Ground Source Energy Support for Mechanical and Engineering Contractors
A well designed and correctly installed Ground Source Energy system is usually a cost effective and low carbon solution to a building’s energy requirements. If a building’s energy demand or ground properties are not clearly defined prior to a scheme being designed, a conservative system design is likely to be developed which normally leads to a more expensive installation. lt will be a less energy efficient solution. An inefficient Ground Source Energy scheme is expensive and is of little value.
An integrated approach to a Geothermal system combining the detailed energy demand of the building, heat pump selection and ground loop design is required. The most efficient schemes with the lowest cost to install occur when the energy demand is well defined and where a balance between heating and cooling loads can be taken into account.
Site specific information gained from an accurate geological assessment of the ground properties conducted by ESI allows a more precise design of the ground loop, leading to optimised performance and reduced installation costs.
ESI provides a range of technical design services to help and support contractors to achieve an integrated and efficient building heating and cooling solution.
For smaller closed loop systems, simpler design tools including EED Earth Energy Designer are appropriate for modelling the performance of regular arrays of homogeneous Borehole Heat Exchangers (BHEs). This simplified approach does not take into account the benefits that could be obtained from groundwater conditions and does not account for detail of the geological sequence.
On larger closed loop schemes, conservative assumptive designs should be avoided by confirming ground properties and optimising the design of the borehole array using more detailed modelling, this approach will provide the most cost effective solution.
Site specific ground properties can be confirmed by conducting a Thermal Response Test, a standard measurement of the ground thermal conductivity and the borehole resistivity; this would also quantify the consequences of an unsaturated zone and might also help identify potential benefits from groundwater flow past the array. Testing can be carried out during the drilling of the array and the results delivered in time for a judgement on whether an additional borehole is required when less conservative designs are initially being proposed.
On larger schemes, detailed heat transport modelling becomes cost effective to determine the distribution of the boreholes. Where there is complex geology or groundwater flow conditions, modelling can predict the long term performance of the ground energy source. This advanced approach may determine fewer boreholes are required, or identify advantages to specific array geometries or borehole depths, reducing project risks and often leading to financial savings.
Detailed modelling is essential for open loop schemes. Open loop systems often provide the most efficient option for larger Ground Source Energy schemes where there are suitable hydrogeological conditions. Open loop designs present a different set of challenges for an effective Ground Source Energy system.
Objectives associated with the technical design of an Open loop Geothermal Energy Scheme:
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Confirmation that the required flow rate can achieved from the abstraction well and discharged back to the aquifer
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A borehole design that is appropriate for the abstraction and reinjection to minimise the risks of borehole clogging and loss of performance
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The wells to be spaced sufficiently far apart to reduce the risk of thermal breakthrough
Regulatory approval will be required from the Environment Agency to investigate:
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The aquifer
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The abstraction of groundwater
- The discharge of groundwater back to the aquifer
Whilst the Environment Agency is supportive of renewable energy schemes, they must be satisfied that appropriate precautions are being taken to ensure no pollution or derogation of the aquifer occurs. Details of the well design and the thermal impact of the scheme must be presented to the Environmental Agency to obtain regulatory approval. ESI’s track record of working with the Environment Agency will help ensure a smooth and efficient regulatory process.
The following services are likely to be required during the design and installation of a ground source energy scheme. By completing each stage in order, any potential problems are identified at an early stage allowing an informed decision on how best to proceed can be made.
