The Helsinki Energy Challenge has given the architecture industry an opportunity to overhaul the way the city operates, in an attempt to lead the way as a sustainable city with a new, environmentally friendly urban heating system.

With 252 teams from 35 countries entering the challenge, four winners were selected for their plans, with many engineers, architects and tech start-ups vying for selection. The winning projects will be adopted by the city within the next decade, as Helsinki looks to be completely carbon-neutral by 2035.

Carlo Ratti Associati, who have proposed creating island-esque sea water reservoirs that store heat in an effort to decarbonise the heating network, have been announced as one of the competition’s winners.

Dubbed Helsinki’s Hot Heart, 10 floating reservoirs would act as a mini archipelago. Seawater heat pumps are used to convert energy from wind and solar power to heat. The energy would then be stored within the ‘islands’, with groups of the reservoirs working together as one large thermal battery to store heating that would be available to the city’s regions during the winter.

Carlo Ratti Associati aims to create four reservoirs that will double as recreational spaces, with the heat of the collective reservoirs allowing for tropical plants to be housed within an area that the general public can visit.

Developed in partnership with Squint/Opera, Ramboll, Transsolar, Danfoss/Leanhear, Schneider Electric, OP and Schlaich Bergermann Partner, Carlo Ratti Associati hopes for the project to be implemented in 2028.

Smart Salt City, designed by SaltX Technology and Rebase Energy was another winner in the challenge. Using artificial intelligence to monitor demand and supply forecasts, Smart Salt City relies on renewable energy sources for heat.

Another winning design was HIVE, a project that centres around the installation of heat pumps in the Baltic Sea, developed by a consortium of energy companies, including Storengy, Newheat and Engie.

The project would see 50% of Helsinki’s heating requirements solved by the heat pumps, that would also use thermal fields and energy storages, as well as district heating optimisation.

Beyond Fossils was the fourth winning project. Described as an “energy transition management model”, it proposes that Helsinki opts for clean heating by 2029, through holding clean heating options where energy developers bid against each other to supply the city with energy. The project was overseen by VTT, Hansel and the Finnish Environment Institute.

All four winners received €250,000 for their efforts in looking to help Helsinki reach its targets. The organisers say they hope to be a visionary for other cities around the world looking to make the switch to clean energy, and how they might do so. 

"Helsinki is not alone: to fight climate change, sustainable heating solutions are needed in cities all over the world – heating not just beyond coal, but also beyond burning biomass," a statement says.

"The City of Helsinki is committed to sharing the lessons learned and results gained in the competition so that also other cities around the world can use them in their climate work."

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