History
Circulating air
over or through water soaked materials is the basic concept behind evaporative air coolers. Centuries ago, in the Middle East ,
buildings were designed with wind shafts. These were located on the roof, catching
the wind, which would then pass through a reservoir of water. The wind, cooled
by water, was then directed into the house to cool the interior.
This concept
continued to be used, taking on many forms. In the 1920s, screened porches were
commonly used as sleeping porches, particularly in the southwest desert of the United States
Mechanized
The concept of air
cooled by water became mechanized in the 20th century, and the evaporative
cooler, as it was termed, became the subject of numerous patents. Elements used
in these coolers included wood wool pads, a reservoir with a float pump to
maintain levels, a pump and a powerful fan.
The fan draws in
the warm air from the outside. The air is pulled through the pads, which are
typically made of cedar shavings or plant cellulose. The pads are wet; the
water pump continually drenches them with water. The water from the pads
evaporates into the trapped air, which in turn lowers the temperature of the
air. It is then blown into the interior of the building through the ductwork.
Effectiveness
Evaporative air cooler
(desert cooler or swamp cooler) work best if the interior of the building is
not well sealed. Because the cooled air is being blown into the home, a window
or door left slightly open creates a pressure front, resulting in a more
forcible circulation of the cooled air. The "faster" the air moves,
the cooler if feels against the skin. Evaporative air coolers are more effective in regions with high temperatures but low levels of
humidity, such as the Middle East and the southwestern United States
Green Alternative
Air conditioners
use refrigerants such as chlorofluorocarbons and hydro-chlorofluorocarbons to
cool the air that is then blown into the interiors of buildings. These
refrigerants are considered by some to be harmful to the ozone layer.
Evaporative air coolers use no refrigerants. The basic components are air, water, and pads made
from wood or cellulose. The only chemicals used are those used in the
manufacture of the pads; they are impregnated with a chemical compound to
protect them against rot.
The cost of
operating an evaporative air cooler can be up to two-thirds less than operating an
air conditioner.The basic
operative principle, though, prevents this device from being the dominant
cooling system in the United States and Europe . It is dependent on low humidity levels for
effectiveness.
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