A combination of favourable ground conditions and borehole configuration at the site of a current ground-source heat pump retrofit project at Daisyfield, a development of 183 flats across three high-rise tower blocks in Blackburn, UK, owned by Together Housing Group, has offered the opportunity for Kensa to trial increasing drilling depths to 300m, as part of its ongoing investigations.

"Ground-source heat pumps are highly efficient, non-combustion devices, and therefore the low-carbon renewable heating option of choice," explains Dan Roberts, operations director at Kensa Contracting, who was involved in the work. "Despite this, the technology is vastly underused within the UK. Often with large-scale developments, this is due to sites having insufficient space to install the number of boreholes needed to meet the heat demand of the properties.

"By increasing the standard depth of 100-200m and drilling between 300-400m where geological conditions allow, more pipe could be installed in the ground for the same amount of surface area. As well as allowing extra energy absorption, by installing the loops deeper the drill rig isn't required to move as often, which reduces the time spent on the drilling phases, therefore lowering installation costs."

Depending on the viability of the ongoing trials, over the next year, Kensa Contracting plans to work with the supply chain to develop complimentary grouting and installation methods that allow regular, safe, and effective drilling of medium-depth boreholes.

The installation of low-carbon, ground-source heat pumps at Daisyfield is part of an ongoing partnership between Together Housing Group, one of the largest landlords in Northern England, and Kensa Contracting.

Since 2018, Kensa has retrofitted ground-source heat pumps as part of a three-year programme to tackle fuel poverty and reduce the carbon footprint of over 700 homes in the social landlord's property portfolio. Residents across multiple sites in Yorkshire and Lancashire with the efficient new systems already installed are reaping the benefits of increased levels of comfort and lower heating costs.

On the back of those results, Together decided to expand Kensa's schedule of works, which was already the largest of its kind in the UK to date, by adding the towerblocks at the Daisyfield site in Blackburn, Lancashire.

The 183 flats are currently heated by old and obsolete gas boilers, which Together is keen to decommission and replace with more efficient and environmentally friendly Kensa heat pumps to move away from a reliance on fossil fuel.

Due for completion in early 2021, the project is estimated to produce lifetime carbon savings of 6,556t of CO₂ (based on SAP10 carbon factors). This is the equivalent of removing 1,416 cars from the road for a whole year.

The new ground-source heat pump systems at Daisyfield are part of a £4.6million (US$5.9 million) scheme of improvements that Together has committed to completing in the tower blocks, including electrical upgrades and new safety measures, such as fire doors, fire alarms, and sprinkler systems to safeguard residents. So far, feedback from residents has been very positive, indicating that they are happy that gas is being removed from their homes.

Patrick Berry, MD of Together Energy Services, says: " This is a challenging and complex project combining the replacement of the heating system alongside the installation of a sprinkler system, new alarm system and upgrade of the buildings' electrical infrastructure. All of this is being completed with the tenants in their homes. We are therefore delighted to be working with Kensa Contracting to both manage and deliver this project for the benefit of our tenants and the decarbonisation of our stock."

Shoebox heat pumps on shared ground loop arrays

Inside each of the flats, individual Kensa Shoebox ground-source heat pumps will be installed linked to a radiator system, which will be upgraded where necessary.

The Shoebox model is compact, quiet, and highly efficient; perfect for flats where space is at a premium, as it can be fitted inside airing cupboards or kitchen cabinets. Generating heat at the point of use, the system produces hot water temperatures up to 65C for domestic hot water and is as quiet as an average fridge freezer.

The Shoebox heat pumps will be linked to an array of shared ground loop boreholes drilled underneath the green spaces and car parks adjacent to the tower blocks. The system collects the energy from the underlying rock and distributes it at ambient temperature to the heat pumps, which then upgrade it for use in the flats. The system is also heating communal areas within the tower blocks and a ground-floor café.

This system design is very efficient, as high-grade heat is only generated at the point of use by the ground-source heat pump, and only when required. This is an alternative system architecture to traditional district heating, where heat is generated in a central plant and then continually circulated through the system, which leads to significant heat losses and potential overheating in risers and communal areas. The use of distributed heat pumps also removes the need for a plant room, complex metering and billing arrangements, and restrictive energy supplier contracts.

Testing the potential for medium-depth boreholes at Daisyfield

Kensa partner GeniusEnergyLab carried out extensive investigation across the Daisyfield site to determine ground conditions and thermal conductivity prior to the borehole drilling. The site geology was found to be made up of clay with gravels down to 11m below ground level, followed by mudstone, siltstone, and sandstone to 300m below ground level, whereupon coal bands were discovered and drilling could not continue below these depths due to coal authority permissions.

 

GeniusEnergyLab then used specialist thermal modelling software to calculate the performance of the ground array to ensure the most efficient and cost-effective solution.

Chris Davidson, CEO and technical director of GeniusEnergyLab, comments: "It's very exciting to be involved in this trial which will open up even the most congested of city centre locations in the UK to ground-source heat pumps and all the carbon reduction and cost-saving benefits they convey.

"This practical demonstration builds on years of modelling and installation experience from a fantastic team of companies collaborating at the cutting edge of the technology."

The borehole drilling is being carried out by expert drillers, Geodrill Ltd, with whom Kensa has partnered on many projects. In total, 84 boreholes will be drilled across the Daisyfield site, totalling 16,146m of boreholes.

Paul Turnbull, MD at Geodrill Ltd, says: "We are privileged to be involved with the Daisyfield project where we drilled to 300m. Medium-depth borehole drilling is on the increase; we find ourselves being asked to drill to depths of 300m plus more frequently when the norm used to be between 100-150m deep.

"It is the continued investment in equipment that makes this deeper drilling possible; with the addition of more powerful rigs and mud pumps, as well as more efficient mud cleaning systems, we are able to exploit the potential of medium-depth boreholes, creating more opportunities for ground source."