Sweltering summer heat seems to sap the energy of everyone, and in some cases it can be fatal. Air conditioning, which relies on some simple principles, provides relief on even the most blistering summer day. Exploring the history and mechanics of this much-desired amenity of modern life is fun and educational.
History
In 1903, Willis Haviland Carrier put into operation the world's first mechanical temperature and humidity control machine--which is now called an air conditioner. That first air conditioner was meant to minimize the effects of humidity and temperature in a printing plant in Brooklyn, New York, so that the paper used would not stretch and make the ink used misalign. By 1906, Carrier had been granted a patent for an "apparatus for treating air." What is important about Carrier's invention was not that it cooled and regulated the humidity of a space, but that it was the first successful mechanical method of doing so.
Function
The function of air conditioning has remained essentially the same since Carrier's day--to reduce humidity and lower the temperature of a living or working space. Over the years, air conditioners have become increasingly efficient and have also included filtration elements that remove dust and other particulate matter from the air.
But air conditioning is not only useful for keeping people comfortable in modern buildings. It's used to control the humidity and temperature in libraries and archives so that the fragile paper lasts longer, and even in the Pyramids, where the perspiration and moist exhalations of thousands of tourists every year threaten to erode and destroy 5,000-year-old murals.
Principles
Air conditioning works on the most basic of principles: evaporation. Evaporation is the method the human body uses to keep its temperature regulated. If the body gets too warm, water in the form of "sweat" is excreted through small ducts in the skin. The warmer surroundings cause the sweat to become a vapor (evaporation), and in doing so uses some of the heat from the body. This results in a cooling effect. A similar principle is used in air conditioners, with the exception that instead of using water, the machine uses a liquefied gas called chlorodiflourocarbons (CFCs). Many know it by the trademarked name "Freon." When the CFC is compressed, it becomes very cold and liquefies. It is then run through a coil of tubing behind which a fan is blowing, passing warmer air over the cool coils. The CFC inside warms up, transferring the cool to the air, making it feel cold. The CFC then goes back into a compressor to return it to liquid form, and the process begins all over again.
Types
There are two main types of mechanical air conditioners that use CFCs as their cooling component: central units and window units. Central units tend to be installed at one fixed point and use a series of ducts and thermostats to control the temperature inside. Window-mounted units are more portable, can be removed during colder weather, and are mainly used to cool small areas such as a single room.
Expert Insight
In modern building design (since the 20th century), there has been increasing accommodations made for mechanical air conditioning--for example, increased loads for electricity and ducts for central air conditioning. This has led to relatively inefficient building designs that tend to absorb a lot of heat from the sun and thus require increased use of air conditioning. Since the energy crisis of the 1970s, there has been an increased concentration on the use of other technologies and methods to help maintain a cooler building so as to reduce the use of air conditioning. Among these are insulation, more moderate use of air conditioning during peak times, and the return to ventilation of outside air.
