Heat networks Upgrading the network
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Southwark project overview
Consort – 1 x Hi1000: 1,000 kW WSHP Newington – 2 x Hi600: 600 kW WSHPs Wyndham – 2 x Hi600: 600 kW WSHPs
The project took just under two years in total, from July 2020 to September 2022
network design and build company, ICAX, demonstrates how to overcome some of the challenges of retrofit in residential properties, including how to manage disruption while people are still living in their homes.
Inner-city heat network
Graham McDermott, from J&E Hall, explains how a recent project at Southwark used innovation and planning to ensure residents weren’t disrupted by a much-needed heat network heat pump overhaul
H
eat networks are being put forward as an important way to reduce the carbon footprints of our towns and cities, providing
a practical solution for multiple buildings. While the government plans to future-proof new buildings to ensure their readiness for district heating, there is still much to be done in the retrofit sector, upgrading existing schemes with the latest low carbon technologies At the time of writing, the government has launched a heat network zoning consultation setting out the types of buildings that would be required to connect to a district heating system in designated areas, with proposals designed to establish and enforce this way of heating. At the moment, the government estimates that around 2% of heat demand is currently provided through heat networks, by 2050 it expects that close to a fifth of national demand for low carbon heat could be met by district heating solutions, including retrofits. The government’s proposal focuses on new buildings, with the suggestion that any new properties are made ‘heat network ready’ through
In the London Borough, over 2,000 homes have had their existing gas-fired district heating systems upgraded with water source heat pumps (WSHPs), which J&E Hall developed exclusively for the project. Five WSHPs have been installed at three sites, at Consort, Newington and Wyndham, replacing existing gas-fired boilers as part of Southwark’s climate strategy and action plan - council buildings are responsible for 75% the borough’s carbon emissions with the highest emissions coming from residential properties, at 28%. Mostly funded with a low interest loan of
£7 million from the Mayor of London’s Energy Efficiency Fund, which will be repaid with income from the government’s non-domestic Renewable Heat Incentive (RHI), it is predicted that the WSHPs will save 1,744 tonnes of CO2e per annum. Energy usage will be cut by over 34% and local air quality will also be improved by stopping the pollution caused by gas combustion. Water for the heat pumps is taken from the London Aquifer, so the scheme is non-consumptive. It also benefits the Aquifer by dropping the temperature of the returning water, counteracting overheating caused by the buildings that use this water for ‘free cooling’.
the specification of correctly sized radiators and metering systems. While this is welcome news, there is a lot to be done with existing district heating systems, many of which still rely on gas boilers. Our recent project in Southwark with heat
Bespoke WSHPs from J&E Hall
The WSHPs at Southwark are bespoke, using new refrigerant, R515B, a mixture of HFO-1234ze(E)/HFC-227ea. R515B has a low GWP (299) and a relatively low condensing pressure at high temperatures. Using this refrigerant allowed the heat pump to be built with a single stage HallScrew compressor, which simplified the design and reduced capital costs. A single compressor is unusual in high temperature heat pumps; ordinarily to achieve hot water of 75°C and above two compressors are required in series. To further improve efficiency, a shell and tube water cooler with an integral sub-cooler and a water-cooled
condenser heats the water supplied to the heat network. All the heat exchangers have been designed with very small approach temperatures (the temperature difference between the refrigerant and the water).
Working around residents
One of the biggest challenges of a residential heat pump retrofit, is residents. It’s not practical to ask people to leave their homes. At Southwark, the mains gas-fired boilers remained live during the installation process and have been retained to provide back-up on the very coldest days. A 3D model was built for each plantroom for ease of co- ordination with existing services. We also designed the WSHPs to work with
the existing pipes and radiators, with a high temperature flow and return of 75/70°C so the heat pumps deliver the same hot water output as a gas boiler. The buildings serviced by the heat network will be upgraded with energy efficiency measures over time, as this happens the flow temperatures can be lowered accordingly. Even at high temperatures, however, the system is still very efficient achieving a coefficient of performance of 2.9.
32 February 2024
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