Aarhus utility company Kredsløb inaugurated six large seawater heat pumps on Aarhus Ø on September 10, drawing district heating out of the water in Aarhus Bay.
The pumps were opened on Thursday as the first stage of a larger project, DR reports. The plant sits underground on Aarhus Ø, where water is pumped in from the bay and later returned to it.
Kredsløb chief executive Bjarne Munk Jensen puts the investment at 300 million kroner, according to DR. The same figure is reported by CTwatch, which also covered the opening.
Din Avis reports that the six pumps are housed in a facility called Maskinrummet. Together they can use energy from up to 1.2 million liters of seawater per hour. That corresponds to the annual heat consumption of about 1,900 households.
A similar figure is reported by Århus Stiftstidende. According to Din Avis, Kredsløb plans 14 seawater heat pumps in total. Eight more are to be built by 2028 at the old Aarhusværket site in Sydhavnen, bringing supply to around 5,000 households.
Replacing wood pellets
Aarhus City Council has decided to phase out about 600,000 tons of wood pellets burned each year to heat the city, DR reports. The pellets have been fired at Studstrupværket outside Aarhus.
The heat pumps are to work alongside a large geothermal plant in Skejby. That plant draws warm water up from the underground, according to DR.
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Kredsløb states that the seawater heat pumps deliver three and a half times more energy than the electricity used to run them. Munk Jensen says the technology can also supply radiators during a cold winter. Water is taken from the bottom of the basins, where it does not freeze.
Brian Vad Mathiesen, professor of energy planning at Aalborg University, calls the pumps a sensible part of the district heating conversion in Aarhus. He notes that they work most economically when there is cheap electricity from sun and wind. For that reason, he says, Danish heat supply needs many sources of renewable energy.
According to Mathiesen, a district heating system cannot rest on seawater heat pumps alone. When power prices are low, the pumps can run, and other resources can be used when prices rise. He describes that combination as the basis for supply security and more stable economics for customers.
Aarhus follows Esbjerg, which opened a large plant in 2024, and Aalborg, where a facility is planned to cover a third of the city’s district heating needs, DR reports. Munk Jensen says Aarhus cannot rely as heavily on the technology because of a lack of space. The city has no large unused harbor areas, and its coastline is covered by forest or buildings.
