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Invention & Technology MagazineSpring 2005    Volume 20, Issue 4
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TEXAS ARCHITECTS HAVE MORE REASON THAN THEIR neighbors to remember the Alamo: This old missionturned-fortress was designed to provide coolness. Like many other buildings in the region, it has thick adobe walls. These served as insulation, keeping heat out of the building during the day and, once warmed, helping make the interior comfortable during the chill of night.

Other cooling methods are older still. The ancient Greeks, Romans, Jews, and Chinese all collected ice and snow for cooling. An eighth-century caliph, Mahdi of Baghdad, supposedly kept hundreds of slaves busy going back and forth to the mountains for snow that cooled his summer residence when it was poured between specially built double walls. Other, less labor-intensive approaches have included towers and domes to draw off hot air from below and pools or cisterns to cool rooms by evaporation. While many of these measures were ingenious, none of them worked very well. They helped make dwellings habitable, but genuine comfort was another matter. For most of human history, cold has been a greater luxury than heat.

Not until well into the Industrial Revolution did the means arise to cool a room by using machinery. The first American to try it was John Gorrie. He was a doctor in charge of the U.S. Marine Hospital in Apalachicola, Florida, where yellow fever was common. Following a severe outbreak in 1842, he sought new ways to treat it. He knew that it arrived with the heat of summer and vanished with the milder weather of autumn, and he concluded that the way to fight yellow fever was to keep patients in a cool room. Using ice, he eventually succeeded in chilling a hospital ward.

The ice had been imported from New England, whose merchants were then enjoying a brisk trade in natural ice, cutting blocks from frozen lakes and shipping them as far as India with sawdust for insulation. But Apalachicola was just a small town on the Gulf Coast, and supplies of natural ice were unreliable, so Gorrie turned his attention to inventing a machine that would make it. Not surprisingly, Apalachicola lacked a technical library, but in New York City he found the publications he needed.

Gorrie learned that as early as 1755 the Scottish physician William Cullen had artificially generated temperatures low enough to make ice. Cullen did this by using an air pump to create a partial vacuum. Water within the evacuated chamber boiled violently, driving off much of its internal heat (in today’s terms, the most energetic molecules in the water became vapor). The liquid water’s temperature fell sharply, eventually causing it to freeze. Other British scientists improved and extended this idea in the early nineteenth century.

American researchers were also active. As early as 1805 Oliver Evans, one of the new nation’s first mechanical engineers, published a description of a refrigeration system that included a compressor, a condenser, and a cooling coil. He died in 1819 without ever building it, but in 1834 his friend Jacob Perkins went further. Working with diethyl ether, a volatile fluid obtained from India rubber, Perkins followed Evans’s lead and built what amounted to a prototype of a modern mechanical refrigerator. It compressed gaseous ether until it was liquefied, used water to absorb heat from the warm liquid, and then reduced the pressure and let the ether evaporate, which made it very cold. The machine produced a small amount of ice, which was enough to win Perkins a patent.

John Gorrie’s apparatus generally followed that of Perkins, though without the liquid-gas phase transition. It used a pump to compress air, which made the air hot. Gorrie removed the heat with cold water and then allowed the air to expand. The expansion made it cold enough to produce ice. In effect, Gorrie cooled the air by increasing its temperature.

Gorrie’s process took advantage of the difference between temperature and heat. You can compress a gas without adding heat, but you will be raising its temperature by bottling up its molecules in a smaller space. Similarly, if you let a gas expand, its temperature will drop, even if you have not removed any heat. So if you compress a gas, draw off part of its heat, and then let it expand, it will be colder than it was to begin with. This is the basic idea behind refrigeration.

Unfortunately, the technology of Gorrie’s time was insufficiently advanced to produce the tons of ice per day that would have been needed to cool the hospital. He made enough ice to chill bottles of champagne for a party but could not get the financial support he needed to develop his idea commercially.

At the same time, engineers in other nations were experimenting with treating and cooling air. When Great Britain’s House of Commons was rebuilt after an 1834 fire, David Boswell Reid designed a system that cleaned its air and could also heat or chill it and add or remove moisture. The cooling could be accomplished by mixing nighttime and daytime air, by exposing hot air to a spray of cold water (as Willis Carrier would do more systematically decades later), or by passing the air over ice. In the late 185Os James Harrison of Australia installed ether-based cooling equipment in a pair of breweries, one in England and one in Australia. This was the world’s first large-scale industrial use of refrigeration.

But the path to real cooling called for the use of ammonia rather than air or ether as a refrigerant. Ammonia boils at a convenient -28 degrees Fahrenheit and has a substantial “latent heat,” meaning that it absorbs a large amount of heat when it vaporizes. If your refrigerator doesn’t merely compress a gas into a denser and hotter gas but converts it into a liquid, then each gas-liquid-gas cycle will transfer that much more heat. The use of latent heat represented another important principle in the new field of refrigeration.

Ferdinand Carré, of France, was the first to work with ammonia as a coolant, building his initial apparatus in 1860. Then, beginning in the mid-1870s, Carl von Linde of Munich, Germany, took the lead in creating improved ammonia refrigerating machines. He started by showing how the efficiency of such machines could be calculated using the emerging science of thermodynamics. Then he showed how that figure could be increased (at the time, most refrigerating equipment was less than 20 percent efficient). In 1877 he obtained a patent for an improved refrigerating machine, which was installed in a Trieste brewery the following year.


In America the cattle industry adopted refrigeration early. In the mid-1870s the King Ranch in Texas bought an ammonia refrigerating machine for its meat-processing operations. The same decade saw the introduction of refrigerated ships and railroad cars, both primarily at the instigation of the meat industry.

The King Ranch refrigeration machine was designed by David Boyle, a transplanted Texan then living in Chicago. Boyle, like so many entrepreneurs, had begun his business with a lemonade stand. In Demopolis, Alabama, in 1865, he bought a shipment of ice, “used it to cool lemonaid, and sold it at a good profit to the yankee soldiers”- thousands of dollars’ worth, he later recalled. This experience awakened him to the profits that could be made from refrigeration.

As refrigeration grew more common and more powerful, engineers began to contemplate treating the air of large rooms. As early as 1891 Eastman Kodak used refrigerating equipment to reduce the humidity of air in its plants, making it easier to dry out film and emulsion. In this case, the point of the process was not to cool air but to dry it; cooling was just an effective way of doing so, because cold air cannot hold as much moisture as warm air (that’s why water condenses on a cold surface). That same year a St. Louis restaurant and beer hall optimistically named the Ice Palace installed refrigerating equipment and brought the room temperature below 75 degrees when the temperature outside was close to 90.

For companies too small to afford their own equipment, entrepreneurs in several cities built central plants and sold cooling as a utility to which businesses in specified areas could be connected for a fee. All these services were short-lived. The first successful one was the Colorado Automatic Refrigerating Company, which opened in Denver in August 1889. Subscribers were not given cold air directly; instead, they got liquefied ammonia, which was pumped through one-inch cast-iron mains beneath Denver’s streets. At the user’s building, the ammonia flowed from a pinhole outlet into a network of coils in the space being chilled. There it expanded into gas, cooling the surrounding air, before being sucked back to the company’s plant through a return main. At the plant the gaseous ammonia was dissolved in water for temporary storage, then extracted and liquefied to start the process anew.

The system could maintain temperatures as low as 25 degrees Fahrenheit, and since the ammonia in liquid form was at or near ambient temperatures, it absorbed no heat in transmission. Similar companies were established in other cities, including St. Louis and Atlantic City. Most of them seem to have gone under in the 1890s and early 1900s, probably not only for economic reasons but also because of the problems associated with using ammonia as a coolant. Other district cooling systems over the years have used cold water or brine as a coolant instead of ammonia. As late as the 1930s systems of this sort were built in the areas around Rockefeller Center and the U.S. Capitol, and in recent years the idea has undergone a revival in scattered places.

The next big step came from a consulting engineer named Alfred Wolff, who in 1892 designed a ventilation system for Carnegie Hall, in Manhattan. Using racks of ice to cool the air, it worked moderately well, though the hall, like most theaters, still had to close during the height of the summer. But Wolff’s experience with this system and others like it persuaded him that controlling both temperature and humidity was crucial, because air that was too dry or too clammy could be just as uncomfortable as air that was too hot.

In 1902 Wolff took a step toward addressing this issue while solving a different problem, the installation of a winter heating system in Andrew Carnegie’s house. The Carnegie system used a steam pipe to humidify the dry air of the season, and to regulate this process, Wolff introduced adjustable humidity control. The most important feature was the use of two thermometers, a standard one and a “wet-bulb” type, which was wrapped in a damp cloth from which water continuously evaporated. The dry-bulb thermometer was part of a thermostat, and the wet-bulb thermometer, which gave a reading a few degrees lower, was equivalent to a humidity reading: The greater the humidity, the lower the temperature gap. Carnegie’s servants could set the gap to any desired level. The system could not remove moisture from the air, only add it, but in winter the main problem was dry air, not excess humidity.

During that same year, Wolff built a cooling and drying system for the boardroom of the New York Stock Exchange. The NYSE system dehumidified air by simply blowing it past coils filled with ammonia-cooled water and letting the excess humidity condense on the coils and drip out. This was not a precise arrangement, and it didn’t help that Wolff lacked exact data on the properties of humid air. He therefore set his equipment to run at a single set of conditions, with no instruments to measure humidity or adjust the system. But even this roughand-ready arrangement was good enough to operate successfully for 20 years. Wolff went on to install systems at the Metropolitan Museum of Art and many other buildings, and he would probably have played an even bigger role in the development of air conditioning had he not died in 1909 at the age of 50.

In 1902, as Wolff was designing his Carnegie and NYSE installations, a young engineer named Willis Carrier, widely regarded as the founder of modern air conditioning, began his long career in the field of cooling and moisture control. He had recently graduated from Cornell University and was working at the Buffalo Forge Company, a maker of ventilation equipment in Buffalo, New York, when his boss gave him an assignment. A printing firm in Brooklyn was having trouble printing in color. The paper was absorbing moisture from the air and swelling, which kept the successive impressions in different colors from properly aligning with one another.

Carrier installed a system that used the same principle as Wolff’s, blowing air over cold coils and letting the moisture drip out. He refined the technology by using two sets of cooling coils. One carried cold water from an artesian well; the second achieved greater cooling by chilling its water with an ammonia refrigerating machine. The goal was a maximum 55 percent humidity at temperatures of 70 degrees in winter and 80 degrees in summer. The system worked poorly because the coils allowed a great deal of moisture-bearing air to pass through the gaps between them. Another problem was that the treated air had to be distributed through previously installed heating apparatus instead of purpose-built equipment, so it did not disperse properly. Still, the possibilities of air treatment excited Carrier, though he knew there had to be a better and more systematic way of controlling humidity.

His first real contribution to the field began to take shape later that year as he waited for a train in Pittsburgh. It was evening; the temperature was in the low thirties, and the depot was wrapped in a dense fog. Carrier thought about the chilling mist and realized that creating something like it in his ventilating systems could hold the key to controlling and adjusting humidity. “Here is air approximately 100 percent saturated with moisture,” he later wrote. “The temperature is low so, even though saturated, there is not much actual moisture. There could not be at so low a temperature.”

That was his crucial insight. Because the ability of air to hold moisture decreases with decreasing temperature, even if cold air is saturated with moisture, it will still have a low relative humidity when it is heated up. “Now, if I can saturate air and control its temperature at saturation,” he continued, “I can get air with any amount of moisture I want in it. I can do it, too, by drawing the air through a fine spray of water to create actual fog.” The trick was to chill the water first and then spray it into a chamber. With a huge number of tiny droplets, a cold mist would cool and dehumidify the air much more efficiently than any set of coils and would yield a reproducible result.

In the spirit of John Gorrie, who cooled air by heating it, Carrier would dry air by moistening it. And if he wanted to increase the air’s humidity rather than decrease it, he could use a warm mist instead. By controlling the temperature of the mist, he could achieve any desired humidity. In practice, after the air was treated with mist, it was blown through a chamber with baffles, which separated the water droplets from the saturated air. As a bonus, the mist also helped cleanse the air of dust.

The new technology needed a name, and the man who provided it was Stuart Cramer. A North Carolinian who worked in the textile industry, he knew very well that dry factory air could make fibers break. One way to avoid this was by exposing the fibers to moist air in storage rooms, a process called “yarn conditioning.” Cramer decided to attack the problem at the other end and announced in 1906 that he had installed humidifiers of his own invention in his plant’s weaving rooms. He called the innovation “air conditioning.” Initially the name meant only the control of humidity, but it soon embraced temperature as well.

Meanwhile, Carrier was broadening his conquests. Working mostly on humidity control, he applied his findings in a lengthening list of industrial settings. He had so much business that in 1907 his bosses in Buffalo established a subsidiary called Carrier Air Conditioning Company of America. By 1911 Carrier’s clients included paper, pharmaceutical, film, tobacco, candy, and bakery companies. Carrier successfully addressed such problems as gelatin pills that took too long to dry, chocolate that turned gray, and movie film that developed spots.


Despite his success, all these installations were based on educated guesswork. Carrier was the top man in his field, but he had no way to calculate how a given space would respond to a given set of equipment, and thus no sure way to achieve a specified combination of humidity and temperature. His experience had given him a very good feel for air-conditioning needs, but it was hard to pass that expertise along to anyone else or apply it to unfamiliar conditions.

The study of moist air is called psychrometrics (the prefix psychro means “cold”), and a century ago its fundamentals were in poor shape. The standard set of formulas dated from 1886 and amounted to a mere summary of experimental data, with no basic principles behind them. Constants within those formulas had also been determined by experiment and contained their own errors. But Carrier saw that the means were at hand to place psychrometrics on a solid analytical footing.

He began with the physical principles that governed the behavior of moist air, expressing these principles as mathematical equations and using them to derive additional formulas. Most important was an equation that expressed the moisture content of damp air in terms of pressure and wet-bulb and dry-bulb temperatures. Depicted graphically in the form of charts, these formulas made it possible to predict the performance of an air-conditioning unit with some precision. Carrier presented this work in a 1911 paper, “Rational Psychrometric Formulae.” It established air conditioning as a new engineering discipline.

Carrier now not only could control humidity; he could do so with the accuracy of a thermostat controlling temperature. By mixing chilled air with untreated air that was allowed to bypass the cooling spray, he could achieve any desired combination of humidity and temperature. This made him think about selling his invention to a wider audience by persuading businesses to use air conditioning for comfort rather than for industrial needs.

A manufacturer could easily justify the cost of air conditioning by the increased production it made possible. The decision was much harder for a restaurant owner because there was little evidence that cool air would attract enough new customers. After all, air conditioning was expensive. There was the cost of installation, plus an engineer to run it, plus power costs (which were not cheap) and frequent maintenance. Moreover, the refrigeration equipment of the day still ran on ammonia, which was noxious and toxic and capable of forming explosive mixtures. Such costs and risks were accepted in an industrial setting, but most owners of service businesses did not want to deal with them.

Around the time of World War I, the advent of elaborate motion-picture palaces changed the outlook. In Chicago the brothers Barney and Abe Balaban and Sam and Maurice Katz, working together, took the lead with their ornate Central Park and Riviera Theaters. An engineer named Frederick Wittenmeier built air-conditioning systems for these theaters that used carbon dioxide as the coolant (a method that had been pioneered in 1866 by Thaddeus Lowe, better known as a Civil War balloonist). This gas demanded high-pressure equipment, which tended to leak. But it was odorless and became toxic only in very high concentrations, not to mention being nonexplosive and nonflammable.

“Removes the Temper from Temperature,” read a 1919 newspaper ad for the Central Park Theater, which also promised “refreshingly cool air, as invigorating as the balmy mountain breezes.” The Carrier Engineering Company, now an independent firm, got into the act soon afterward by working with Sid Grauman, of Los Angeles, who had already built that city’s Chinese and Million Dollar Theaters. Grauman’s third theater, the Metropolitan, opened early in 1923 and included air conditioning among its attractions.

One question that took a while to decide was how to distribute the cooled air. Early systems blew it through vents in the floor because that worked best with heated air. But since cold air tends to sink, it did not mix readily with the warmer air above it, and customers’ feet froze. Thus the pioneering Central Park and Riviera systems yielded poor results, and engineers soon learned to replace floor vents with ceiling ones.

Carrier’s earlier units had used reciprocating compressors, which basically moved back and forth like the pistons on a locomotive. In 1922 he switched to a centrifugal model, which compressed the coolant with a rapidly spinning rotor. The centrifugal pump greatly reduced the size of his machinery and made it easier both to install and to use.


Carrier also sought nontoxic and nonflammable refrigerants that could improve on carbon dioxide. His initial choice was dielene (dichloroethylene, or C2H2Cl2), which required lower pressures and hence was easier to use. It was readily available commercially since it was also used as a cleaning agent. When Carrier set out to air-condition New York City’s Rivoli Theater, the city safety commissioner denied the necessary permit. Carrier went to the man’s office, poured some dielene into a container, and put a match to it. It burned as calmly as a candle. The safety chief granted the permit.

The Rivoli was the first New York theater to offer air conditioning and also the first major public test of Carrier’s dielene and centrifugal compressor. The system made its debut on Memorial Day in 1925. Moviegoers brought fans along in case it didn’t work. Adolph Zukor, the head of Paramount Pictures, was on hand for the opening, and as Carrier recalled, the air conditioning was slow getting started: “The people poured in, filled all the seats, and stood seven deep in the back of the theater. We had more than we had bargained for and were plenty worried. From the wings we watched in dismay as two thousand fans fluttered.”

Then, Carrier continued, “gradually, almost imperceptibly, the fans dropped into laps as the effects of the air conditioning system became evident. Only a few chronic fanners persisted, but soon they, too, ceased fanning. We had stopped them ‘cold.’” After the film Zukor told Carrier, “The people are going to like it.”

While his centrifugal compressor was a success, Carrier knew that dielene was not the end of his search for the ideal refrigerant. He experimented with trichloroethylene, C2HCl3, and then méthylène chloride, CH2Cl2, which had still better properties. He liked it so much that he adopted it as a standard coolant. Claiming that it gave “twice the refrigeration without increasing the machine size,” he named it after himself: Carrene-1.

Then in 1930 the DuPont chemist Thomas Midgley introduced the first of his chlorofluorocarbon refrigerants, known as Fréons. Carrier visited his lab and learned about a gas that was produced in an intermediate step. Midgley had no interest in it, but Carrier saw that for his purposes it might be even better than methylene chloride. It was Freon-11, CCl3F, which he adopted and named Carrene-2. It lacked the high latent heat of ammonia, but it worked well at modest pressures. This made it easier to compress and helped avoid leaks.

With improved refrigerants and machinery, the way seemed open to selling air conditioners for use in the home. “Palm Beach Air Daily,” advertised the firm of Doherty-Brehm in 1931, boasting that it now offered “the first effective, reasonably priced air conditioning system for dwellings.” However, the price was “as low as $875.” That was enough to buy two Chevrolets. Even worse, perhaps, Doherty-Brehm’s system required machinery substantially larger than an oil-burning furnace to be installed in the basement.

A more promising approach lay in self-contained window units, the first of which arrived in 1932 from the De La Vergne Engine Company. This model dispensed with the water-spray air washer that everyone had been using for the past quartercentury and returned to the days of Alfred Wolff, when moisture dripped from the cooling coils and customers had to accept whatever humidity corresponded to the air’s new temperature. In return, purchasers got a compact, easily adjusted installation that cost less and needed no plumbing connection and no mechanic to install.

De La Vergne’s air conditioner was a hit within the industry, as dozens of firms lined up to license the patent rights and build their own versions. It made far less of a hit with the public. The smallest portable one-room cooler cost $400, and in the midst of the Depression, people preferred to fan themselves and drink iced tea while they waited for prices to drop. A 1938 survey showed that of 22 million American homes with electricity, only 55,000 had air conditioning (though more than 90 percent of movie theaters did).

Sales to homeowners might lie out of reach, but Carrier believed he could sell air conditioners to owners of office buildings. As with his industrial units, he could pitch them as a spur to production, since employees would do more work if they felt more comfortable. The first high-rise office building to have central air conditioning was the 21-story Milam Building, in San Antonio, Texas, which opened in January 1928.

San Antonio was a particularly brutal testing ground for Carrier. The radiant heat from the Texas sun was intense, and few nearby structures were anywhere near the Milam Building’s size. Yet with a large cooling plant in the basement and smaller units every two floors, the system he designed could handle eight tons of air per minute, providing a total change every seven to eight minutes—roughly in line with today’s standards. It is a tribute to his abilities that some of the original equipment remained in use until 1990.

Unfortunately, there was a problem with central-station systems in office buildings: They required voluminous ductwork. The ducts had to be large, even when insulated, to keep the conditioned air from warming en route to offices that might be hundreds of feet away (the smaller the pipe, the more air is close to its surface). This ductwork took up space that might have been used for offices, and architects and building owners didn’t like that. The Empire State Building, which opened in 1931, might have made a spectacular showcase for air conditioning, but for this reason, it had none.

Carrier responded by separating the operations of dehumidification and temperature control. His new central unit generated an abundant flow of dehumidified air, which ran at high speed through narrow conduits. Each office had its own console, which heated or cooled this air by passing it over coils carrying hot or cold water. The system was centralized, but it enabled individual workers in separate offices to adjust the temperature to their taste.

Carrier filed for a patent on this refinement in August 1939 and began making sales. Early buyers included the Statler in Washington, D.C., the last hotel in the nation to be built before Pearl Harbor. After the war the Secretariat Building of the United Nations became another important customer. Built in the International Style that had been created by the architect Le Corbusier—tall, slablike, all-glass buildings—it had windows that could not be opened. That became a nearly universal feature of air-conditioned offices.

Air conditioning had gone to war after 1941, with refrigerants being declared strategic materials while cooling for comfort was put on hold. But postwar prosperity encouraged a number of firms to try anew with window models for home use. Companies such as Frigidaire and Fedders had been manufacturing kitchen refrigerators, which gave them useful experience. Sears, Roebuck took to selling air conditioners as well.

Dropping prices and improving quality led to increasing sales. In 1946 the industry sold 30,000 room air conditioners. By 1950 sales had risen to 193,000, and in 1956 they reached 1.3 million. The 1960s saw a boom, with the number of units in service rising from 6.5 million in 1960 to 24 million in 1970. More than 7 million of these were central units that cooled the entire house. They were put in during construction, and many of them restored the air washer along with precise humidity control. At century’s end the tally was 57.3 million central systems and 23.5 million homes with room units, in a total housing stock of 107 million.

As often happens in technology, what had been a luxury soon became a necessity, and levels of performance once considered unimaginable became routine. In the 1920s, 80 degrees in summer and 70 in winter was a reasonable standard. Nowadays buildings are cooled so fiercely that many workers wear sweaters year-round.

Air conditioning for cars developed in parallel, starting with autos that were designed for the rich and rapidly spreading to the masses. R. Buckminster Fuller included air conditioning in his prototype Dymaxion car in 1933. The 1938 Nash offered a “Weather Eye,” a fan-based ventilation system that did not cool the air but at least circulated it. The 1939 Packard was the first production car to feature air cooling, which added 25 percent to its price tag. The equipment filled up the entire trunk, and an on/off switch was the only adjustment. Cadillac followed in 1941 with a similar system in which the air conditioning was always on when the engine was running, unless the driver lifted the hood and removed a belt connected to the compressor. A postwar modification put the controls inside the car, but they were relegated to the back seat.

These installations were heavy and bulky, they leaked readily, and their controls were all but impossible to adjust while driving. Yet there was clearly a demand for them. After the war some Continental Oil stations in Texas installed curbside air conditioners that pumped cars full of cold air. If you were careful, your car might stay tolerably cool until you reached the next station.

In 1954 the Nash-Kelvinator Corporation, a division of American Motors, produced a compact and practical automotive airconditioning unit, as did the Harrison Radiator Division of General Motors. Still, by 1963 only 14 percent of the cars sold in the United States had factory air conditioning, and nearly all of them were sold in the South and Southwest. But as production grew, manufacturers introduced units that were lighter in weight, cost less, and were more reliable. Just as 1920s drivers suddenly realized that they didn’t have to freeze or get drenched in open cars, 1960s drivers suddenly realized that they didn’t have to bake on hot days. The air-conditioned share of the auto market topped 50 percent in 1969, and by 2000 some 98.4 percent of new cars provided this benefit.


What did air conditioning do for America? Porch culture in rural areas, and stoop and street culture in the cities, declined as Americans chose to stay indoors and watch television instead. Business productivity improved as bosses no longer sent employees home on hot days; a 1957 survey showed that 88 percent of a large sample of companies rated air conditioning as the most important source of “office efficiency.” Led in large part by the demand for air conditioning, installed capacity for generating electricity has risen from 102 million kilowatts in 1953 to 480 million in 1975 to more than 900 million today.

In recent decades, states in the Sunbelt have grown enormously while Northern ones have grown feebly or even lost population. This flood of Northern transplants has, for good and ill, made the South more like the rest of the country. Arizona, New Mexico, and Nevada, which had been barren deserts, welcomed the arrival of suburban sprawl, and California came to dominate the nation and the world in a number of fields.

Not everyone liked air conditioning. One major complaint was that people in air-conditioned houses kept their windows closed. “Every place is air-conditioned,” the playwright Horton Foote complained in 1995. “I don’t hear the train whistles like I used to. That haunting lonely sound. When the cotton mills were running full-time and they had a cotton-seed mill, we would have this wonderful odor permeating the house. I find myself thinking, ‘What was that really like and why did it vanish?’”

The story of air conditioning is not as dramatic as many stories in the history of technology. It contains no outsize personalities, startling demonstrations, or sudden shifts, and even Willis Carrier’s eureka moment hardly ranks with Newton and the apple. The general pattern with air conditioning has been for widespread adoption to lag behind invention by at least a couple of decades. Yet the effects of air conditioning have been just as momentous as those of, say, anesthesia or the transcontinental railroad. Instead of a single great breakthrough or a monumental achievement, it was more a matter of individual consumers purchasing room units at Sears. In this quiet fashion, a hundred million appliance buyers transformed the nation.

T. A. HEPPENHEIMER lives in Fountain Valley, California, where he says air conditioning is rarely needed.

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