CRA-Carlo Ratti Associati - Hot Heart, The “floating forests” for a sustainable and ecological future
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Hot Heart, The “floating forests” for a sustainable and ecological future

CRA-Carlo Ratti Associati

Urban Planning  /  Future
CRA-Carlo Ratti Associati
Hot Heart is a winning proposal for the Helsinki Energy Challenge by the Municipality of Helsinki,
with the goal to decarbonize its district heating system by 2030. The project, unprecedented in
scale for endeavors of its kind, is based on 10 cylindrical heat-storing basins floating on the sea
off the city’s coast. Each measuring at 225 meters in diameter, these basins have a combined
capacity of 10 million cubic meters.

Hot Heart functions like a giant thermal battery. Production of renewable energy is getting
cheaper, but storage is still extremely expensive. Under this system, low- or negative-cost
renewable electric energy (harvested elsewhere) is converted into heat, stored in the system and withdrawn into the city’s heat distribution channels during the winter when demands are high. Our financial estimates suggest that by the end of the decade the system would not only pay back its cost but fully cover the heating needs of Helsinki at a cost 10% cheaper than today.

In addition, the “archipelago” also serves as a hub for recreational activities. Four of the 10 hot
water reservoirs are enclosed in transparent domes to create “floating forests,” under which
tropical ecosystems from around the world are cultivated, naturally heated by the basins
underneath. Each “floating forest” would simulate four of the worlds – the Amazon, Congo,
Borneo, Central America.

The “floating forests” was inspired by two key concepts. Firstly, it addresses our inner biophilia,
an innate yearning to be around natural elements, as proposed by Harvard biology professor E.O. Wilson. By joining natural and artificial elements together, the project improves the urban
environment as establishes nature as an important pillar of our lives. Citizens can socialize with
one another or enjoy the greenery at peace, while international travelers can also explore
different ecosystems in one place.

The second concept is specifically tied to the Finnish culture. The local people have long
embraced the idea of Jokamiehen Oikeudet, which is sometimes translated as “the right of public access to the wilderness.” While this freedom to roam is deeply rooted in the Finnish society, the citizens’ connection to the countryside is mostly limited during the months of freezing weather. Hot Heart’s sustainably-cultivated tropical environments were conceived to remedy this situation. It provides visitors with additional public place to socialize and enjoy the sunlight – the LED Sun-Like technology allows people to stay warm inside, even in the harsh Nordic winter.

Hot Heart has immense potential in carbon reduction. Designed to be replicated in other coastal cities around the world with a similar climate, it could become an important piece of green infrastructure in the urban societies of tomorrow.


 City of Helsinki
 397600 mq
 CRA-Carlo Ratti Associati
 Carlo Ratti, James Schrader, Alberto Benetti, Federica Busani, Rui Guan, Stephanie Lee, Juan Carlos Romero, Chenyu Xu
 Ramboll, Transsolar, Danfoss Leanheat®, OP Financial Group, Schneider Electric, schlaich bergermann partner, Squint/Opera
 CRA-Carlo Ratti Associati


CRA-Carlo Ratti Associati is an international design and innovation practice based in Turin and New York. Drawing on Carlo Ratti’s research at the Massachusetts Institute of Technology, the office is involved in many projects across the globe, embracing every scale of intervention from furniture to urban planning. Among the recent designs are the Italian Pavilion at Expo 2020, CapitaSpring tower in Singapore, MEET Digital Arts Center in Milan, and the Eyes of the City exhibition at the 2019 Bi-City Biennale of Architecture and Urbanism of Shenzhen. In March 2020, CRA initiated CURA, a global open-source initiative to convert shipping containers into ICU pods for COVID-19 patients. It is also the only design firm whose works have been featured three times in TIME Magazine’s ''Best Inventions of the Year'' list. In the last years, the office has been involved in the launch of Makr Shakr, a startup producing the world’s first robotic bar system, and Scribit, the write&erase robot.

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