The project was developed by CRA-Carlo Ratti Associati in collaboration with SpaceForm, Ramboll, Transsolar, Danfoss Leanheat®, Schneider Electric, OP Financial Group, schlaich bergermann partner and Squint/Opera.
The project is based on an archipelago of heat-storing basins with the dual function of storing thermal energy and serving as a hub for recreational activities. The “islands” will also be home to tropical forests and ecosystems from around the world, giving the Finnish capital additional public space and a new educational attraction.
Located off the coast of Helsinki, Hot Heart will be the largest infrastructural facility of its kind. The project consists of a set of 10 cylindrical basins, each measuring 225m in diameter. They collectively can hold up to 10 million cubic metres of water. The system functions like a giant thermal battery: low- or negative-cost renewable energy is converted into heat, stored in the tanks and withdrawn into the city’s heat distribution channels during the winter.
In addition to its thermal storage properties, Hot Heart doubles as an accessible recreational venue. Four of the 10 hot water reservoirs are enclosed in transparent domes containing the “Floating Forests”, tropical ecosystems from the world’s key rainforest zones naturally heated by the basins underneath. The “Floating Forests” provide visitors with a place to socialise and enjoy the sunlight, even in the harsh Nordic winter.
CRA worked with energy optimisation experts to develop the project’s central concept: using seawater heat pumps to convert wind, solar and other forms of power into heat, which is stored in Hot Heart’s reservoirs. The system, operated by artificial intelligence, synchronises the production and consumption of thermal energy, which helps stabilise the national energy grid in relation to fluctuating supply. The whole system is expected to cover the entire heating needs of Helsinki, estimated at 6,000 GWh, by the end of the decade, all without any carbon emissions and at an estimated cost 10% lower than today.
The project is also highly adaptable and could be replicated by other cities with similar climatic characteristics pursuing sustainable heating solutions.