5 Cool Ways Air Conditioning Changed the World

In many places, it is nearly impossible to imagine surviving the summer months without the relief of air conditioning. Not only do air conditioning systems bring down indoor temperatures, but they can also reduce humidity, providing a stark contrast to the hot, muggy outdoors. 

Air conditioning is not as universal as running water or electricity, and in many parts of the world it is mostly found in offices, hospitals, and commercial buildings. In Mexico, only 16 percent of households had air conditioning in 2018 according to the International Energy Agency; in India, the number was 5 percent. In the United States, however, 89 percent of households were air conditioned in 2020, and states as varied as Florida, Iowa, and New Jersey had air conditioning rates of 96 percent or greater. Nationally, they are more common in households than clothes washers, gas stoves, or second televisions. 

But here are five air conditioning facts you may not know or haven’t thought about.
 

How it started

Before the 20th century, buildings could be kept cool through ventilation or blocks of ice. Mechanical icemakers that operated via vapor-compression refrigeration—the process by which an expanded working fluid draws heat from its surroundings and cools it to potentially very low temperatures—were developed as early as the 1850s, but the first air conditioning system was installed at the Sackett-Wilhelms Lithographing & Publishing Company in Brooklyn in 1902. (It was the humidity control offered by air conditioning that was important to the printing operation.)

Willis Haviland Carrier, who installed that first system, went on to found the Carrier Air Conditioning Company, in 1915, and Carrier became a household name in climate control. 
 

Office buildings

Initially, the size and expense of air conditioning systems limited their installation to factories and office buildings. In 1928, the first high-rise office building built with air conditioning in mind was opened in San Antonio, Tex. The 28-story Milam Building used chilled water piped to fans that circulated the cool air through every floor. 

The Milam Building was made of brick and reinforced concrete, but starting in the 1950s, a new architectural style developed that required large air conditioning systems. Tall office buildings clad entirely in glass let in so much sunlight that their interiors would quickly become unbearably hot, even in the middle of winter. Because these floor-to-ceiling windows cannot be opened, air conditioning is essential to their habitability. 

For its first of a kind system, the Milam Building was named an ASME Engineering Landmark.
 

Sunbelt surge

By the middle of the 20th century, office buildings, department stores, and movie theaters adopted air conditioning (and became places to go to beat the heat). It would take longer for homes to join the air conditioning trend. Rather than cool the entire house, the first air conditioners for home use were sized for a specific room, such as a bedroom or living room, and designed to sit on a window ledge. H.H. Schultz and J.Q. Sherman developed the first unit of that type in 1931, but their invention was too costly for wide adoption. After World War II, engineer Henry Galson designed a less expensive window air conditioner for Fedders and that led to greater adoption. The fraction of households with air conditioning in the U.S. surged from around 10 percent in the late 1950s to more than half by the early 1970s and has increased steadily since. 

The availability of household air conditioning had a marked effect of population growth in the U.S. In many parts of the American South, the hot, muggy summers deterred people from relocating from the Northeast or Midwest. Widespread air conditioning made those summers more bearable, and as a consequence states like Florida and Texas saw their population double or even triple between 1960 and 2000. 
 

Ozone layer

In the mid-to-late 20th century, the most common working fluids in air conditioners, refrigerators, and other cooling machines were a type of chemical known as chlorofluorocarbons (CFCs). While these chemicals were efficient for absorbing heat in refrigeration cycles, when leaked they were found to have a serious impact on ozone in the upper atmosphere. That thin film of ozone formed a protective barrier against ultraviolet rays, and its depletion was implicated in an increased number of reported cases of skin cancer.

After nations of the world agreed in 1987 to phase out CFCs, manufacturers began to replace that refrigerant with a new class of chemicals called hydrofluorocarbons (HFCs) that do not eat away at the ozone later. Unfortunately, HFCs are potent greenhouse gases that trap infrared light between 700 and 1,500 times more effectively than carbon dioxide over a 100-year period. (For their part, some CFCs were 10,000 times more powerful greenhouse gases than CO₂.) Now, companies are working on air conditioning and refrigeration systems that use propane, isobutane, or even CO₂ as the working fluid. 
 

Improved gas mileage?

It took some effort to miniaturize air conditioning units to fit in an automobile, but the luxury car brand Packard became the first automobile manufacturer to offer an air conditioning unit in its cars in 1939. Today, air conditioning is standard in most cars.

Because automobile air conditioners operate off power from the engine or battery, running an AC can have a significant impact of fuel usage. When idling or at speeds associated with city driving, it is more fuel efficient to drive with the windows down and use cross ventilation for cooling. But scientists at Oak Ridge National Laboratory conducted experiments published in 2013 that showed at highway speeds, a sedan like a Toyota Corolla used more fuels when travelling with the windows down, due to the penalty due to increased drag, compared to the cost of running the AC. For an SUV, the drag penalty was never greater than the energy required to run the AC, but at highway speeds the difference was negligible. 

Of course, most Americans no longer think about fuel economy when considering turning on the AC in their cars. From house to road to store or office, they live in a constantly air-conditioned world. 

Jeffrey Winters is editor in chief of Mechanical Engineering magazine.