The need for ventilation usually results from the necessity to control the concentration of contaminants that may produce objectionable odours or toxic effects. It is also used to improve occupational environments and to discharge heat, moisture and contaminants arising from industrial processes. Ventilation needs depend on the occupancy and building use. It is, therefore, an important consideration in building design. The Ventilation Process Ventilation may involve one or both of two processes.
Good design is required to achieve an effective arrangement.
This approach is widely used in industrial applications, an exhaust hood often utilized over cooking ranges being a common example. Where an entire room is a source of contamination, an exhaust system may be used to isolate it from the rest of the building, as is often done with washrooms. In most situations the sources of contaminants, usually the occupants themselves and their activities, are not readily isolated. The ventilation process then employed is that of dilution. Fresh air is thoroughly mixed with the air in the occupied space and displaces an equal volume of room air, which is at the average room condition when it leaves the space.