A prerequisite for the establishment of a ventilation system is where it should be possible to receive fresh air for ventilation and where to dispose of used air.
Ventilation air must be treated before blowing: filtration, air heating, air cooling, humidification, air drying or, in special cases, sterilization. This air treatment was carried out in air-treatment units built of masonry structures. Modular air handling units are common. The air handling unit is assembled from these cabinets according to the desired air quality and air volume.