During the last three decades ventilation philosophy has been experiencing major
changes. In the first decade of this period, considerable efforts were made towards
understanding the mechanisms of air infiltration in buildings in order to control and
often reduce the fortuitous ventilation and conserve energy. In some cases, the reduction
in air infiltration created problems associated with the air quality in buildings and
the generic term ‘sick building syndrome’ came into being. The second decade of the
same period experienced concerted efforts to understand the causes of sick buildings,
which resulted in the introduction of new ventilation concepts, such as the age of air,
and new air quality units, and a consensus for increased outdoor air flow rates. In
the third decade, the emphasis on reducing energy consumption and environmental
consciousness has focused the minds of researchers and designers alike on the potential
of natural ventilation and user control of the local environment. As a result of
these changes, new ventilation standards and guidelines have been written to reflect
the importance of ventilation on the quality of indoor environment.