A cool secret that can help Mona Lisa smile

The Mona Lisa is able to keep her famous enigmatic smile because she uses one of Paris’s best-kept secrets: the underground cooling system that helped the Louvre weather the sweltering heat that broke temperature records across Europe.

A little-known network of “urban chill” snakes under the feet of unsuspecting Parisians up to 98 feet (30 m) deep, pumping icy water through 55 miles (89 km) of labyrinthine pipes that are used to cool the air in more than 700 locations.

The system, which uses electricity generated by renewable sources, is the largest in Europe and operates around the clock with a deafening noise that is completely inaudible above the ground.


Pressure gauges on one of Fraicheur de Paris’ underground cooling pads (Lewis Joly/AP)

Paris City Hall has signed an ambitious contract to triple the size of the network by 2042 to 157 miles (252 km), making it the largest urban cooling system in the world.

The new contract aims to help the city adapt to and combat the threat of global warming. Temperatures reached 40°C (104°F) in July in many parts of Europe.

Over the next two decades, the city will expand the cooling network to hospitals, schools, and subway stations.

It is not yet clear how much of the system will be operational in time for the Paris 2024 Olympics, but it is possible that the systems will be used at multiple Olympic venues.

Unknown to millions of tourists, the pipeline is currently cooling the most emblematic sites in the City of Light, such as the Louvre and the Quai Branly Museum. It may even help to cool the temper of anxious politicians, as it is being used to bring down the temperature in the National Assembly.


The Louvre capitalizes on an underground cooling system, one of Paris’s best-kept secrets. (Lewis Joly/AP)

The scheme is operated by the Fraicheur de Paris joint venture, which is 85% owned by state-owned French energy company EDF and the rest by public transport operator RATP. Company officials advertise its benefits to the entire French capital.

“If all (Parisian) buildings were fitted with stand-alone installations (such as air conditioners), this would gradually create a very significant urban heat island effect,” said Maggie Schelfhout of Fraicheur de Paris, referring to increased heat in cities due to less cooling vegetation and more urban infrastructure to absorb the sun’s rays.

But she said the pipe network could make all of Paris 1C (1.8F) cooler than if off-grid installations were installed throughout the city.

“One degree less in the city center is a lot,” she added.


Maggie Schelfhout of Fraicheur de Paris climbs the stairs to visit one of the company’s underground cooling centers. (Lewis Joly/AP)

Three of the 10 high-tech cold stores are located on the banks of the Seine and are accessed by a retractable spiral staircase barely visible from street level, somewhat reminiscent of a ninja turtles’ lair.

When the water in the Seine gets cold enough, the machine catches it and uses it to cool the water in the system. The heat generated as a by-product is returned to the Seine, where it is absorbed. The chilled water is then pumped through the system’s pipes to 730 customers in Paris.

All Paris cooling facilities use renewable energy sources such as wind turbines and solar panels. It is also planned to build four new solar energy facilities that will be included in this network.

French officials see this energy independence as particularly important given the threat of Russia cutting off energy supplies to Europe.

The Russian energy corporation Gazprom on Wednesday reduced the volume of natural gas passing through the main gas pipeline from Russia to Europe to 20% of its capacity.

European countries are rushing to find alternatives amid fears that Russia may completely cut off exports of gas used in industry to generate electricity and cool homes in an attempt to gain political influence in the bloc.

The benefits of using a cooling system that uses renewable energy to operate are already being felt in facilities that use them. The Louvre, the world’s most visited museum, has been using the network since the 1990s, and officials are proud of its environmental, economic and artistic benefits.


Map of operating sites Fraicheur de Paris (Lewis Joly/AP)

“This allows us to benefit from energy with a lower carbon footprint, available all year round,” said Laurent Le Guédard, director of heritage at the Louvre. “The peculiarity of the Louvre Museum is that for the proper preservation of works of art and control of humidity, it is necessary to use ice water in it.”

The Louvre does not use air conditioning, and officials say the refrigeration also gives them much-needed space in the sprawling but cramped former palace that houses 550,000 works of art.

Mr. Le Guedard said the system saves money given the rising cost of energy associated with the conflict in Ukraine. He works, in particular, in the main hall of the Denon Pavilion, where Leonardo da Vinci’s Mona Lisa lives.

“The energy bills for the Louvre are around 10 million euros per year in 2021. We are trying to control this bill as much as possible against the backdrop of obvious fluctuations and increasing energy costs,” said Mr. Le Guedard.

The system could save millions by cushioning the shock as Russia continues to disrupt the energy market.