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These giant floating islands could keep cities warm, without burning fossil fuels

Hot Heart, a concept to store heat offshore in Helsinki, is a winner in the 2021 Innovation by Design Awards.

These giant floating islands could keep cities warm, without burning fossil fuels

Keeping the nearly arctic city of Helsinki, Finland, heated through its long winters and still kinda cold summers takes a lot of energy, whether from burning wood or consuming fossil fuels. Currently, more than half the city’s heating is provided by burning one of the nastiest of sources: coal. So when the city set a goal of becoming carbon neutral by 2035, officials there knew they needed a new alternative to keep residents warm while kicking coal out of their energy portfolio.

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They decided to ask designers for radical solutions. In 2020, the city launched the Helsinki Energy Challenge, a design competition with a $1.1 million award for the best ideas to move the city past coal to a more sustainable heat source.

[Image: Carlo Ratti Associati]

Radical solutions rolled in, and one of the most radical also ended up being one of the four winners. Hot Heart is a water-based heat storage solution set in the ocean and designed by Carlo Ratti Associati, the international architecture and design firm founded by the director of MIT’s Senseable City Lab. It is a series of deep cylindrical tanks that would store heat in the Baltic Sea, where the cylinders take advantage of water’s natural ability to store thermal energy. Combined with the city’s renewable energy capacity, heat would be pumped into the water in the cylinders when electricity is cheap to produce, and then pumped out to the coastal city’s district heating system when it’s needed—like a large, underwater battery. The concept, which is now in development with the city, is Fast Company‘s 2021 Innovation by Design Award winner for Sustainability.

“Large-sized engineering projects like this are much needed right now to help cities around the world attain carbon neutrality,” says Ratti. “Hot water reservoirs can be applied to many other cities with a similar climatic and geographical background.”

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[Image: Carlo Ratti Associati]

Thermal storage and sea-water heat pumps are relatively new but not unproven technologies. Helsinki recently opened an underground hot water reservoir to increase its thermal storage capacity, but placing the heat storage cylinders in the ocean is a novel idea—and one that opens up new potentials for the way this critical infrastructure is designed.

Carlo Ratti Associati’s concept for the floating cylinders includes enclosed roofs that would be publicly accessible. Using the heat within, they’d form dome-like warm rooms, capable of growing tropical plants and heating swimming pools.

“The design is closely tied to Finnish culture, in particular, the concept of Jokamiehen Oikeudet. It is sometimes translated as ‘the right of public access to the wilderness,'” says Ratti. “To the local people, the freedom to roam in nature is one of their core values, and we were trying to envision how to acknowledge this in the winter months, when the freezing weather renders it almost impossible to be around natural settings.”

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The public access is also about exposing people to the new tools and technologies that will be part of achieving the city’s carbon neutrality goals.

“Unlike the wars of the 20th century, the climate crisis of the 21st century has failed to inspire societal urgency. As we seek to leave behind a society of casual overconsumption in the West, we must engage people,” Ratti says. “Bringing them right to the heart of the infrastructure could help, as they would be exposed firsthand to the energy flows needed to heat the city.”

Beyond what the system can do, just building such a structure in the sea is its own design challenge. Ratti says the cylindrical basins would sit as deep as 80 feet below the surface, and the team is exploring two different solutions to stabilize them. One would involve excavating the seabed and using the rocks to form insulating walls that hold the basins. The second would anchor the basins to the seabed to prevent motion triggered by wind, sea, and ice currents.

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Placing this kind of infrastructure in the ocean saves space on land, but for ocean habitats it may be butting up against, Ratti says the concept will do no harm. “Around Helsinki, there are already a number of artificial islands, which have gone through very rigorous environmental assessment,” he says. “Our project is no different, and we have been working with marine biologists in order to make sure that it does not have any detrimental effects on the broader ecosystem.”

The exact design is still being worked out. Since the competition’s winners were announced in February, Ratti and his team have been meeting with officials from the city of Helsinki and the local utility company, known charmingly as Helen. A kickoff meeting for the next phases will happen later this fall. “They are determined to leverage the results of the competition to decarbonize the city’s district heating system,” Ratti says.

See more from Fast Company’s 2021 Innovation by Design Awards. Our new book, Fast Company Innovation by Design: Creative Ideas That Transform the Way We Live and Work (Abrams, 2021), is on sale now.

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