A Technology That Changed the Map
The machinery of air conditioning, a compressor, coils and fans, is not very different from that of a refrigerator. What made it significant was where it could be used. Once a building’s air could be cooled and dried on demand, the climate of a place mattered less to where people could comfortably live, work and gather. This article follows those consequences; the engineering is covered elsewhere.
Before Cooled Air
Buildings in hot regions had long been designed to manage heat without machines. Thick walls, high ceilings, shaded porches, courtyards, shutters and cross-ventilation all helped. In the United States, hot-weather life in many places was organized around the sun: people slept on porches, shops closed in the afternoon, and legislatures sometimes adjourned for the hottest months. Cities in hot climates tended to grow slowly compared with those in temperate ones.
Industry and Public Buildings First
The earliest large-scale users were manufacturers who needed stable humidity and temperature. The textile industry used controlled humidity to keep thread from breaking, and printers needed paper that would not swell. Air conditioning then moved into places where crowds gathered. Movie theaters adopted it in the 1920s, and for the first time summer became a good season for attendance rather than a poor one. Department stores, hotels and restaurants followed, since cool rooms were an advertised attraction.
Government buildings also adopted it. The chambers of the U.S. House and Senate were cooled in the late 1920s, and offices later became places that could be used productively through a long summer.
Changing the Shape of Buildings
Air conditioning changed architecture in several ways:
- Deeper floor plans. Buildings no longer had to be narrow so that every desk was near a window for light and air.
- Sealed facades. Large glass curtain-wall towers, which would be unbearable without mechanical cooling, became common in the mid-20th century.
- Lower ceilings and less ornament for ventilation. Tall transoms, operable windows and airshafts became less essential.
- Mechanical rooms. Ducts, chillers and cooling towers became a standard part of the design of any large building.
Critics have pointed out that many of these buildings depend on energy use to remain habitable, and that older passive-cooling knowledge was sometimes lost along the way. Architects today often try to combine the two.
Regional Growth
The effects on regional development are widely discussed, though economists and historians weigh them differently. In the United States, the growth of the South and Southwest after World War II is often linked to the spread of air conditioning, alongside other factors such as highways, defense spending, cheap land, new industries and migration for jobs. Cities such as Houston, Phoenix and Atlanta grew rapidly during these decades. It would be too simple to say that cooling alone explains that growth, but it made year-round work, shopping and school more tolerable, and so removed one reason to avoid hot regions.
Similar patterns appear elsewhere. In parts of East and Southeast Asia and the Gulf, dense, fast-growing cities have relied on cooled offices, shopping malls and apartment blocks. Some political leaders have described cooling as important to economic development, though that is an argument rather than a settled finding.
Homes and Daily Life
In houses, the shift was gradual. Window units arrived first, followed by central systems in new suburban homes. As more homes were sealed against the heat, porches lost their role as the main summer living space, and people spent more evenings indoors. Some observers link this to changes in neighborhood life, though the evidence is mixed because other forces, such as television, were also drawing people inside.
Costs and Trade-offs
Cooling at scale brought new problems:
- It uses a lot of electricity, with peak demand often driven by hot afternoons.
- Outdoor units release heat into streets, which can add to urban heat in dense areas.
- Some early refrigerants damaged the ozone layer, as discussed in the account of refrigerant gases.
- Access is unequal: people without cooling are more vulnerable in heat waves, and rising demand is a concern as temperatures climb.
Efforts to ease these costs include more efficient equipment, better insulation, and pairing cooling with renewables such as solar panels. Data centers also depend on large-scale cooling, so even cloud computing is tied to this technology.
A Quiet Revolution
Unlike the telephone or the automobile, air conditioning rarely gets the credit it deserves for social change, partly because it works invisibly. Its history shows how a household-scale technology, applied to buildings and cities, can quietly shift where people settle and how they build.