Case study

Alvie Manse, Inverness-Shire

35 kW Wood Chip Heating System

Key facts

Commissioned

February 2011

Scheme

Supply of hot water and heating to 6 bedroom domestic dwelling on the Alvie Estate, Inverness-Shire.

Boiler and plant

35 kW ETA Hack woodchip boiler installed in a converted outbuilding with a 2,000 litre accumulator tank.

Fuel

The boiler is expected to use approximately 90m³ of G30/50 woodchip per annum, producing around 100,000 kWh of heat. Seasoned woodchip fuel is produced by the estate.

Chip storage

A 20m3 fuel store was dug into the ground adjacent to an existing listed outbuilding which was used as the boiler house.  Woodchip is transferred direct from this to the boiler by auger and rotary arm agitator.  Refilling of the fuel store is achieved by tipping trailer approximately every 2 months.

Grant / Funding

The system was directly funded by the estate. However, as it is intended to convert the building into a guest house, it is intended to apply for the non-domestic RHI once applications open in November 2011.

Savings / Investments

The previous oil heating system had become so expensive to run that it was barely used prior to this installation so comparative costs are not available. However annual woodchip bills are now expected to be in the region of £2,000.

CO2 saving

Estimated at 30 tonnes per annum.

Alvie Manse is a substantial (6 bedroom plus flat), listed, period house for which the cost of oil heating had become prohibitive. As a result of this, and as part of an overall strategy to increase the use of renewable energy on the estate, it was decided to install a woodchip system for space heating and domestic hot water.

The existing oil fired boiler was removed as experience with other schemes on the estate had given them sufficient confidence that no backup system would be required. Since it is a single domestic dwelling, the scheme does not qualify for support under the current RHI, however, it is expected to qualify when it is converted into a guest house in the future.

Fuel supply and chip handling

Woodchip is delivered from the estate’s existing woodchip supply business by standard tipping trailer directly into the feed hopper. This was dug into the ground adjacent to an existing outbuilding which houses the boiler and accumulator tank. The proximity of supply means that no bulk store is required and refilling occurs at approximately 2 monthly intervals. Due to the size of the supply business, timber for chipping is sourced both from the estate and through the open market. It is stored outside for around 12-18 months before chipping to ensure a moisture content of below 30%.

Wood chip store and biomass boiler

System design and installation

The system was designed for 100% of heat and hot water to be provided by Biomass. A 2,000 litre accumulator tank was installed to assist with peak heating loads and to avoid inefficient short cycling of the boiler.

Wood chip boiler, thermal store and wood chip store

Benefits

This project has substantially reduced the heating bills for the house as well as contributing to the estate’s policy of energy self-sufficiency.

Recent Dunster case studies

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St Paul’s Church, Weston-Super-Mare – Containerised 140kW wood pellet heating system

Alvie Manse, Inverness-Shire – 35 kW Wood Chip Heating System

St Audries Bay Holiday Club – 130 kW Wood Chip Heating System

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