Evaporative cooling is
becoming increasingly relevant as energy costs continue to skyrocket, because
it can be up to 80 percent more efficient than classic refrigeration or
absorption air conditioning. Evaporative cooling is simply cooling of air or
anything else by the evaporation of water or other liquids. It is easy to illustrate by merely pointing out
the effectiveness of perspiration cooling, the human body's own built-in
evaporative cooling system. Evaporative cooling works best in warm, dry
climates such as is found in the Southwestern United
States .
Latent Heat
Evaporative cooling in a coffee cup.Whether from a boiling pot or a wet towel,
water takes about the same amount of heat to vaporize, or turn from a liquid, a
lower energy state, into a gaseous form, a higher energy state. This is called
the latent heat of vaporization, and the heat source is any material or space
from which or in which the vaporization takes place.
Preferential Environments
Dry air has a particular affinity for moisture
because water has such a low partial pressure due to water, and it is
relatively easy for molecules of water that are moving rapidly to be absorbed
by the dry air and assumed in a gaseous form. This is why the visible spires of
water vapor rising off a hot cup of coffee disappear only several inches above
the cup. Therefore, evaporative cooling is far more effective in dry locales,
such as deserts and prairies, as opposed to tropical and subtropical climate
zones, such as Florida .
Perspiration
There is nothing quite like a brisk breeze on
a hot day, because more strident air movement presents perspiring skin with a
much higher volume of air with an affinity for water. Ceiling fans provide even
and steady air movement, which is often just enough to keep diners or sleepers
in tropical climes cool and comfortable. Dogs pant on a hot day because they
only perspire through their tongues, and the panting or rapid breathing
instinctively increases the amount of air passing over the tongue, which
absorbs the water that causes the evaporative cooling.
Nature's Cooling
Trees evaporate enormous amounts of water into
the air through their leaves, which is why many vacationers prefer a cool
stroll through a dense, tall forest on a hot sunny day to a walk on a beach.
Direct-Indirect Cooling
The only downside to evaporative air cooler is
that the air becomes more humid as it is cooled, which can be a trade off on a
hot, muggy day. For this reason, indirect systems evaporate water outside of
recirculating air ducting, so that a portion of the heat absorbed comes from
the living quarters, without the added humidity, which is subsequently
exhausted outside.
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