Aims of the project:

Kensa Contracting and ENGIE delivered England’s largest shared ground loop array heat pump project to replace electric heating in 8 tower blocks for Enfield Council.

The tower blocks were previously heated by direct electric underfloor heating that was electrically powered directly from Enfield Council’s landlord supply. This is an expensive and high carbon source of heat. The tenants had no control over the heating which often lead to them opening windows to control the temperature. There was also no metering provision and therefore tenants paid a fixed monthly fee to cover heating regardless of how much heat they required. Typical annual heat costs were £800 – £1,100 per flat – putting many tenants into fuel poverty and causing Enfield Council to have serious concerns about the health and wellbeing of their tenants.

Kensa Contracting and ENGIE drilled a total of 100 boreholes with depths ranging from 197 – 227m across the 2 sites. These were connected to the tower blocks via underground header pipes and riser pipework running through the stairwells providing a source of heat to 402 flats.

A compact and ultra-quiet Shoebox ground source heat pump from Kensa Contracting’s sister company, Kensa Heat Pumps, was installed within each flat along with a hot water cylinder. Every flat has their own heating and hot water controls, and as the heat pumps were all connected to the flat’s own electrical supplies, every tenant automatically only pays for the heat they actually use – simply via their electrical bills. Because of the high efficiency of the heat pumps (300%), the heating and hot water costs for each tenant are now £350-400 per year representing a massive saving and making a significant difference to tenant’s finances.

Key challenges:

Central plant rooms for this type of urban environment present a massive challenge as space is so tight across both sites.

Kensa solved this issue by entirely designing out the need for an energy centre. This is achieved by installing small heat pumps in every property rather than 1 or 2 large heat pumps centrally. The need for central pumps was also designed out by supplying the ground circulation pumps within each heat pump. Kensa’s shared ground loop approach mimics the gas network, the array is entirely “passive” with no working parts which also means there is no need for a landlord’s electrical supply and no requirement to apportion the costs of running any central plant across the flats.

This shared ground loop approach is also exempt from the Heat Network (Metering and Billing) Regulations 2014 as each tenant automatically only pays for the heat they use through their electric bills.

In total, there are 402 distribution points taken to the entry point of each flat. One of the big advantages of a shared ground loop system is that, unlike central plant systems, it is relatively simple to sub-divide district schemes into smaller units. In this case, Kensa decided to split the system into 16 “micro-districts” each supplying half a tower block.

This greatly simplified the logistics of the project allowing for parallel work flows and reduced the overall timescales and disruption to tenants. The internal installations commenced just 8 weeks after the start of the borehole drilling – in a central plant scenario, it would have been at least 20 weeks before the heat interface units could be started – adding 3 months to the overall schedule and delaying when tenants could be taken off the high cost electric heating.

In total, including the boreholes, headers and risers, the system comprises 48,000m of 40mm MDPE pipe in the boreholes and headers, 4,800m of 110mm underground header pipe, 1,120m of 110m insulated riser pipe (in the stairwells) and 4,160m of 28mm insulated distribution pipework to each flat. The majority of the pipework is underground and at ambient temperatures which means there is no heat loss and no need for insulation. This vastly reduces the cost of the pipe and the labour required to install it. All above ground pipe is insulated but that is only for condensation protection – there are still no heat losses in these sections. In addition to making the system more efficient, it also avoids the communal area overheating issues commonly found in district heating systems.

Key success factors:

Tenants have saved £450 – 700 per year in heating and hot water costs, giving nearly £9 million in collective lifetime bill savings over the nominal 40 year system lifetime. For many this means no longer having to live in fuel poverty, allowing them to heat their flats properly, thus improving their health and wellbeing.

The EPC ratings on the properties have improved by an average of 8 points helping Enfield towards its target of stock improvement.

The project will save 773tCO₂ per year – a figure which will increase as the electrical grid decarbonises.

Ground source heat pumps are non-combustion devices, there are zero point of use NOx, SOx or particulate emissions.

As shared ground loop arrays are classed as district heating, the project was eligible for funding from the Non Domestic RHI, delivering £4.3million to Enfield Council over 20 years. Coupled with upfront investment from the ECO grant, Enfield Council are set recoup their capital costs for delivering the project. This represents excellent value for money that no other heating technology can compete with and allows Enfield Council to sustainably re-invest into further energy saving projects.

Key learnings:

This project was successfully delivered by Kensa in under a year, all whilst keeping all the flats occupied and represents one of the most significant and ground-breaking milestones for district heating, ground source technology and the renewable energy industry as a whole.

Kensa’s district heating system architecture comprising a shared ground loop with individual heat pumps produces the multiple benefits of reduced fuel bills, energy security, electrification of heat, decarbonisation and reduction of particulate emissions. This project demonstrates that the system can be deployed rapidly and at large scale and represents a blueprint for the future of heating in tower blocks across London and the rest of the country.

The system is flexible enough to accommodate tower blocks, low rise flats, streets of houses and commercial buildings. It can also be adapted to take advantage of other available sources of heat including surface water, tube cooling, office block cooling or waste heat from energy from waste plants.

Project details:

Organisation: Enfield Council, ENGIE & Kensa Contracting

Funding: Enfield Council financed the project. Costs are offset by upfront grants via the ECO and 20 year quarterly income via the RHI.

  • Cost of the scheme just under £5 million – around £12,400 per flat;
  • Estimated RHI income over 20 years is £4.3 million (£10,700 per flat);
  • ECO funding of up to £500,000 (£1,250 per flat);
  • Combined RHI and ECO over 20 years offsets the initial capital investment, offering excellent value for money which no other heating technology can compete;
  • This was one of the main reasons why Enfield Council chose Kensa’s shared ground loop ground source heat pump (GSHP) solution – it was financially more attractive (for both Enfield and the end users’ running costs) than the alternatives, which included central plant air source heat pumps or electric storage heaters;
  • The offset capital expenditure allows the council to sustainably reinvest into further energy saving projects.

Total project cost: Just under £5 million.

How long the project took from concept approval to implementation:

  • October 2016 – Tender call released
  • September 2017 – Contract signed
  • November 2017 – Start on site
  • August 2018 – Complete

How long has the project been operational: Since August 2018.

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