History of Evaporative Cooling Technology
1.2.1 Discovery of
Evaporative Cooling
All of us experienced the evaporative cooling
effect that occurs after exiting a swimming pool on a hot sunny day. It
probably did not take long past the initial discovery of cloth for early man to
take practical advantage of this physical cooling behavior of water when living
in hot and arid regions.
Frescoes or plaster paintings from about 2500
B.C. show slaves fanning jars of water to cool rooms for royalty. The earliest
archeological trail of buildings incorporating mechanisms for evaporative space
cooling starts in Ancient Egypt with paths spreading quickly to other regions
having hot and dry climates. These mechanisms include the use of porous water
pots, water ponds, pools, and thin water chutes integrated in various ways into
thick walled and shaded enclosures to yield areas that would have been cool and
provided an escape from the heat of the day. While it is clear that our
ancestors took advantage of evaporative cooling, it wasn't until more recent
times that the physics of evaporation and the hydrological cycle were clearly
understood so that components and features could be effectively engineered to
yield improved and repeatable performance results.
1.2.2 Uncovering the physics behind Evaporative
Cooling
The history of some key scientific discoveries
and developments in the science of psychometrics is as follows:-
Ø First Hygrometer:
Leonardo da Vinci at the beginning of the 16th century was
credited with inventing the first hygrometer that used a ball of wool to
provide this indication of humidity level.
Ø First Mechanical Air Cooler:
Da Vinci was likely the first to use a mechanical air cooler. This
air cooler consisted of a hollow water wheel with an air passage constructed to
guide the air from the water wheel to his patron's wife's boudoir. The air was
cooled by the splashing and evaporation of water during operation of the water
wheel. Motive power was provided to move the air by the water turning a
partially submerged wheel. Namely, as sections of the wheel would be submerged
into the stream water level moved from the outer edge of wheel toward the
center compressing the air in this chamber and forcing it to move through the
passages to the boudoir.
Ø Psychrometric Charts:
Willis Carrier's development of a psychrometric chart similar to
ones in use today along with the development of a formula that linked the
transformation of sensible heat into latent heat during the adiabatic (no
external heat input or output) saturation of air. This development is being
done in 20thcentury.
1.2.3 Early Evaporative Cooling in the Southwest
Settlers of the 1920s and 1930s in the Southwest slept in screened
in porches, roofs, or other outside facilities and hung wet sheets to gain some
relief from the summer heat. The Arizona Republic reports that guests at the
Ford Hotel in Phoenix slept on the balcony while young men peddled to power
overhead fans. There were cases of pneumonia during the summer as some wrapped
themselves in wet sheets and slept in front of an electric fan.
The 1986 edition of Dr. John Watt's Evaporative
Air Conditioning Handbook identifies the origins for modern American
evaporative cooling as either from the East Coast or Southwest. In the early
1900s, air washers were invented in the East and air coolers were developed in
Southwest (Arizona and California). The air washers passed air through water
spray, which cleaned and cooled the air in textile mills and factories in New
England and the Southern coastline. The Southwestern air coolers included
indirect coolers, where air passed over a water-cooled coil, and direct coolers
where air was cooled by direct contact with water.
The earliest design of the direct coolers
consisted of wooden frames covered with wet burlap cloth with fans forcing air
into the space being cooled. As they evolved, sumps and recalculating pumps
were incorporated into the designs. After a few evaporation passes, scale would
form on the pads. To mitigate this, some of the water would be discharged or
bled to a drain.
Eventually, the design for direct coolers
(called wet-boxes, desert coolers, drip coolers, and then swamp coolers)
evolved to the common configuration of two-inch excelsior (wood chip or aspen)
pads sandwiched between chicken wire and nailed to the cooler frame.
The first aspen pad (swamp) cooler was
demonstrated in the Adams Hotel in downtown Phoenix June 20, 1916. In 1939,
Martin and Paul Thornburg published mimeographed instructions, "Cooling
for the Arizona Home." The two professors at the University of Arizona had
conducted tests to improve performance of these direct evaporative coolers.
About that time, early mass production of
evaporative coolers began as the integrated motor and fan units manufactured by
Emerson Electric Company became available. Among the very first of these mass
produced coolers were from Goettle Brothers Inc. By 1939, most houses and
businesses in the hot and arid southwest were using drip coolers. By the early
1950s, a large number of manufactures had joined the market and were producing
coolers for a market that covered much of the USA, Canada, and offshore to
countries such as Australia.
This is all about history of Evaporative Cooling Technology.
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