Aarhus turns seawater into heat for 5,000 homes

Aarhus is commissioning six seawater heat pumps that will extract heat from Aarhus Bay and help warm thousands of homes, DR reports.

The pumps, operated by utility company Kredsløb, are located at Aarhus Ø. Water is pumped in from the bay, passed through the facility and returned to the water.

Kredsløb is building 14 seawater heat pumps in total at Sydhavnen and Aarhus Ø. Together, they are expected to supply enough heat for about 5,000 households.

The project will work alongside a large geothermal facility in Skejby, which draws hot water from underground. The two sources are intended to help replace the wood pellets burned at Studstrupværket outside Aarhus.

The investment is 300 million kroner. According to Kredsløb chief executive Bjarne Munk Jensen, the pumps produce three and a half times more energy than the electricity needed to operate them.

The technology can also provide heat during a cold winter. The water is taken from the bottom of the basins, where it does not freeze, Jensen said.

At full capacity, the six pumps at Aarhus Ø will use 1.2 million litres of water per hour. The eight pumps at Aarhusværket will use another 2.6 million litres per hour. In total, 3.8 million litres of seawater will pass through the pumps each hour.

Aarhus City Council has decided to phase out about 600,000 tonnes of wood pellets burned each year to produce heat for the city, creating a need for other heat sources.

Brian Vad Mathiesen, a professor of energy planning at Aalborg University, said seawater heat pumps were a suitable part of Aarhus’s transition to a different district heating system. They are most economical and efficient when powered by cheap electricity from solar and wind energy, he said.

However, Mathiesen stressed that a district heating system cannot rely solely on seawater heat pumps. Using several sources allows the pumps to run when electricity prices are low, while other resources can be used at other times. This improves security of supply and creates a more stable economy for the district heating system and its customers, he said.

Aarhus cannot cover as large a share of its heating demand with seawater heat pumps as Esbjerg and Aalborg because it lacks space, Jensen said. The city has no large unused harbour areas, while much of its coastline is occupied by woodland or buildings.