Faced with global warming, greening buildings is urgent. As the energy they consume in heating, air conditioning and ventilation is essentially fossil, “buildings represent 15% of total total European greenhouse gas emissions ”, underlines a report by Easac, which brings together the national academies of sciences of the Member States of the European Union .

His document identifies avenues to enable Europe to meet its objective of lowering its greenhouse gas emissions by 55% in 2030 and achieve carbon neutrality in 2050. First observation: 85% to 95% of 225 millions of Existing European buildings will still be in use in 2050. They must therefore be renovated to improve their performance, especially since 30% of the fleet is already over 50 years.

But to treat energy-inefficient buildings by 2030, EASAC estimates that it would be necessary to renovate 2 % to 2.5% of the fleet per year during 15 years, compared to 1% per year on average currently. Which seems unrealistic.

85. 000 renovations per week It’s even more complicated for the residential part of the park. The 195 millions of residential buildings existing in 2019 in the Europe of 27 consume on average 170 kilowatt-hours (kWh) per m 2 and per year and are heated mainly with gas. We should get out of fossil fuels. But renovate by 2050 the 62% of the least energy efficient fleet would mean 146 millions of renovations on 25 years, or “a rate of renovation of the park European residential by 2.2%. Concretely, this implies renovating more than 85. 000 accommodation per week ”, recognizes Easac. A pace that is again difficult to achieve.

One thing is certain: for this council of scientists, we must dust off the concept defined by Brussels of a “quasi-passive” building, which is based only on on energy performance, to replace it with the notion of a building with “almost zero emissions” of greenhouse gases.

Building with “almost zero emissions” What will this building look like? It will be built in low carbon materials, will be very well insulated, will produce (and store) renewable energy, including for its domestic hot water, will be equipped with a heat recovery system, as well as efficient heating. and low emissivity, therefore more at the scale of a district than an individual – because, for Easac, the heating network is the future – and finally of an air conditioning to match.

On this last point, it is not won, in view of worldwide sales of air conditioners . Carried by the heat waves, they climbed by 000% of 2018 to 2018, drawn by l ‘Asia and the United States, underlined last year a report from the International Energy Agency (IEA) which anticipates a further increase in the world fleet of two-thirds by 2030.

The need for energy related to air conditioning has tripled since 1990 and the two billion air conditioners in the world (two-thirds residential, or one for every five inhabitants) represent 10% of peaks in electrical demand. Worse: the majority of air conditioners sold today are two to three times less efficient than the most efficient, denounced the IEA last year by advocating the imposition of energy efficiency criteria.

The cooling district is taking off For the time being, in Europe, air conditioning still only represents 0.4% of the energy consumption of the residential stock, but here too demand is rising and consuming energy, based on air-to-air heat pumps. Easac, like the AIE, recommends anticipating by providing residents with high-performance and carbon-free collective systems, such as “district cooling”, a network built on the scale of the district or the city circulating to the inside buildings naturally cold water (taken from the groundwater, the sea or a stream) to refresh them. The practice “has proven to be a very efficient cooling system”, underlines the IEA. It is expanding in Scandinavia and Germany, where installed capacity has increased by 55% of 1990 to 2011, and exists in Paris, as in London and Barcelona.

It remains, in France, to develop this technique, among others, to green buildings. Because the energy consumption of French residential (a little more than 170 kWh / m 2 / year), although it is lower than in Belgium and Germany, remains higher than the European average (170 kWh / m 2 / year) and that of the parks British, Spanish and Italian.

The “wave of renovation” desired by Brussels would require 195 billion euros per year While new buildings can achieve virtual carbon neutrality at a cost deemed acceptable for private investors, the same cannot be said for renovations of existing buildings, including the cost may require thirty years to be amortized by energy savings.

The “wave of renovation” proposed by Europe in 2020 would consist of renovating 3% per year of a fleet of 15 billion square meters by 2050. At an average cost of 250 euros / m 2 , this renovation would represent 225 billion euros per year, notes Easac. Most of it would be covered by private financing, but deriscated and accelerated by public incentives. The European Parliament has proposed a subsidy of 100 euros / m 2 for ambitious energy renovations, i.e. 62 billions per year.