Commonly available practical methods of plants ventilation are:
* Exhaust fans or Power Roof Ventilators (PRVs).
  To do a satisfactory job of eliminating excessively hot air, it is usually essential to have powered wall and/or roof exhausters. These fans should also help to control air pressure within the building whether it be negative or positive pressure.
* Supply Fans or PRVs.
  A large number of buildings use exhaust PRVs to exhaust fumes, smoke, dust or other contaminants unavoidable in the operation of the business. As a result, these buildings are frequently under a severe negative pressure. The solution to the problem of this kind is usually found in the use of supply fans or "make-up" air ventilators.