellets (with a maximum water content of 50%). To accommodate the boiler, a farm building next to the Visitor Centre was renovated and turned into a new showcase energy centre. This has viewing windows to allow visitors to witness firsthand the biomass system in operation, with visitorfriendly
information explaining how the system works. Dartington Hall’s project manager, Richard Williams, said: “We’re working to promote agro forestry and woodland management on the estate, including a biomass fuel trial with the Forestry Commission. This will give us the potential to provide a significant amount of the wood chip for our biomass from the estate itself.”

Installed by Aston Cord Energy Services, the Pyrotec 950 is easy to maintain, with fully automatic ash removal, an optional pneumatic cleaning system and a flue gas scrubber. A ‘walking floor’ system ensures a constant supply of chip wood to an underfeed stoker with a downward external grate and moving burnout grate for optimum combustion. A precise oxygen sensor controls primary and secondary combustion air for an exceptionally high fuel-to-heat conversion efficiency of up to 92%.

Advanced combustion technology makes possible ultralow CO₂ particulate and NOx emissions. An automatic ignition device (for fuels with water content of less than 40%) limits idling and saves fuel and a classic triple-pass heat exchanger ensures maximum heat transfer and efficiency.

The Pyrotec boiler is coupled to a 15,000-litre buffer vessel, which serves as an energy store. This accumulator tank absorbs heat when it is not required and releases stored hot water into the system when the buffer gets up to temperature to provide space heating and domestic hot water.

Big reductions in costs and emissions

Viessmann’s Pyrotec biomass boiler has helped the Dartington Hall Trust satisfy one of its core values, sustainability, by lowering its energy consumption and emissions. Replacing the two 600 kW oil-fuelled boilers with one 950 kW biomass boiler has resulted in the same space and water heating demands being met with a reduction in carbon dioxide emissions of 400 tonnes every year.

The switch to biomass has also enabled the Trust to make significant financial savings, through a combination of lower fuel costs and RHI payments, of £80,000 per year. The RHI payments alone will total, during the 20 years the boiler is eligible, to a massive £1,600,000.

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