Enfield Council have worked in collaboration with Kensa Contracting and Engie to deliver England’s largest shared ground loop array heat pump programme replacing electric heating, all in under one year and whilst the flats remained inhabited. The project serves 400 flats in eight tower blocks in Enfield was named District Heating Project of The Year at the 25th annual H&V News Awards in 2019.
The estates consist of eight 13 storey high-rise blocks each of around 50 flats. Of the circa 400 units, 318 were rented and 84 leaseholder properties. Failing to act was not an option as the heating had already failed in several properties. Renewing with new electric storage heating was considered, however, the electricity capacity available could not cover the additional electrical loadings.
While traditional schemes – such as boiler replacements, cavity and roof insulation and behaviour change advice – have been important in helping address the poverty imbalance, Enfield Council has sharpened its focus to include renewable heating which has a positive impact on both the environment and wellbeing of residents.
The total contract value was £7.3 million, with work commencing in November 2017 and completing in October 2018. The first step of the project was tenant liaison. One of the most important aspects of this scheme is that residents were able to remain in occupation throughout the works. Resident Liaison Officers consulted each household before, during, and after works. Prior to works, communal meetings were held for each block, and individual plans agreed. Residents also had access to a respite area. Opportunities were provided to view mock-up of a typical flat installation, as well as ask technical/general questions. The second step involved detailed property surveys, and borehole and riser design. The following steps were borehole drilling, trenching and headering, riser installation, and finally flat installation.
Due to space limitations Kensa removed the need for an energy centre, a traditional feature in district heating systems. This was achieved by installing a small ‘Shoebox’ ground source heat pump in each of the 400 flats, rather than a few large heat pumps centrally. The Shoebox heat pumps were connected to ambient temperature shared ground loop arrays totalling 100 boreholes drilled to depths over 200m.
One of the big advantages of a shared ground loop system is that it is relatively simple to sub-divide district schemes into smaller units. In Enfield’s case, the system was split into 16 “micro-districts” each supplying half a tower block, simplifying project logistics and allowing for parallel work flows, reduced timescales and minimising disruption to tenants.
With each flat having its own heat pump, each property is responsible for its own energy bill, and able to switch supplier; something that is not usually possible with more traditional district heating systems. 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, and the project will save 773 tCO₂ per year – a figure which will increase as the electrical grid decarbonises. As ground source heat pumps are non-combustion devices, there are zero point of use NOx, SOx or particulate emissions; a critical advantage in light of London’s air quality improvement campaign.
The project secured £4.3 million in Renewable Heat Incentive funding.
How is the approach being sustained?
Enfield is looking to follow a similar approach on other sites with the same kind of challenges.
The programme of work was an opportunity to test the large scale deployment of heat pumps, with associated lessons about the approach and cost of this type of intervention.
It has been identified that there are practical issues with heat pumps in use, including a need for residents to be provided with information about using them. This is a further area of work which is being pursued.