The city of Paris plans to expand an urban cooling system that draws on water from the Seine river as it seeks to meet rising demand for air conditioning while curbing carbon emissions, its secretary general Raphaelle Nayral said.

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

It draws water from the Seine River 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, owned 85% by French energy company Engie and 15% 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, day care centres and retirement homes, she said. The aim is to triple the network to about 250 km (155 miles) by 2042.

Like many cities in Europe, Paris has had extremely hot summers in recent years, with temperatures rising as high as 43 degrees Celsius (109 degrees Fahrenheit) 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.