Colder and less polluting: an "air conditioner of the future" designed in Caen

"Our targets are overheated urban areas", explains Julien Cardin, 49, teacher at the National School of Engineers (ENSI) in Caen and engineer at the University of Caen Normandy.

"Air conditioners warm the atmosphere less locally (by creating heat islands around the building, editor's note) than globally through the emission of CO2", he underlines.

The structure in question, called "cooling radiative surface" (SRR) and placed on a roof, reflects the visible rays of the sun so as not to heat the construction and evacuates the internal heat by infrared radiation towards space without heating the atmosphere.

For better efficiency, the device can be connected to a heat exchanger supplied with coolant fluid, water for example, by a pump, which consumes much less energy than current systems.

"Very good ideas", greets Céline Laruelle, engineer in the building department of Ademe joined by AFP.

For the time being, "air conditioning still has a fairly limited impact" on climate change, according to her. "France still has a reasonable rate of equipment, but without changing behavior, without renovation of the building, it could become very impacting by 2050".

According to the report "Comfort air conditioning in residential and tertiary buildings in 2020" supervised by Ademe, air conditioners consumed 15,5 TWh (3% of production) and emitted 4,6 million tonnes of CO2 equivalent. that year in France, mainly due to refrigerant gases.

The SRR is made up of discs of a few centimeters of silica and oxide of a metal called niobium, manufactured by a machine from the Turin firm (Italy) Elettrorava.

Up to "30 degrees" less

This is one of the strengths of the project: "Stanford University in the United States is developing the same project (called "Skycool", editor's note) but with critical or unsustainable materials, we made the opposite choice, sustainability and non-environmentally and human rights-friendly sourcing,” says Cardin.

"We were aiming for 10 degrees, but the theoretical performance of reducing the temperature inside a building is 30 degrees, or 110 watts per m2" exults the engineer, "for 33m2 of SRR on a roof, we equal with 100 watts the performance of a heat pump that consumes 1.500".

Artificial intelligence has given it a serious helping hand.

"I wrote evolutionary algorithms to model our experiments" with spectacular success: "in three hours the algorithm found a design that worked when we had tried for two years without success", explains the researcher.

Effective today in the prototype state, the project is of interest to industrialists, with a winter version in the boxes: "we know how to be cold when it's hot, we just have to keep warm when it's cold", says the teacher.

To finance the research of this winter version, it will take money: supported by the CNRS via its Peps energy program, by the Norman laboratory of excellence LabEx EMC 3 financed by the State as well as by the Normandy region, Mr. Cardin is in negotiations to finance this thesis, and even other applications.

"This technology can be used for thermal camouflage, to make solar panels durable, off-grid refrigerators, temperature-regulating clothing..." advances the scientist.