Case study

Innes House, Morayshire

195kW Woodchip District Heating System

Key facts

Commisioned

January 2013

Scheme

Supply of hot water and heating to a
Scottish Mansion House and three flats.

Boiler and plant

A 195kW ETA Hack woodchip boiler with a 5,000 litre accumulator tank and a 5.5m diameter agitator and auger fuel feed system. Properties are connected via a 230m network of district heating.

Fuel

The boiler is expected to use approximately 130 tonnes of G50 wood chip per year to produce around 340,000MWh of heat.  

Chip storage

A redundant dutch barn on the estate was renovated to provide storage for a year’s supply of woodchip, as well as space for chipping operations and bulk timber storage. Chips are transferred to the boiler in an agricultural trailer as required.

Grant / Funding

The system was funded by the estate and is RHI accredited.

Savings / Investments

Prior to the installation, the house was spending over £20k per annum on oil. The cost of purchasing and chipping the first year’s biomass supply was less than £7k which is expected to fall as more ‘home produced’ timber is used. Combined with annual RHI income of c. £22k, the investment will be paid off in under 5 years.

CO2 saving

Estimated at 120 tonnes per annum.

Innes House is a large private house in the north of Scotland used for weddings and corporate entertainment. The ever rising cost of oil heating and a wish to maximise estate self-sufficiency drove the decision to invest in a biomass heating system.

The boiler and associated plant was installed in an extension to the stable block with a redundant storage room converted into a chip hopper. Dunster worked with the estate to design a system that minimised the impact on the listed buildings whilst ensuring maximum flexibility in fuel supply. Due to their proximity, it was decided to include three flats to provide lower cost heating to the tenants.

Fuel supply and chip handling

The first year’s supply of fuel was bought as bulk seasoned timber and chipped by a contractor into a bulk storage barn. Subsequent year’s supplies are being bought as bulk, freshly cut timber and seasoned on site. As estate woodlands are brought back into active management, these will ultimately be used to supply all the timber required to run the system. Chip is transferred from the bulk store in an agricultural trailer and is tipped into the trough of the ‘fast fill’ system which uses powerful augers and a ‘throw’ mechanism to load it into the fuel store at high level. Although the store holds around 3 weeks’ worth of chip at winter consumption rates, it is found most convenient to transfer about one 20m³ trailer’s worth each week as this fits in neatly with other tasks.

 

 Innes House installation

System design and installation

As the 280kW peak heat requirement of the house and flats significantly exceeds the 195kW capacity of the system, the main house boilers have been retained to provide peak-load capacity. Should demand exceed capacity, the oil boilers will fire up to ensure sufficient heat supply to all properties. Dunster’s system design forecast that biomass would supply 90% of the heat requirement with the balance of 10% being delivered by oil. However, by adjusting the way the house is heated to prevent spikes in demand, initial indications suggest that the oil boilers are not being used at all.

Benefits

In addition to dramatically reducing the heating bills, the project has been the catalyst for regenerating forestry capacity on the estate.

Download Innes House case study

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