How compressed air is inspiring architects

Compressed air hasn't run out of breath! An American start-up has been working for five years on a motor-compressor that minimizes the side effects of compression while improving yield in order to produce four different types of reusable energy. This is a development that has opened up some bright prospects and opportunities to innovate for architects, who now work on buildings capable of achieving global performances, rather than on the "simple" notion of dwellings.

The renaissance of an old technology

One century ago, compressing air to power trams, like in the French cities of Nantes and Paris, was a common practice. Compressed air offered a number of significant advantages: No emissions of fumes in the city, no electric cables above the locomotive, etc. But to produce air compressed to 80 bar, at that time, it was necessary to burn large quantities of coal in special power plants**. So the environmental balance was not that good after all. Nor was the safety of the vehicles, which had to cope with the thermal consequences of pressurising and expanding the air, including severe releases of cold on the mechanical parts. So these motors, which had a yield of just 30 percent to 40 percent, gave way to the solutions that we know today.

But when your name is Danielle Fong and you graduated from high school at the age of 14, then from Dalhousie University at the age of 17 and became the youngest ever member of the MIT TR35* in 2012, you don't let this kind of detail get in the way. And especially when the issues of human health, natural resources, climate change and the environment in general, are more serious than ever before. So in 2009, this young Canadian gave up her studies in nuclear fusion, a solution she felt was still too far off in the future, to create the LightSail Energy start-up, on the basis of a patent for a motor that converts electricity into compressed air, so that the driving force of the air can then be converted into four different forms of energy: heat, cold, electricity and mechanical force. All without any thermodynamic consequences and with very high efficiency: 77 percent in the compression and expansion phase, by recycling the heat and the cold in the compression chamber. This is the patented R.A.E.S., or Regenerative Air Energy Storage, technology.

This innovation does not demand any particular geographical conditions - air is everywhere! - it does not pollute and can use electricity from renewable sources. It has already convinced several investors, including Bill Gates. Total Energy Ventures was one of the very first venture capital investors, which ploughed $57 million into the start-up: a decision in keeping with the group's Better Energy vision.

From trams to buildings

But Total wasn't the only company to show an interest in the development of compressed air technology. The Nantes-based architects AIA also saw it as an opportunity to solve the problems of the city of the future and its eco-districts. Since this company was founded 50 years ago, it has always tried to generate synergies between the art of architectural and the rigour of engineering. Two worlds that are often, and wrongly, perceived to be in opposition.

Laurent Rossez, Director of Strategy and Innovation at AIA, claims that "this hybrid vision of architecture will allow us to build or renovate, while taking account of not only the environmental constraints of the urban world, but also of the demands of our future customers, such as digital inclusion and energy transition. Architects already have the right answers to these challenges."

The company studied many energy storage and distribution technologies that can be integrated into housing units: electrochemical, water storage, batteries, electromagnetism, flywheels, etc. "But none of them offered as many advantages and the level of safety of compressed air," explains Rossez.

"The idea is to integrate this technology in buildings without penalising them. On the contrary, by adding value through the use of the available empty spaces." This is the Air4Power concept. "4", for the four types of energy that can be used in residential and tertiary buildings.

Heat: it is generated when the air is compressed and can be stored at 87 degrees Celsius in the lower parts of the building. In this case, there must be no foundations in the ground, which demands a floor capable of distributing the loads. These floors are thicker than usual and have cavities, in which cold water and air can be stored.

Cold: it can be distributed through the building for air conditioning purposes, but can also replace cold appliances - fridges and freezers - by creating cooled cabinets.

Compressed air: it can perform all or part of the mechanical functions, such as powering the elevator machinery, or fuel a fleet of vehicles that uses this energy.

Electricity: when the compressed air produced during the daytime by renewable energies is expanded in the evening, it can power electric generators at the right time of day, or be connected to local micro-networks.

In Rossez's opinion, "the possibilities are endless. Every solution offered by this clean, light and safe technology is a source of creativity and innovation in a sector that is calling out for them. "

What about safety?

When we ask Rossez about the safety of a residential building sitting on a floor of air compressed to 200 bar, he reminds us that, "We already live with pressure. The recharges used to produce fizzy water at home are at 250 bar, SCUBA divers' oxygen tanks are at 200, gas has been available in towns and cities for a long time already, and some of the trucks on our roads are filled with inflammable liquids pressurised to more than 200 bar." It's a risk that is under control, especially since LightSail Energy has tested carbon fibre tanks at 600 bar, or three times the maximum working pressure, some of which were torn open, but did not explode.

"We've been looking for a highly integrated solution for a long time. This solution will demand strict risk management and will be certified by the European labels. Until then, we already have numerous applications to develop, which are less integrated, such as the countless empty, classified buildings that are being put to new uses. Our technology can be used in available spaces, without any major works," concludes AIA's Director of Strategy and Innovation.

* List drawn up by the MIT of the best innovators aged under 35 in their Technology Review

** Like the former Sudac premises, which are classified as historical buildings and have now become the Paris-Malaquais school of architecture.

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