Too often it falls upon ventilation to accomplish tasks for which it is not appropriate. The prime role of ventilation is to dilute and remove pollutants from unavoidable sources. In essence these are those generated by occupants themselves and by their essential activities. All other pollutants should be controlled by elimination or source containment. Some pollutants are chemically reactive, adsorbed on to surfaces, or have emission characteristics which are stimulated by the ventilation process itself.

The quantity of ventilation needed depends on the amount and nature of pollutant present in a space. In practice an enclosed space will contain many different pollutants.

Ventilation energy demand can be reduced considerably by adopting a variety of energy efficient ventilation techniques. These include:

Minimising the need for ventilation: Energy demand may be curtailed by ensuring that the need for ventilation is reduced. This means minimising emissions from avoidable pollutant sources. Any extra ventilation needed to dilute and remove avoidable pollutants can be equated directly against conditioning load.

Poor ventilation can be associated with unhealthy buildings. Miller (1992), for example, highlights the association of increasing bacteriological concentration with decreasing ventilation rates, while Billington (1982) has produced an historical review of the role of ventilation in improving health and reducing the spread of illness. Studies reported by Sundell (1994) and others have shown that symptoms of building sickness can occur at all ventilation ranges.

Ventilation needs and strategies differ according to occupancy patterns and building type. Main considerations are: