Ventilation
refers to the movement and change of air in a building. Good ventilation is
necessary for human comfort and healthful indoor air. The quality of air in a
building should not contain contaminants which may be unpleasant or harmful.
Indoor air may be contaminated by unvented combustion in a building, the
building and finishing material and human activities. Ventilation air is used
to expel carbon dioxide produced by breathing and replace as well as dilute
odors and other indoor contaminants.
Air
consists of gases essential to life. It is a composition of nitrogen (78%),
oxygen (21%), carbon dioxide, other gases and water vapor. “Natural” air is
found outdoors in environments undisturbed by people. This air contains soil,
pollens, micro-organisms as well as plant and animal by products. It can also
contain minerals, ash, and gases from natural processes. The natural air is
ideal for human and other life forms. Air quality is important because the air
we breathe has a direct influence on us. In putting up impenetrable walls,
roofs and floors we trap and exclude some of these elements. Pollutants may
also be trapped in the internal living environment.
Natural air
is generally used as a source of ventilation. Air moves naturally through a
building when it is driven by temperature and pressure differences. Cross
ventilation is the horizontal movement of air through a building. Slight air
pressure builds up against one side of a building because of breezes blowing
against it. There is a pressure drop on the other side because of airflow
around the building. Air will be drawn through any openings on the side of the
building where there is pressure build up and attempt to escape through the
opposite side.
Inadequate
ventilation can lead to suffocation or poisoning of body cells from polluted
air. There may be an inadequate supply of oxygen to the brain for it to
function. People could suffer dizzy spells, migraines or respiratory failures
as a result. Poor ventilation can cause discomfort from smells. Inadequate
ventilation systems recycle stale and used air. Scents are sometimes used in
ventilation systems and may cause allergic reactions in some people. Other
types of allergens are biological allergens that may be airborne. Examples of
biological allergens are pollens, fungi, dust and animal dander. Fungi grow in
damp conditions. Allergens can be harmful to people with allergic conditions.
Bacteria
and viruses can be carried through the air and inhaled by people. Air
temperature and humidity have an effect on the time that bacteria and viruses
can survive outside the human body. Some disease is spread when
bacteria/viruses circulate through the air and are inhaled by others.
HVAC
systems are an important factor in the management of indoor air quality as we
continue building barriers between ourselves and the outdoors.