News
16 Jan 2025, 13:09
Sören Amelang
|
Germany

Northern German city orders one of world’s largest seawater heat pumps

NDR

The northern German city of Flensburg has commissioned one of the world’s largest seawater heat pumps to supply climate-neutral heat through its district heating system, reports regional public broadcaster NDR. The city’s municipal utility signed a contract valued at 70 million euros with US-Irish company Johnson Controls for the heat pump. The pump, with a capacity of 60 megawatts, will keep around a fifth of the city’s 100,000 inhabitants warm.

As Germany's northernmost city, Flensburg is located at the tip of the Flensburg Fjord on the Baltic Sea, only a few kilometres from the Danish border. Installing the heat pump is part of the utility’s ambition to become climate-neutral by 2035, ten years ahead of the national target year. To achieve this aim, the utility plans to add one or two more large-scale heat pumps at a later stage. Heat pumps are much more energy efficient than conventional heating systems because they don’t generate heat energy – instead, they simply transfer it from the environment into homes.

Scheduled to commence operations in 2027, the seawater heat pump will extract thermal energy from the Flensburg Fjord. The system is designed to take in around 3,000 litres of seawater per second, slightly cooling it before returning it to the fjord. It can function under most weather conditions during the winter and use the extracted energy to heat the fluid in the district heating pipes, which run through the entire city, to between 60 and 95°C. Operating the necessary compressors will require approximately 20 megawatts of electricity, which the utility plans to source exclusively from renewable energy providers.

Operation of the heat pump could become problematic during extreme cold snaps, precisely when the need for heating is at its highest, according to the article. The large heat pump can only run at full power when water temperatures are higher than 8 degrees Celsius, as it cools the water down and ice formation would damage the system. Provisional measurements suggest operation might not be possible for around two weeks every year.

The commissioning of the heat pump in Flensburg is part of a broader trend towards large water-based heat pumps as cities clean up their heating systems. The capital on Flensburg's home state Schleswig-Holstein, the city of Kiel, also plans to install seawater heat pumps, intended to start operations in 2028. The Danish town of Esbjerg recently started operating the world’s largest seawater heat pump, which takes in 4,000 litres of North Sea water per second to heat 25,000 households. A growing number of towns in southern Germany are also exploring whether they can tap into the water of Lake Constance, Germany's largest lake, for their switch to climate-neutral heating.

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