Why the Mona Lisa always smiles in the Louvre: Paris’ cooling system

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PARIS — The Mona Lisa is able to keep her famously enigmatic smile because it benefits from one of Paris’ best-kept secrets: an underground cooling system that has helped the Louvre deal with the sweltering heat Temperature records broken across Europe.

The little-known “urban cold” network meanders unknowingly beneath Parisians’ feet at depths of up to 30 meters (98 feet), pumping ice-cold water through 89 kilometers (55 miles) of labyrinthine pipes used to cool the air at over 700 locations. The plant, which uses electricity generated from renewable sources, is the largest in Europe – and chugs around the clock with a deafening noise that is completely inaudible above ground.

Paris City Hall has now signed an ambitious deal to triple the size of the network to 252 kilometers (157 miles) by 2042. This would make 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. Many parts of Europe hit 40 degrees Celsius (104 Fahrenheit) in July.

The city expands the cooling network to hospitals, schools, and subway stations over the next two decades. It’s unclear how much of the system will be operational by the time of the Paris Olympics in 2024, but it’s possible the systems will be deployed at multiple Olympic sites.

Unnoticed by millions of tourists, the pipeline is currently cooling the most emblematic monuments of the City of Light, such as the Louvre and the Quai Branly Museum. It might even help calm the spirits of excited lawmakers, as it’s being used to bring down temperatures in the National Assembly.

The program is operated by the joint venture company Fraicheur de Paris, which is 85% owned by the French state-owned energy company EDF and the rest by the public transport operator RATP. The company’s leaders praise its benefits for the entire French capital.

“If all (Parisian) buildings are equipped with autonomous installations (e.g. air conditioning), this will gradually create a very significant urban ‘heat island’ effect,” said Fraicheur de Paris’ Maggie Schelfhaut, citing the increasing heat in the cities with less vegetation that cools and more urban infrastructure that absorbs the sun’s rays.

But Schelfhaut said the pipe network could make all of Paris one degree Celsius cooler than if autonomous installations were set up across the city.

“One degree down downtown is a lot,” she added.

Three of the 10 high-tech refrigeration plants are located along the Seine and are accessed via a retractable spiral staircase that’s barely visible from the street – in something akin to the Teenage Mutant Ninja Turtles’ lair.

When the water of the Seine is cold enough, a machine catches it and uses it to cool the system’s water. The by-product heat is channeled back into the Seine where it is absorbed. The chilled water is then pumped through the system’s pipes to its 730 Parisian customers.

Paris cooling sites all use renewable energy sources such as wind turbines and solar panels. The construction of four new solar energy sites that will feed into this grid is also planned. French officials see this energy independence as particularly important given the threat posed by Russia Shutdown of energy supplies to Europe.

The Russian energy company Gazprom on Wednesday Reducing the amount of natural gas flowing through a large pipeline from Russia to Europe to 20% of its capacity. European nations are quickly look for alternatives amid fears that Russia may halt gas exports – used for industry, power generation and to cool homes – entirely in a bid to gain political clout on the bloc.

The benefits of using a cooling system that uses renewable energy for operations are already being realized by sites that use them. The world’s most visited museum, the Louvre, has benefited from the network since the 1990s – and officials are proud of its environmental, economic and art conservation benefits.

“This allows us to benefit from energy with a lower carbon footprint all year round,” said Laurent Le Guedart, director of heritage at the Louvre. “The peculiarity of the Louvre Museum is that it has to use ice-cold water to properly preserve the artworks and to control the humidity.”

The Louvre doesn’t use air conditioning, and officials say the cooling also gives them much-needed space in the sprawling but cramped former palace, which is home to 550,000 works of art.

Le Guedart said the system saves money given the rising energy costs involved Ukraine conflict. It works in particular in the state room of the Pavilion Denon, where the Mona Lisa lives. Perhaps that’s why beads of sweat never dripped down the forehead painted by Leonardo da Vinci.

“The energy bill of the Louvre is around 10 million euros per year in 2021. We try to control this bill as much as possible given the apparent fluctuations and increases in energy costs,” said Le Guedart.

The system could save him millions by cushioning the shock while Russia continues to shake up the energy market.

Jade Le Deley in Paris contributed.

The Associated Press’s climate and environmental reporting is supported by several private foundations. Learn more about AP’s climate initiative here. The AP is solely responsible for all content.

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