It is important for humans and other living organisms to have proper ventilation in order to maintain a clean indoor air quality. The fact that indoor air is not cleaner than outside air has been proven by many kinds of research through testing and measuring. In fact, ventilation, a method of bringing the outdoor air into the indoor environment, is the most affordable way of cleaning indoor air.

However, during ventilation, the indoor cooling or heating energy is lost. So it is very important to minimize energy loss while ventilating appropriately in order to maintain a comfortable environment.

There are various hazardous substances that are used as reference substances for ventilation such as VOCs, dust, formaldehyde, etc because CO2 is emitted in a large volume by humans and animals and when fuels are burned. Through various studies and verification, CO2 is regarded as reference gas for detection of harzardous gas and to check if air became clearly or not through ventilation.