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Cool ways of using low grade Heat Sources from Cooling and Surplus Heat for heating of Energy Efficient Buildings with new Low Temperature District Heating (LTDH) Solutions.

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Letting no warmth go to waste

An EU-funded project has developed and demonstrated the full value chain of innovative solutions for warming entire neighbourhoods using recycled low-temperature heat.

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The current energy crisis is fuelling fresh interest in district heating as an effective means of delivering low-carbon energy. Enabling such systems to run on surplus heat at low temperatures could further reduce our reliance on fossil fuels. The EU-funded COOL DH project has delivered a broad range of methods and tools for making this possible and demonstrated their effectiveness in real-life scenarios. “We have gone all the way from planning and building business cases to production, low temperature distribution and end-user installations,” says Reto Michael Hummelshøj, leading project manager at the engineering consultancy COWI, the company coordinating the project. The COOL DH team deployed low-temperature district heating (LTDH) solutions in an existing city district of Høje-Taastrup, Denmark, and in an entirely new district in Lund, Sweden.

Renewable and recycled

In the Østerby district of Høje-Taastrup (Denmark), traditional district heating was converted to LTDH, reducing heat loss from above 35 % to about 16 % without any building refurbishment. Energy is supplied to the system by a photovoltaic installation with a heat pump at a local shopping mall providing both heating and cooling to the surrounding areas, and by waste heat from the cooling machines of a bank’s data centre. The system serves a total of 159 dwellings. In 2021, the installations enabled CO2-eq savings of 617 tonnes. In the brand-new Brunnshög district of Lund (Sweden), the main source of low-grade waste heat is a particle accelerator at the MAX IV research facility. This heat is made available to the district through a network set to become Europe’s largest LTDH facility, also drawing on other renewable energy sources. Currently serving just 200 consumers, the system has already been able to increase non-fossil fuel supply by around 25 GWh in 2021. “Once the district is fully built, it will serve about 40 000 people living and working there,” Hummelshøj notes.

Raising the bar

One of the project’s key innovations involved the development of a new type of PE-RT pipe, which uses polyethylene with raised temperature resistance. The pipes offer benefits including easier deployment (as they can literally be rolled out), a leak detection system, better insulation and operation at higher pressures of up to 13 bar in LTDH systems, enabling reduced heat loss. Several kilometres of PE-RT pipes have been deployed at both demonstration sites. The pipes could also offer the possibility of using electrofusion weldings. When this process is standardised, it could help remove a major bottleneck, Hummelshøj explains: “There is a lack of certified steel welders. Electrofusion fittings would enable normal workers to connect pipes with just a few days of training.” Other key technical developments include a solution to recover all heat loss from district heating pipes. It uses collector pipes running parallel to these pipes and a small, dedicated heat pump which runs on renewable electricity, too. The project team also addressed the issues of legionella bacteria building up in the water through a collaboration with companies commercialising antibacterial water treatment units.

Large-scale opportunities

Looking ahead, Hummelshøj is confident that the solutions developed as part of COOL DH have huge potential for deployment at a larger scale. “In the consortium, we developed the full value chain and built the knowledge to replicate it in other sites,” he adds. In Sweden and Denmark alone, there are more than 800 district heating networks where LTDH solutions could be applied. The predicted boom in Power-to-X technologies could also become a driver of LTDH, as these plants will generate large amounts of surplus heat.


COOL DH, low-temperature district heating, district heating, LTDH, surplus heat, energy crisis, low-grade waste heat, PE-RT pipe, heat pump, legionella, Power-to-X

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