Case study

Blervie House, Moray

205kW woodchip boiler

Key facts

Commisioned

September 2015

Scheme

Heating for a large country house with integral staff accommodation.

Boiler and plant

205kW woodchip boiler with 5,000 litre accumulator tank and 4m diameter agitator / auger fuel feed. The plant room and fuel store are housed in a new timber building about 100m from the house. The system is supported by a 100kW back-up oil boiler.

Fuel

The boiler is expected to use around 100 tonnes of wood chip to produce 290MWh of heat per annum.

Chip storage

A new agricultural shed has been constructed adjacent to the plant room to act as a bulk chip store. Chips are transferred from the bulk store into the hopper using a tractor with front loader.

Grant / Funding

The project was self-funded and is fully accredited on the non-domestic RHI scheme.

Savings / Investments

Income from the RHI and fuel cost savings are expected to result in a return on investment exceeding 15%.

CO2 saving

More than 90 tonnes per annum compared to a modern oil fired system.

Blervie House was heated by over 100 electric night storage radiators resulting in fuel bills exceeding £1,000 per month even in summer. As part of a renovation project, Dunster was approached to design an integrated, multi-zone heating and hot water system to allow the house to be heated effectively and affordably for the first time in its history.

To minimise the impact on the listed building, and to keep chip handling machinery away from the house, the boiler and associated plant were installed in a new timber building approximately 100m from the house. This was connected to the house by buried, pre-insulated district heating pipe. Within the house, state of the art controls provide weather compensated heating and ensure that it is a simple matter to adjust temperatures to match the demands of variable occupancy. Although still part of the networked system, the housekeeper’s flat has been set up with its own controls and heat meter so that the occupant can have complete control of heating and hot water timings and temperatures.


Blervie House

Fuel supply and chip handling

The chip hopper forms an integral part of the building which holds the biomass boiler and associated plant. It is loaded from the adjacent bulk chip store using a tractor and bucket and can hold enough fuel for around 3–4 weeks heating in winter and around double that in summer. Initially, wood chips were bought from a local supplier but estate timber is being seasoned and, once dry, will be chipped directly into the bulk store by a contractor.

System design and installation

Dunster worked with the client’s M&E consultant to specify the main heating plant and ensure that the new radiator and hot water systems installed in the building operated seamlessly with the biomass boiler to maintain maximum efficiency and minimise losses in the external pipework. The 5,000 litre thermal store allows the biomass boiler to operate at peak efficiency even when demand is low in the summer whilst the 100kW oil boiler, which was installed as a back-up system, has not been required in the first year of operation.

Benefits

In addition to the CO2 savings and a return on investment of over 15%, the low cost of heat and the sophisticated controls allow unoccupied areas of the house to be provided with background heating which greatly benefits the fabric of the building and improves habitability. By using a wood chip fuelled system, costs are kept to a minimum and there is also an economic incentive to actively manage the estate woodlands which has much wider environmental benefits. The client particularly appreciates the ability to monitor and adjust all elements of the heating system using his mobile phone and has been impressed by the simplicity and cleanliness of its operation.

Download the Blervie House case study

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