Ventilation systems are required for industrial and commercial buildings where the there are a large no. of occupants, or where heat generating machines are operating and the heat is to be removed. Natural ventilation is not usually satisfactory for such cases. Moreover 'Forced Ventilation' helps maintain a positive pressure inside a zone thereby preventing dust ingress.

Fan ventilation is necessary to maintain conditions at a satisfactory standard. Three different systems may be adopted :

i. Supplying of fresh air. The air may be filtered by means of pre/fine filters.
ii. Extraction of stale air.
iii. A combination of above, also known as 'Push-Pull' system.

The 3rd system is most effective. The fresh air from atmosphere can be routed through GI duct work and supplied on different zones based on requirement. Similarly part of supplied air can be removed so as to maintain positive pressure inside the zone.