Europe’s largest cooling network serves sites across the city, including buildings that will be used for the Paris Olympics next summer, such as the Grand Palais, a sprawling glass and steel exhibit hall in central Paris.

It draws water from the River Seine for cooling power stations that pump cooled water through underground pipes to buildings that use it instead of individual air conditioning units, said Nayral of the network operated by Paris Fraicheur, which is 85%-owned by French energy company Engie and 15%-owned by Paris transport operator RATP.

“The buildings pick up the coolness of water that we deliver and will use it for air-conditioning,” she said, in what she stressed could help control the level of air-conditioning carbon emissions in Paris.

Plans are to develop the system in southern parts of the city, as well as extend it to hospitals, daycare centres, and retirement homes, she said.

The aim is to triple the network to about 250km by 2042.

Like many cities in Europe, Paris has had extremely hot summers in recent years, with temperatures rising as high as 43 °Celsius in July last year.

Ghislain Tezenas Du Montcel, owner of an office building that uses the underground cooling system, said the new system was more sustainable, and also beneficial financially.

“Given the fact that the price of electricity has increased, we think (air-conditioning via this network) is now cheaper,” said Tezenas du Montcel.