Ventilation myths #4/8. It is important to blow in enough fresh air into the occupied zone!
Ventilation systems are typically designed with two main principles:
1- Exhaust from wet rooms and other areas with contaminated air
2- Supply air to occupied zones
What often gets overlooked is that one of the biggest indoor air pollutants is actually the human being — and simply blowing fresh air at people does not solve the problem.
In this setup, supply air mixes polluted and fresh air directly in the breathing zone. To ensure fresh air, the whole room’s air needs to be replaced. From an engineering perspective, this is inefficient. Humans generate heat, and in still air, a rising airflow forms above us, carrying higher CO₂ concentrations upward. The smarter approach would be to extract this CO₂-rich air directly above people and supply fresh air from zones where no pollution occurs.
Think of it like a glass of clean water: add a drop of food coloring and, unless you remove it immediately at the source, it spreads and soon you’ll need to replace all the water.
See for yourself: the photos are from a restaurant, where CO₂ levels rose above 2500 ppm during the evening. Supply air was directed right above the guests, with an added fan mixing the air further. The result? I left with a headache.