The ventilation of buildings is used to maintain indoor air quality and thermal comfort. In order to attain these objectives, airflow rate should be controlled. The minimal airflow rate is determined by indoor air quality requirements so that the maximal concentration for every pollutant is lower than the maximum admitted. By changing the airflow, comfort may also be controlled. Thermal comfort is influenced by air parameters (e.g. temperature, humidity, velocity and turbulence) and surface temperatures (of walls, windows, etc.), but also by the type of human activity and clothing. Recent studies show that in naturally ventilated buildings, occupants adapt themselves to the indoor climate, accepting a wider range of indoor temperatures as comfortable.