What if all buildings produced more energy than they consumed? What if rethinking the way buildings are designed and built was one of the main keys to sustainable urban development?

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As the World Economic Forum (WEF) points out, buildings alone account for 39% of global greenhouse gas emissions (11% in materials and construction and 28% in operating emissions). Knowing how to build and operate buildings that have a low impact on the environment will be crucial to achieving the objectives of the Paris climate agreements.

Many efforts have already been made in this direction, with success. In particular, buildings producing more energy than they consume (known as "positive energy buildings", sometimes abbreviated as "BEPOS", positive energy buildings) are multiplying in several places in the world and demonstrate that a building can also be ecological.

Norway at the forefront

The Powerhouse Brattørkaia, an eight-storey building in Trondheim, Norway, is often cited as an example. Completed in 2019, it houses 18,000 m² of office space, a mezzanine and underground parking.

Everything, from the initial design to its construction (or subsequent demolition), has been designed to reduce the energy and environmental impact of the building. The building thus takes advantage of a set of innovative technologies and principles to radically reduce daily consumption: air circulation to reduce the need for heating, heat recovery, recovery and treatment of gray water, use of sea water to heating and cooling, use of particularly energy-efficient electrical appliances... The structure of the building itself, based on low-emission concrete, is exposed through strategic cutouts in the ceiling. "The mass absorbs and retains heat and cold and helps regulate the temperature in the building without using electricity," explain the architects of the project.

In addition, thanks to its roof covered with nearly 3,000 m² of solar panels, the building produces around 460,000 KWh per year. And the result is convincing: "On average, the building produces more than twice as much electricity as it consumes daily and supplies itself with renewable energy, while supplying neighboring buildings or electric buses. , cars and boats via a local micro-grid”.

Powerhouse, which brings together five Norwegian companies and organizations and gave birth to Brattørkaia, has produced several other such 'climate buildings' in the past, including a school occupying 900 m² and producing 30 500 kWh per year (Montessori school in Drøbak) or even a renovated old building (in Sandvika) generating up to 21 kWh of energy surplus per square meter of living space.

Another project, initially led by Powerhouse before being acquired by Miris, was recently publicized: Svart, a luxury resort intended to become the first entirely self-sufficient hotel in the world. Initially planned for 2021, the construction site was delayed (notably due to the Covid crisis) and the hotel should open in 2023.

Built on a fjord, on the edge of the second largest glacier in Norway (Svartisen, inside the Arctic Circle), the circular hotel will adopt radically ecological biases: more or less concrete, steel , aluminum or bricks (replaced in particular by wooden and stone pilings), sustainable vegetable garden and fish farming on site, recycling of wastewater, capture and recycling of the heat given off by the kitchens, etc.

Solar panels will power everything, with the aim for the hotel not only to be totally disconnected from the grid but also to supply its surplus electricity to local communities or to power a fleet of electric boats circulating around the resort. "Svart will demonstrate that the contemporary traveler can contribute to the sustainable growth of our planet without sacrificing the conveniences and comforts of modern life", assure the promoters.

Eco-friendly buildings

The idea is therefore gaining ground and, in addition to Norway, there are similar approaches and examples of positive energy buildings around the world.

For example in Germany, as noted by the German Council for Sustainable Real Estate, a good fifteen pioneering buildings in this area have emerged in recent years, whether office buildings, bank branches, schools or individual houses. All use innovative processes to achieve energy neutrality and reduce environmental impact: new materials, new principles of insulation and circulation of heat flows, new modes of energy storage...

Same thing in France, where dozens of BEPOS-approved buildings have emerged, including some are emblematic, such as the Descartes+ building of the Ecole Nationale des Ponts et Chaussées, one of the oldest (inaugurated in 2012) and which produces 32% more energy than it consumes. Or like Hangar 108 in Rouen (Hôtel de la Métropole Rouen Normandie), commissioned in 2017 and still the largest positive-energy building in France (8,000 m²). At the beginning of September 2021, an unprecedented real estate project was also announced in Dijon: the first positive energy social housing. Built "at standard costs" on a plot of 2,300 m² and on three floors, the building "will produce more energy than it will consume, thus allowing its inhabitants to have an energy bill close to zero and therefore a significant gain in purchasing power and comfort”.

Another example in Singapore, where the National University campus now houses several positive energy buildings, including the SDE4, finalized in 2019, which uses an innovative air conditioning device and houses 1,200 solar panels generating 500 MWh of energy. energy per year. The university estimates that this building alone saves $180,000 in electricity annually.

We are beginning to see the real benefits of all these approaches. In the United States, Unisphere, fully operational since 2019 and considered the largest negative energy commercial building in the country, underwent a comprehensive audit last year, in particular to measure its energy relevance. The six-storey building, which houses the headquarters of a biotechnology company, uses 3,000 solar panels, but also a complex and unique geothermal system: 52 wells dug 150 m deep, together with a circulation coolant, hydraulic heat pumps and an indoor swimming pool serve both to heat and cool the premises.

The audit sheds light on the actual data, after one year of operation: "The total energy consumption of the building is around 6% lower than predicted, but the solar production is also lower by around 22% than expected. Even so, with a total output of 915 MWh, “the building was still able to meet the zero energy goal, despite having lower than expected renewable energy sent back to the grid”. Adjustments and optimizations (both thermal systems and lighting and other electrical systems) continue to be made, but the principles implemented have already proven themselves. "Unisphere's performance data shows that these types of buildings — if designed, constructed and commissioned appropriately — can perform as intended and are not just theoretical studies," it concluded in October 2020. .

Digital to the rescue

As we can see, the challenge is not just to install solar panels on the roofs or to include green walls on the facade of buildings, but to rethink — from A to Z — the way buildings are designed, constructed and used.

For the World Economic Forum, we can identify "four crucial trends" which are all vectors on which to act to achieve zero carbon buildings: decarbonization, electrification, energy efficiency and digitization. All must be skilfully combined to reduce emissions and limit the environmental impact of buildings.

And in all of this, digital plays a special role. Electronic sensors and automatic systems integrated into buildings are far from being gadgets, but one of the keys to optimizing resources. By going digital, buildings become “smart buildings” and “they take advantage of advanced sensing and control systems, data analytics and energy optimization to actively reduce energy consumption and demand. energy, while improving on the one hand the comfort, health and productivity of the occupants, on the other hand the resilience of the installations", notes the Forum.

And the contribution is significant. “Basic automated controls can save 10-15% energy in commercial buildings,” says the WEF, while “demand-based ventilation control systems can add 5-10% savings,” while such as digitized control of heating and lighting, sufficient to result in additional energy savings of 8-18%. Added to automated systems for detecting breakdowns or promoting diagnosis, or to devices for optimizing the use of electricity (produced in situ or coming from the grid), we understand that digital technology applied to the management of buildings is “a crucial element in ensuring the efficiency and zero carbon footprint of buildings, while reducing investments in electricity grid infrastructure – a top priority if we are to meet the 2050 targets”, concludes the WEF.

This confirms, if need be, that reducing the environmental bill of buildings requires technological innovation. By rethinking the construction and operation of buildings, inventing new materials and relying on the full panoply of digital tools available (IoT, Big Data, Artificial Intelligence, blockchains, etc.), the path seems clear. towards constructions that no longer damage the planet but become its complementary lungs. For buildings as for many other things, real ecological solutions exist, without sacrificing comfort and modernity.