Air conditioning

If you were fortunate enough to be able to spend last week in a climate-controlled environment, give thanks to Willis Haviland Carrier, whose new-fangled invention, air conditioning, first went into service 100 years ago, on July 17, 1902.

Modern air conditioning is an offshoot of an earlier invention, mechanical refrigeration, which is based on the fact that liquids absorb heat from their surroundings when they evaporate or boil. By controlling the liquid’s pressure, you can control the temperature at which this happens: the lower the pressure, the lower the boiling point.

In both refrigerators and air conditioners, a compressor compresses a gas, which heats up as it is pressurized. Coils (on the back side of a refrigerator, or in the part of an air conditioner that’s outside the building) let this hot gas dissipate enough heat that it condenses into a pressurized liquid. The hot high-pressure liquid flows through an expansion valve, which reduces its pressure so that it instantly boils and vaporizes. This process uses up the heat the gas is carrying, so that it becomes icy cold. This cold gas then flows through a set of coils which cool the inside of the refrigerator or, in an air conditioner, a flow of air. The gas is then sucked up by the compressor, and the cycle repeats.

William Cullen of the University of Glasgow demonstrated refrigeration using this principle in 1748, but it was 86 years before Jacob Perkins patented the first practical ice-making machine in London.

Modern air conditioning had to wait for Carrier, who, in 1902, was just one year out of Cornell University and employed by Buffalo Forge Co. One of his company’s clients, the Sackett-Wilhelms Lithographic and Publishing Co. in Brooklyn, was having trouble with its printing press: the paper was expanding and contracting in the heat and humidity, and as a result, the printers couldn’t align the ink properly.

Carrier came up with a simple solution. The printing plant was heated in the winter by blowing air over hot coils full of steam; so, he reasoned, why not cool it by blowing air over coils full of cold water (cooled by mechanical refrigeration). As an added bonus, the water vapor in the air would condense on the cold coils, dehumidifying the air as well as cooling it.

Carrier’s system did the trick, but air conditioning was slow to move beyond industrial plants. Movie theatres in the 1920s were the first public places to take advantage of air conditioning; next were the department stores. Congress was air-conditioned in 1928 (allowing politicians to make mischief all year long, grumbled Gore Vidal) and the White House in 1929. Planes started being air conditioned in the mid-1930s, and the first air-conditioned car, a Packard, went on the market in 1939.

It wasn’t until the 1950s that air conditioning really took off, though. In 1955, developer William Levitt made air-conditioning standard in the new homes he built north of Philadelphia. By 1960, 12 percent of the U.S.’s homes were air-conditioned; today, 80 percent are (96 percent in the south).

Until recently, the most common refrigerant was Freon or one of its variants. Introduced in 1930, these chlorofluorocarbons (CFCs) were implicated half a century later in the depletion of the Earth’s ozone layer; ironically, they were developed because of the need for something safe to replace other hazardous refrigerants of the day, such as sulfur dioxide. (The earliest refrigeration systems used safe but relatively inefficient air or water.) Stable, incombustible and non-toxic, it was Freon that made air conditioning practical in office buildings, hospitals, apartments, trains, planes, buses and automobiles.

However, under The Montreal Protocol on Substances that Deplete the Ozone Layer, an international treaty signed in 1987 and modified several times since then, CFCs are being phased out in favor of hydrochlorofluorocarbons (HCFCs) which are much less damaging to the ozone layer, and hydrofluorocarbons (HFCs) which don’t damage it at all. More than 120 countries are signatories of the treaty.

Today, a hundred years after Willis Carrier’s brainstorm, you can hardly find a large building, or mode of transportation that isn’t cooled to perfection (and sometimes beyond) no matter how hot the temperature is outside.

Which just leaves one question: how come, in any room containing two people, especially if they are husband and wife, is one is always too hot and the other too cold?

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