Mechanical (air-conditioning) ventilation systems and equipment in the food industry may transfer various pathogenic bacteria causing, for instance, pneumonia (Legionellosis). Microclimate parameters in manufacturing shops felt by people are affected by: human factors (health, individual temperature perception etc,) and non-human factors (air physical parameters, air freshness and cleanliness etc.). Microbiological contamination of process equipment, machines and systems such as ventilation and air-conditioning equipment causes growth of pathogenic bacteria. The amount of air supplied and removed from a room depends on its use and load of odours and hazardous material. As a result of dew point formation in ventilation systems may appear the so-called air-borne condensation nuclei on which steam settles when the air gets oversaturated. The air flow rate has a material influence upon comfortable conditions in human inhabited zones. In manufacturing shops where the highest air quality is a priority, radial disinfection by means of catalytic ionization is applied. In food industry manufacturing shops of higher microbiological standard, ventilation systems based on air re-circulation should not be used.