Revolutionising District Geothermal Heating with Open Loop Borehole Technology

Igne recently supported the construction of a low-carbon housing development in London.  Over 1,900 homes and 47,000 square feet of employment, industrial and community space were constructed on a brownfield site.  The primary source of heat for the entire community’s energy centre was to come from an innovative, low-carbon, open-loop ground source heat pump (GSHP).

This open loop geothermal system will provide 1.5MW of sustainable heating with an estimated carbon saving of 24,000 tonnes over 30 years. This project has been shortlisted for the Ground Engineering Sustainability Award.

The pump is designed to extract water from aquifers below the Earth’s surface via deep boreholes to enable the harnessing of the power of geothermal heat.  Igne drilled, installed, tested and proved the boreholes.

This development is one of the first brownfield residential communities in the UK to be served by a GSHP heating network, but by partnering with Igne, your next housing development can enjoy the same sustainability benefits. 

A summary of works for the open loop district heating scheme:

Our work on the project was delivered in two phases and we drilled two abstraction and three injection boreholes in total.

The project presented several challenges, including complex ground conditions, a requirement to drill as unobtrusively as possible on an active and busy construction site, as well as ensuring seamless integration with existing infrastructure.  

Our team navigated these obstacles with precision and expertise, laying the groundwork for a pioneering heating system.

The drilling phase explained:

We employed a meticulous drilling programme, drilling the top section in a 508mm diameter to install 25m of grouted 406mm steel casing.  Drilling then continued in a 375mm diameter to the final depth of 135m below ground level.

Once the drilling phases were completed, 315 x 285mm PVC casing was installed into each borehole to depth, and headworks were completed to specification with a flange connection, biscuit, and cover.

To maximise the yield, the boreholes were developed using acidisation at the end of phase two.  Once it had reacted as anticipated, the acid was airlifted, checked, neutralised, and safely removed from site.

The boreholes were drilled with careful attention paid to maintaining structural integrity.  A combination of steel casing and PVC lining ensured durability and efficiency, setting the stage for optimal heat extraction.

The completion of drilling marked the beginning of comprehensive testing and development procedures.  Igne installed borehole pumps and overground pipework to facilitate water pumping tests, ensuring the suitability of the boreholes for heat extraction.

Rigorous step-tests and constant rate tests evaluated the system's performance under varying conditions, guaranteeing reliability and efficiency.

The test pumping phase summarised:

Igne undertook a programme of development pumping from three boreholes to ensure discharge rates of no more than 54 cubic meters per hour (m3/hr), which is circa 15 litres per second (l/s) over a period of up to 72 hours.  This test was needed to ensure the boreholes were well-developed and all suspended solids were removed.

Following the development pumping phase, a period of 48 hours rest was allowed to allow water levels to stabilise.

Then, step-tests, comprising of four steps each no less than 120 minutes in duration were commenced.  Maximum rates of pumping and overall duration of the test were not to exceed 54 m3/hr (~15l/s) and 12 hours respectively.

Three constant rate tests followed on where we abstracted from three individual boreholes at constant rates, not exceeding 54 m3/hr (~15l/s) over a period of 48 hours - or until groundwater levels monitored in observation wells had stabilised.

We also undertook an abstraction-recharge constant rate test by abstracting simultaneously from two boreholes and discharging the abstracted groundwater to all three injection wells, with the combined rate of groundwater being abstracted and recharged not exceeding 220 m3/hr (~61l/s).

The test was to be completed over 48 hours - or until groundwater levels monitored in observation wells stabilised.  Recovery tests of at least 24 hours, or until groundwater levels monitored in all observation wells stabilised, were conducted after each test.

The purpose of the intense testing phase was to ensure the long-term viability of all abstraction and reinjection boreholes.  Through this meticulous planning and execution, Igne successfully demonstrated the feasibility of open loop geothermal boreholes for district heating applications.  

This project's success paves the way for widespread adoption of geothermal technology, offering communities a cost-effective and environmentally friendly alternative to traditional heating methods.

Igne's pioneering approach to district geothermal heating represents a paradigm shift in sustainable energy solutions.  By harnessing the Earth's natural resources with precision and innovation, Igne has laid the foundation for a future where clean, efficient heating is accessible to all.  As communities seek to reduce their carbon footprint and embrace renewable energy, Igne stands ready to lead the way towards a brighter, more sustainable future.

Our open loop solutions are suitable for large developments; we also have closed loop alternatives for small and self-builders.  Contact us to discuss your heating and cooling ambitions, and how our end-to-end solutions can help you.