Cooling Buildings Naturally, Through Rivers and Lakes

Cities around the world are increasingly utilising river- and lake-fed systems to cool buildings, reducing energy consumption and helping combat urban heat.

“People are so proud of this project,” says Fengqi You, professor in energy systems engineering at Cornell University, speaking of Lake Cayuga’s lake-source cooling setup.

The system works by pumping naturally cold water from deep in rivers or lakes through heat exchangers, which transfer the chill to a separate closed water loop that circulates through buildings. The cold source water never mixes with the building system — it simply absorbs heat and then returns to the lake or river. In Paris, the Seine river cooling network already covers 100 km of piping and serves about 800 buildings, with plans to expand to 245 km and 3,000 buildings by 2042. Cornell’s system pulls water roughly 76 meters deep from Lake Cayuga, staying near 4°C year-round, and provides about 98% of the campus’s cooling load with very high efficiency. These systems conserve energy, reduce heat released into the city air, and offer scalable models for staying cool in a warming world.