A successful Ground Source Energy (GSE) system provides a renewable energy solution to a building’s heating and cooling needs. These benefits depend on a reliable and efficient design of the ground loop energy source. For the system to be successful it is important that the ground loop design and size matches the profile of energy use for the building. ESI can provide the specialist skills and knowledge to ensure that the proposed ground loop size matches these needs, taking into account the balance between winter heating and summer cooling.
At sites with adequate groundwater flow beneath them, or a sufficiently large stream or lake, open loop ground source energy systems can offer significant efficiency gains over closed loop systems.
ESI Simple Open Loop Ground Source Energy Visualisation from ESI on Vimeo.
The main objectives associated with the technical design of open loop schemes are:
- Confirmation that the required flow rate can achieved from the abstraction well and discharged back to the aquifer
- A borehole design that is appropriate for the abstraction and reinjection to minimise the risks of borehole clogging and loss of performance
- For the wells to be spaced sufficiently far apart to reduce the risk of thermal breakthrough
A hydrogeological conceptual model is a key foundation to good open loop ground source energy design. ESI has many years of experience working in all the UK aquifer settings and is ideally placed to develop appropriately detailed site models. Detailed modelling of the long-term performance of the system will then inform and support ESI’s system design, ensuring the objectives are met through the appropriate location and specification of boreholes and their flow rates.
Regulatory approval will also be required from the Environment Agency to investigate the aquifer, abstract groundwater, and discharge groundwater back to the aquifer. Whilst the Environment Agency is supportive of renewable energy schemes, they will need to 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.
Borehole Design
A key issue for the development of an open loop ground source energy system is the design and completion of the abstraction and injection boreholes. The two main objectives for the borehole design are to be capable of obtaining and subsequently discharging the specified yield for the ground source energy scheme. It is important to ensure that the borehole continues to operate efficiently with no clogging or fouling. This would lead to reduced efficiency and increasing well losses during the operational life of the boreholes and an increase in the maintenance costs of the boreholes. These are familiar issues and ESI has an excellent track record in the development and licensing of water resource wells. This experience, acquired over many years and across all UK aquifer settings, can now be applied to ensuring appropriate specification and installation of the dipole wells used in open loop ground source energy installations.
ESI’s experienced hydrogeologists will specify borehole dimensions and completion standards appropriate to the aquifer setting and background groundwater quality. The boreholes will be designed to achieve the specified yield and extensive experience in working in all UK settings supports early identification where there are increased risks of borehole fouling or poor yields.
Borehole Testing
Once the design is agreed, ESI can supervise drilling and completion of the borehole and then undertake a step test or constant rate yield test. Step tests are used to directly confirm the yield that can be obtained and the borehole efficiency by interpreting aquifer properties and well losses from a single well (ESI author the Aquifer Win32 software adopted by the Environment Agency nationally for pumping test interpretation). Alternatively, following a water features survey, a constant rate pumping test may be needed to confirm that derogation to other licence holders does not occur. These tests also provide confirmation of the long term sustainability of the ground source energy scheme. ESI’s borehole design and pumping test services are generally undertaken alongside support for regulatory approval of the open loop ground source energy scheme, including a water features survey and licence applications.