Knowing that the buildings are the largest consumers of energy in the country, the legislator has put in place different instruments: tax incentives for renovation for old buildings (the most fuel-consuming), thermal regulation for New buildings (the last in force being the RT2012) and for the first time a regulation for the larger existing tertiary buildings thus obliging them to renovate them.

The successive thermal regulations have first privileged the insulation of the casing and then its air -tightness, passing through the heating with improved efficiency (condensation and heat pumps). Since the RT 2012 new buildings are therefore "air-tight" which requires a mechanical or natural controlled ventilation.

Indeed, a well insulated building mainly loses calories through the release of warm air in winter or fresh air in summer due to ventilation. Heating and air conditioning consumption then becomes mainly related to the flow of renewed air.

It is therefore necessary to control the air renewal in order to minimize energy consumption . But first of all, we must ask ourselves the main question: Why do we need to renew the air in buildings?

Our brain functions distinguish us from other mammals, the brain is our most precious heritage. This, even if it only represents 2% of the weight of our body consumes alone 20% of the oxygen of the air breathed through the blood flow. And the blood also provides other foods to the brain which it nourishes with frugality.

Breathing is similar to combustion: we inhale oxygen that our lungs assimilate and which is transported thanks to haemoglobin, but they also reject the oxygen that has been consumed (oxidation) in the form of CO2 and water vapour (H2O). The volume breathed in a single day represents a volume of 15m3 of air. The developed surface area of our lungs is about the size of a tennis court. This gigantic surface is very porous and absorbs, in addition to oxygen, Volatile Organic Compounds (VOCs) and fine particles contained in the air. If these elements were not absorbed, the bottom of our lungs would be as dirty in one day as the bottom of our bed after a month. For example, by breathing in alcohol vapours (one VOC among others), you can quickly become drunk, not to mention the drugs you inhale.

All these elements absorbed by respiration are conveyed by the blood to feed mainly our brain.

This is why poor indoor air quality impairs cognitive function, productivity and health.

For example, a concentration of 1,000 ppm CO2 (the air we breathe out), which is the regulatory threshold for an school classThe results of the study show a reduction in cognitive functions of more than 23%. When you know that in a school class Since it is common to reach more than 3,000 ppm after one hour of class, it is not surprising that students perform poorly. High CO2 levels are also reached in a bedroom with a closed door, which affects the quality of sleep.

While CO2 has no health impact (except at extremely high levels), VOCs and fine particles do affect health. Fine particles alone are responsible for more than 48,000 deaths a year in France. VOCs are harmful overall but some are now subject to specific regulations for establishments receiving the public (ERP) because they are recognized as proven carcinogens: formaldehyde and benzene. Formaldehyde is found in wood (natural) but mainly in glues (chipboard). Benzene is found in some plastics and in gasoline fumes (replacing lead). The cases where benzene is the most important concern parking lots connected to the dwelling.

For these different reasons it is therefore essential to ventilate the buildings, but the dilution with the outside air is not always the optimum solution both in terms of energy and quality.