Microsoft heats Finnish homes with data centre heat

In Mäntsälä, Finland, a data centre heats two thirds of the inhabitants. The town, just north of Helsinki, was the first to realise in a big way the idea of a local engineer, Ari Kurvi, who has a penchant for recovering waste heat from data centres. Since it went into operation a decade ago, Nebius Group's data centre has radically cut energy costs for residents. Now its idea is spreading and some of the world's largest technology companies are turning to heat recovery from data centres in an effort to become more sustainable. The largest project in the world is the one started by Microsoft just outside Helsinki: a cluster of data centres that, when completed, will provide heating to 100 thousand homes, 40% of the needs of Espoo, Finland's second largest city. Nokia's home country is aiming for carbon neutrality by 2030 and has already shut down a coal-fired power plant because it is no longer needed.

With a harsh climate and an electricity grid dominated by renewable sources - hydroelectric and wind power - the Nordic countries have become a magnet for technology companies. Here, data centres can often be cooled simply with outside air, reducing energy consumption. Another advantage is that electricity prices in the region are low, but the most interesting aspect is the ubiquity of district heating systems. These networks are extremely energy-efficient, especially when fed by infrastructure that generates a lot of waste heat, such as a metro or a large data centre.

In the Espoo plant, which Fortum is building on the Microsoft campus to start up by the end of the year, heat from the data centres will produce warm water between 25 and 35 degrees Celsius, which will be fed into a recovery system equipped with some 40 water-to-water heat pumps. The pumps extract the heat, sending water at 86°C to two large electric boilers. These raise it to 115°C, a temperature sufficient to heat the houses. The possibility of using district heating (which has been in operation since 1954) was the reason why Microsoft built its first Finnish centre here. "These data centres are actually big fans, which allow electricity to be converted into cheap heat, which is not trivial: it is easier to produce zero-emission electricity than zero-emission heat," comments Kai Mykkanen, Mayor of Espoo and former Finnish Climate Minister.

Other important waste heat recovery projects are underway in Sweden and Ireland. South of Stockholm, for example, Conapto opened its fourth and largest data centre last year: the 20 megawatt plant feeds the city's district heating system with excess heat energy, which distributes it to 10,000 homes. Despite the potential of this technology, however, there are limits to its application, first and foremost the geographical discrepancy between data centres and district heating systems, which are concentrated in urban centres where land prices are higher. In Norway, the installation of data centres deep in the woods - like a gigantic Google project south of Oslo - faces strong opposition precisely because of the lack of consumers in the vicinity.

It is predicted that the heat available from data centres in Europe will reach at least 200 terawatt hours per year by 2050 (and possibly sooner), four times more than today, according to Brian Vad Mathiesen, professor of energy planning at Aalborg University in Denmark: "Obviously not all of this heat can be reused, but parameters should be imposed on data centres from the time they are built. In Germany, a new energy efficiency law will have an impact on the development of recovery technologies: the regulation requires the largest data centres to use 10 per cent of waste heat from 2026, and 20 per cent from 2028. The fact remains that heat recovery does not make data centres good for the climate, only less harmful.