A history of air conditioning.

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July 15 2013 3:01 PM

A History of Air Conditioning

From ancient mountains of snow to the window units of today.

Many Americans are turning to their air conditioners to combat the current heat wave. These artificial breezes are a relatively novel innovation, however, as this history of air conditioning explains. Throughout the ages, humans have gone to great lengths to keep cool, from transporting mountains of snow to putting their underwear in the icebox, as Will Oremus reported in 2011. His original article is reprinted below.

Air conditioner. Click to expand image.
Staying cool in the summer is easier thanks to Willis Carrier
Will Oremus Will Oremus

Will Oremus is Slate's senior technology writer.

Anyone tempted to yearn for a simpler time must reckon with a few undeniable unpleasantries of life before modern technology: abscessed teeth, chamber pots, the bubonic plague—and a lack of air conditioning in late July. As temperatures rise into the triple digits across the eastern United States, it's worth remembering how we arrived at the climate-controlled summer environments we have today.

Until the 20th century, Americans dealt with the hot weather as many still do around the world: They sweated and fanned themselves. Primitive air-conditioning systems have existed since ancient times, but in most cases, these were so costly and inefficient as to preclude their use by any but the wealthiest people. In the United States, things began to change in the early 1900s, when the first electric fans appeared in homes. But cooling units have only spread beyond American borders in the last couple of decades, with the confluence of a rising global middle class and breakthroughs in energy-efficient technology.

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Attempts to control indoor temperatures began in ancient Rome, where wealthy citizens took advantage of the remarkable aqueduct system to circulate cool water through the walls of their homes. The emperor Elagabalus took things a step further in the third century, building a mountain of snow—imported from the mountains via donkey trains—in the garden next to his villa to keep cool during the summer. Marvelously inefficient, the effort presaged the spare-no-cost attitude behind our modern-day central air-conditioning systems. Even back then some scoffed at the concept of fighting heat with newfangled technologies. Seneca, the stoic philosopher, mocked the "skinny youths" who ate snow to keep cool rather than simply bearing the heat like a real Roman ought to.

Such luxuries disappeared during the Dark Ages, and large-scale air-conditioning efforts didn't resurface in the West until the 1800s, when well-funded American engineers began to tackle the problem. In the intervening centuries, fans were the coolant of choice. Hand fans were used in China as early as 3,000 years ago, and a second-century Chinese inventor has been credited with building the first room-sized rotary fan (it was powered by hand). Architecture also played a major role in pre-modern temperature control. In traditional Middle Eastern construction, windows faced away from the sun, and larger buildings featured "wind towers" designed to catch and circulate the prevailing breezes.

In late 19th-century America, engineers had the money and the ambition to pick up where the Romans had left off. In 1881, a dying President James Garfield got a respite from Washington, D.C.'s oppressive summer swelter thanks to an awkward device involving air blown through cotton sheets doused in ice water. Like Elagabalus before him, Garfield's comfort required enormous energy consumption; his caretakers reportedly went through half a million pounds of ice in two months.

The big breakthrough, of course, was electricity. Nikola Tesla's development of alternating current motors made possible the invention of oscillating fans  in the early 20th century. And in 1902, a 25-year-old engineer from New York named Willis Carrier invented the first modern air-conditioning system. The mechanical unit, which sent air through water-cooled coils, was not aimed at human comfort, however; it was designed to control humidity in the printing plant where he worked. In 1922, he followed up with the invention of the centrifugal chiller, which added a central compressor to reduce the unit's size. It was introduced to the public on Memorial Day weekend, 1925, when it debuted at the Rivoli Theater in Times Square. For years afterward, people piled into air-conditioned movie theaters on hot summer days, giving rise to the summer blockbuster.

It's not an exaggeration to say that Carrier's innovation shaped 20th-century America. In the 1930s, air conditioning spread to department stores, rail cars, and offices, sending workers' summer productivity soaring. Until then, central courtyards and wide-open windows had offered the only relief. Residential air conditioning was slower to take hold: As late as 1965, just 10 percent of U.S. homes had it, according to the Carrier Corporation. Families in the South made do by sleeping on the porch or even putting their underwear in the icebox. By 2007, however, the number was 86 percent. As cool air spread across the country, Sun Belt cities that had been unbearable in the summer became more attractive places to live and work, facilitating a long-term shift in U.S. population.

Europeans have been slower to embrace air conditioning, but like cold beer and ice water, it's beginning to catch on there, too. Data on air conditioning in the developing world is scarce, but it's safe to say most Africans and South Asians still make do without it. A recent Times of India article on how to stay cool in summer recommended wearing linens and drinking lots of fluids to avoid heat stroke. The modern Indian version of iced tea on the front porch? Nimbu paani from a street cart.