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Data Centre Heat Reuse: Why Distance to the Buyer Decides

Two Danish data centre projects made the news in October 2026. Both promise to reuse their surplus heat. Neither is built yet, and both still depend on decisions made outside the data centre fence. But they give very different answers to the same basic question: where is the buyer of the heat?

In Kalundborg, the heat is meant to travel towards Copenhagen, through a pipeline that has not yet been decided. Near Ølgod, the buyer is planned on the same site. This article looks at both projects and at the engineering underneath the promise.

Kalundborg: 850 MW and a pipeline still on the drawing board

A data centre with 850 MW of grid capacity is being planned in Kalundborg, on around 150 hectares south of the town’s industrial park. The project still needs permits and the municipality’s final decision. The developer says the surplus heat will go to district heating, and estimates that it could cover 25 to 30% of the district heat Copenhagen will be short of in 2050. The argument rests on a planned district heating line from Kalundborg to the capital.

That line already has a history. Since 2025, a consortium of VEKS, Novo Nordisk, Holbæk and Kalundborg municipalities, Kalundborg Forsyning and Ørsted has studied a transmission line that would carry industrial surplus heat from Kalundborg towards the Copenhagen area. Ingeniøren described it as more than 100 km of buried pipe. The partners have chosen a route that connects to the capital’s network at Roskilde and delivers heat along the way in Kalundborg and Holbæk. They are still working out whether a municipal project company should build it.

The idea is not new. Ingeniøren reported in March 2025 that the project had been on the drawing board for several years, stalled in 2024 when it proved too expensive and risky, and was then revived by Novo Nordisk.

VEKS has been open about the economics. The project is cost heavy, requires depreciation over up to 50 years, and carries more risk than the utility’s other surplus heat projects. Ownership of the line, during both construction and operation, is still to be settled.

There is one more detail. The line was conceived for industrial heat, and Kalundborg already has more surplus heat than it can use locally. A VEKS memo assumes that the industrial symbiosis in Kalundborg can produce more than 220 MW of surplus heat, of which VEKS estimates it can take around 120 MW. Heat from a new data centre would have to find room in a pipeline planned for someone else’s heat. The data centre’s heat promise rests on infrastructure that was developed for industry, and that has not yet been decided.

Ølgod: the buyer on the same site

On 6 October 2026, Varde Municipal Council approved the local plan for a combined data centre and greenhouse project at Krageris, north of Ølgod. The 174 hectare site allows up to 225,000 m² of data centre and up to 475,000 m² of greenhouses. The surplus heat is to warm the greenhouses so that vegetables can be grown all year. atNorth leads the project, Selected Group will build and run the greenhouses, and completion is expected in 2030.

Here the heat does not need a long transmission line. The source and the buyer are planned together, in the same local plan, from the start.

A third model: the network next door

Denmark already has a working example that sits between the two. Microsoft’s data centre in Høje-Taastrup supplies surplus heat to VEKS. It works because the data centre lies close to existing heat infrastructure and a residential area. VEKS installs heat pumps that raise the temperature before the heat is sent into the district heating network.

The physics: heat loses value with distance

Moving heat costs in three ways. The pipe has to be dug in. Pumps use electricity to move the water. And the water loses heat on the way. All three grow with distance. A line of more than 100 km is not a connection, it is a long-term infrastructure asset that has to be financed and maintained for decades.

Friction is a large part of that bill. Long heat lines have always been a fight against it, with engineers looking at everything from larger pipe diameters to additives that help the water flow more easily. Materials and pumps have improved, but the principle has not changed: every kilometre is paid for in pumping energy, year after year.

Temperature changes the calculation. A data centre delivers low-grade heat. In the designs we work with, return water reaches up to 56 °C when servers run with 60 °C exhaust air, and around 38 °C at 45 °C exhaust air. How warm the water gets depends on how warm the operator is prepared to run the servers.

The warmer the water, the lower the flow needed to move the same amount of heat. Lower flow means smaller pipes, smaller pumps and less equipment, both inside the data centre and on the way to the buyer. Warmer water also leaves less work for any heat pump that has to lift the temperature to network level.

Season matters too. Residential district heating demand falls in summer, while a data centre produces heat all year. A greenhouse built to produce year round gives the heat a use outside the residential heating season.

What to ask before counting the heat

Long transmission lines can make sense. A capital region is a large and stable buyer, and Kalundborg’s industrial heat is real. But distance is a bill, and someone pays it for many years.

For a municipality or a utility, the first question is therefore not how much heat a data centre promises. It is who takes the heat, how close they are, at what temperature, and in which months. The next questions follow from the answers: who builds and owns the pipe, and who carries the cost over its lifetime.

Surplus heat is only valuable when temperature, flow, distance and system design fit together. The projects that answer those questions early are the ones most likely to deliver on the promise.

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