In La Défense, the largest office tower in Europe saves electricity

"Energy efficiency has been talked about for three or four years," explains technical director Ludovic Levavasseur, 52, who is supporting the change, already well underway with nearly 40% less consumption between October 2021 and October. 2022.

Invisible on the bill, because the price of kWh has increased in parallel, the decline will continue, he assures, in particular thanks to the thousands of presence detectors gradually installed in the 170.000 m2 of offices.

Hour by hour, day after day, these automatons communicate with the computer of a modest blind room in the basement where Nicolas Puype, 42, monitors. An employee of the maintenance provider Engie Solutions, he has been the building's "energy manager" for three years.

Six to 7.000 people work in the seven buildings of Cœur Défense, with a downward trend linked to teleworking.

Without seeing them, Nicolas Puype witnesses the ballet of their arrivals and departures, instantly transmitted to the building's technical management system (GTB).

"I know almost everything that happens, without moving, I don't even need a camera", confesses the automation engineer who goes so far as to guess which train people took to reach the business district.

On its screens, the elevators go up, the lights come on, the fan coils start up, and the electricity consumption curve climbs, then collapses at the end of the day.

When a desk is unoccupied, it is automatically turned off.

Nicolas Puype does not dictate the temperature, nor does he regulate it from a distance, but he has an eye.

On a screen to his right, all energy production is synthesized, the slightest anomaly reported. Color graphs are superimposed, the consumption of the day, that of the day before.

All the sensors at Cœur Défense, and the computers that Nicolas Puype monitors, have an ultimately simple mission: to heat and light only when the workers are present. "If you already consume only what you need to consume, you are safe," comments Thierry Chambon, CEO of Energisme, a company that sells energy management software.

All electric

The skyscraper, recognizable by its two 40-storey towers with rounded edges culminating at 161 meters and its bay windows forming a changing white checkerboard, is 80% occupied.

Impossible by definition to stop the heating or the air conditioning, nor of course to open the windows.

To breathe, it is necessary to pulsate new air, hot or cold depending on the season, to supply 42.000 lighting points, 76 elevators, 11 escalators, 14.000 blinds, more than 8.000 fan coils, etc.

Everything is electric. Safety generators start in the event of a cut. The electricity bill is therefore the second item of expenditure for the tower, after security and fire safety.

And at a time when prices are soaring, the man for the job is Mr. Puype: "Here it's a liner. Once it drifts, to catch up it's a bit late, it's That's why I watch day by day," he said.

In 2021, the building replaced its six heat recovery chillers. A material that produces all the heat and cold that the tower needs, the urban network only serving as a backup.

This equipment dated back to the inauguration in 2001. New, it is more efficient and it is this investment that has enabled the spectacular drop in electricity consumption last year.

For next year, the expected drop, from 10 to 15%, will be less easy: "We will try", assures Frédéric Galvez, deputy general manager Property Management at BNP Paribas Real Estate which manages 2.000 buildings in France, including Coeur Défense .

The insulation remains. "It would be a colossal, monstrous investment, costing almost the price of the building (bought 1,8 billion euros in 2017, editor's note)", he says. "This would require the entire hull to be removed, the tenants to leave and the owner to have no income during the construction".

For the time being, the tower is rather thinking about equipping itself with photovoltaics.