Continental Design & Engineering Newsletter

Great Inventions of the 20th Century

1902 Air Conditioning

It's a sweltering, muggy day in Central Indiana. You step outside and feel like you've been dealt a physical blow by the intense heat. Luckily, though, it's only a few short steps to your air-conditioned car, and then a few more steps from the car to your air-conditioned office. But have you ever considered what life would be like if air conditioning had never been invented?

The story behind air conditioning actually begins, believe it or not, thousands of years ago in Persia. Wind shafts were placed strategically on rooftops, which would catch the wind, pass it through cold water, and blow it into the building.

The first person to discover that certain gases could be used to chill air was a 19th century British inventor, Michael Faraday, although his ideas along that line were mostly theoretical. It wasn't until 1902 that a mechanical engineer by the name of Willis Haviland Carrier invented an electrical system to control temperature and humidity for manufacturing. Residential sales of air conditioners, however, didn't really take off until the 1950's.

How does an air conditioner work?

Modern air conditioners use a heat pump to pump heat from a lower temperature heat source to a higher temperature heat sink, thereby causing heat to flow in the opposite direction. Most air conditioners use an electric motor to drive a compressor that causes pressure changes between two compartments and pumps a refrigerant around. The refrigerant is pumped into the cooled compartment, where the low pressure and temperature make the refrigerant evaporate into a vapor, taking the heat with it. In the other compartment, the vapor is compressed and forced through a heat exchange coil, condensing into a liquid as it goes. This rejects the heat previously absorbed from the cooled compartment.

The first air conditioners used gases like ammonia and methyl chloride. These gases were toxic and often resulted in fatalities when they leaked. In 1928 an engineer named Thomas Midgley, Jr. created the first chlorofluorocarbon gas (CFC), popularly known as Freon. This gas was much safer for humans and very stable, but as we know today, reaches the upper atmosphere when it escapes and is harmful to the ozone layer. Newer and more environmentally safe compounds for air conditioners have been developed in recent years and all CFCs are slated to be replaced with these by 2020.

Air conditioning puts a large strain on America's electrical power grid, especially during the warmest summer months. According to a 1995 study, the average air conditioner wastes 40% of its input energy; lost, somewhat ironically, in the form of heat, which has to be pumped out. Reducing the use of air conditioners and refining the current systems to make them more energy efficient is something that is desperately needed.

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