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Air Conditioning |
Overview
What is air conditioning?
Air conditioning is the removal of heat
from indoor air for thermal comfort. In
another sense, the term can refer to any
form of cooling, heating, ventilation,
or disinfection that modifies the
condition of air. An air conditioner
(often referred to as AC or air con.) is
an appliance, system, or machine
designed to stabilise the air
temperature and humidity within an area
(used for cooling as well as heating
depending on the air properties at a
given time), typically using a
refrigeration cycle but sometimes using
evaporation, commonly for comfort
cooling in buildings and motor vehicles.
The concept of air conditioning is known
to have been applied in Ancient Rome,
where aqueduct water was circulated
through the walls of certain houses to
cool them. Similar techniques in
medieval Persia involved the use of
cisterns and wind towers to cool
buildings during the hot season. Modern
air conditioning emerged from advances
in chemistry during the 19th century,
and the first large-scale electrical air
conditioning was invented and used in
1902 by Willis Haviland Carrier.
A little history of air conditioning...
The 2nd century Chinese inventor Ding
Huane (fl. 180) of the Han Dynasty
invented a rotary fan for air
conditioning, with seven wheels 3 m (9.8
ft) in diameter and manually powered. In
747, Emperor Xuanzong (r. 712–762) of
the Tang Dynasty (618–907) had the Cool
Hall (Liang Tian) built in the imperial
palace, which the Tang Yulin describes
as having water-powered fan wheels for
air conditioning as well as rising jet
streams of water from fountains. During
the subsequent Song Dynasty (960–1279),
written sources mentioned the air
conditioning rotary fan as even more
widely used.
In the 17th century Cornelius Drebbel
demonstrated "turning Summer into
Winter" for James I of England by adding
salt to water.
In 1758, Benjamin Franklin and John
Hadley, a chemistry professor at
Cambridge University, conducted an
experiment to explore the principle of
evaporation as a means to rapidly cool
an object. Franklin and Hadley confirmed
that evaporation of highly volatile
liquids such as alcohol and ether could
be used to drive down the temperature of
an object past the freezing point of
water. They conducted their experiment
with the bulb of a mercury thermometer
as their object and with a bellows used
to "quicken" the evaporation; they
lowered the temperature of the
thermometer bulb down to 7°F while the
ambient temperature was 65°F. Franklin
noted that soon after they passed the
freezing point of water (32°F) a thin
film of ice formed on the surface of the
thermometer's bulb and that the ice mass
was about a quarter inch thick when they
stopped the experiment upon reaching
7°F. Franklin concluded, "From this
experiment, one may see the possibility
of freezing a man to death on a warm
summer's day".
In 1820, British scientist and inventor
Michael Faraday discovered that
compressing and liquefying ammonia could
chill air when the liquefied ammonia was
allowed to evaporate. In 1842, Florida
physician John Gorrie used compressor
technology to create ice, which he used
to cool air for his patients in his
hospital in Apalachicola, Florida.[7] He
hoped eventually to use his ice-making
machine to regulate the temperature of
buildings. He even envisioned
centralized air conditioning that could
cool entire cities.[8] Though his
prototype leaked and performed
irregularly, Gorrie was granted a patent
in 1851 for his ice-making machine. His
hopes for its success vanished soon
afterwards when his chief financial
backer died; Gorrie did not get the
money he needed to develop the machine.
According to his biographer, Vivian M.
Sherlock, he blamed the "Ice King",
Frederic Tudor, for his failure,
suspecting that Tudor had launched a
smear campaign against his invention.
Dr. Gorrie died impoverished in 1855 and
the idea of air conditioning faded away
for 50 years.
In 1902, the first modern electrical air
conditioning unit was invented by Willis
Haviland Carrier in Buffalo, New York.
After graduating from Cornell
University, Carrier, a native of Angola,
New York, found a job at the Buffalo
Forge Company. While there, Carrier
began experimentation with air
conditioning as a way to solve an
application problem for the
Sackett-Wilhelms Lithographing and
Publishing Company in Brooklyn, New
York, and the first "air conditioner,"
designed and built in Buffalo by
Carrier, began working on 17 July 1902.
Designed to improve manufacturing
process control in a printing plant,
Carrier's invention controlled not only
temperature but also humidity. Carrier
used his knowledge of the heating of
objects with steam and reversed the
process. Instead of sending air through
hot coils, he sent it through cold coils
(ones filled with cold water). The air
blowing over the cold coils cooled the
air, and one could thereby control the
amount of moisture the colder air could
hold. In turn, the humidity in the room
could be controlled. The low heat and
humidity were to help maintain
consistent paper dimensions and ink
alignment. Later, Carrier's technology
was applied to increase productivity in
the workplace, and The Carrier Air
Conditioning Company of America was
formed to meet rising demand. Over time,
air conditioning came to be used to
improve comfort in homes and automobiles
as well. Residential sales expanded
dramatically in the 1950s.
In 1906, Stuart W. Cramer of Charlotte,
North Carolina was exploring ways to add
moisture to the air in his textile mill.
Cramer coined the term "air
conditioning", using it in a patent
claim he filed that year as an analogue
to "water conditioning", then a
well-known process for making textiles
easier to process. He combined moisture
with ventilation to "condition" and
change the air in the factories,
controlling the humidity so necessary in
textile plants. Willis Carrier adopted
the term and incorporated it into the
name of his company. This evaporation of
water in air, to provide a cooling
effect, is now known as evaporative
cooling.
The first air conditioners and
refrigerators employed toxic or
flammable gases, such as ammonia, methyl
chloride, and propane, that could result
in fatal accidents when they leaked.
Thomas Midgley, Jr. created the first
chlorofluorocarbon gas, Freon, in 1928.
Freon is a trademark name owned by
DuPont for any Chlorofluorocarbon (CFC),
Hydrogenated CFC (HCFC), or
Hydrofluorocarbon (HFC) refrigerant, the
name of each including a number
indicating molecular composition (R-11,
R-12, R-22, R-134A). The blend most used
in direct-expansion home and building
comfort cooling is an HCFC known as
R-22. It is to be phased out for use in
new equipment by 2010 and completely
discontinued by 2020. R-12 was the most
common blend used in automobiles in the
US until 1994 when most changed to
R-134A. R-11 and R-12 are no longer
manufactured in the US for this type of
application, the only source for air
conditioning purchase being the cleaned
and purified gas recovered from other
air conditioner systems. Several
non-ozone depleting refrigerants have
been developed as alternatives,
including R-410A, invented by Honeywell
(formerly AlliedSignal) in Buffalo, and
sold under the Genetron (R) AZ-20 name.
It was first commercially used by
Carrier under the brand name Puron.
Innovation in air conditioning
technologies continues, with much recent
emphasis placed on energy efficiency,
and on improving indoor air quality.
Reducing climate change impact is an
important area of innovation, because in
addition to greenhouse gas emissions
associated with energy use, CFCs, HCFCs
and HFCs are, themselves, potent
greenhouse gases when leaked to the
atmosphere. For example, R-22 (also
known as HCFC-22) has a global warming
potential about 1,800 times higher than
CO2. As an alternative to conventional
refrigerants, natural alternatives like
CO2 (R-744) have been proposed.
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