Feasibility study of ground source energy systems

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Courtesy of ESI Ltd - Environment Specialists

Client: Shaftesbury Estates

Location: Wimborne St Giles, Dorset

Services: Feasibility Study

Summary: Feasibility Study for renewable energy options demonstrated that ground source energy should be used for cost effective space heating in a historic building

As part of the restoration of St Giles House, Shaftesbury Estates intends to use sustainable energy for heating the building.  ESI were commissioned to provide a feasibility study of the renewable energy options for the scheme, focussing on ground source energy. The St Giles estate has the benefit of several options for ground source energy: a continuously flowing leat, a large ornamental lake, large open areas and it is built upon Chalk aquifer which is an excellent source of groundwater.  Energy for space heating could be obtained from any of these sources.

Once we had confirmed that they had the capacity to meet the building energy demand, it was clear that a surface water energy source would be the preferred option, due to the significantly reduced capital costs. We therefore considered, in detail:

1) An open loop system that passed water from the leat through a heat exchanger, and,

2) A closed loop system that circulated refrigerant through an array of closed loop geothermal heat exchange pipes installed in the ornamental lake.

Key considerations were local environmental factors, including the stability of flow and temperature in the leat and lake (the water is taken from the River Allen which is a Chalk-fed groundwater stream). These suggested that both options were sustainable and would lead to no derogation of habitat for downstream ecosystems or for water resources. 

The closed loop system in the lake was ultimately the preferable option due to lower capital costs. Direct use of water from the leat would have required secondary plate heat exchangers to deal with turbidity in the surface water, as the leat is open over part of the reach between the River Allen and St Giles House. The preferred option is now being installed in the lake by our partners, ISOEnergy Ltd.

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