Innovative solutions for creating healthy, efficient, eco-friendly homes

Foundations: Technology Beats the Heat

Keeping a home warm was relatively simple once we had fire. But making a home cool in hot weather was a problem that took millennia of human history to solve. Even the usually clever Romans were technologically helpless against sweltering Italian summers: They resorted to sacrificing dogs in hopes the gods would lift the heat that accompanied the rising of Sirius, the Dog Star, every July. Mechanical air conditioning that cooled and dehumidified air didn't germinate until the early 19th century, after scientists noticed that evaporating liquids absorb heat (the reason rubbing alcohol feels cold on your skin). Engineers harnessed that phenomenon with a deceptively simple vapor-compression machine: A gas, called the coolant, is run through a compressor to condense it into a liquid. Then the high-pressure liquid is released through an expansion valve into pipes under lower pressure, where it expands back into a gas. The expanding liquid absorbs heat from the air or water surrounding the pipes, creating a cool area. In 1851, a doctor named John Gorrie received the first U.S. patent for a mechanical refrigeration machine. Gorrie - who lived, appropriately, in Florida - was convinced that cool air helped cure patients with yellow fever. So he designed a vapor-compression machine that used compressed air and water as a coolant to make ice for patients' sick rooms. Unfortunately, Gorrie was unable to raise money to mass-produce his machine and died, poor and distraught, in 1855. A few decades later, in July 1881, naval engineers built a crude air conditioner to ease the suffering of President James Garfield, dying of a gunshot wound in the oppressive Washington, D.C., heat. The contraption, made from ice-water-soaked sheets and ventilator fans, lowered the room's temperature by 20°, but it consumed a quarter-million pounds of ice in two months. Clearly, a mechanical cooling system like Gorrie's was needed. Fortunately, engineers had refined vapor-compression refrigerators, developing systems for breweries, meatpacking facilities and other industrial uses. Most used coolants, such as sulfur dioxide, ether and ammonia, and took advantage of newly commercialized electricity to power compressors and fans. But these systems still didn't address humidity control - a breakthrough provided by Willis Carrier. In 1902, while working for a furnace company, Carrier set out to help a Brooklyn printer struggling to print clear images in hot, humid weather. Carrier's solution was a set of cooling refrigerator coils and a mist-spraying feature that controlled the level of moisture in the air. He patented his "apparatus for treating air" in 1906. The term "air conditioning" came that same year from Stuart Cramer, a textile engineer who patented another device that added moisture to the air in textile mills. By 1915, Carrier had formed his own company, selling air conditioners to office buildings, theaters and department stores - the only places big enough to accommodate the enormous machinery. "The difference between these first systems and modern air conditioners is like the early room-sized computers compared to today's desktop PCs," says Jon Shaw, Carrier's senior manager of corporate communications and self-appointed company historian. To make residential air conditioning feasible, Carrier developed smaller motors and compressors. But he needed a new coolant, since substances such as ammonia were troublingly toxic and flammable. In 1929, scientists working for DuPont and General Motors delivered chlorofluorocarbons - non-toxic, nonflammable, extremely efficient coolants that could be produced cheaply and in prodigious quantities. Of course, scientists realized later that chlorofluorocarbons murdered the earth's ozone layer, a nasty side effect of the subsequent boom in home air conditioning. Almost immediately, Carrier and Philco began selling single-room home air conditioners, but they had to halt production during World War II. Not surprisingly, home air conditioning took off in the 1950s, as developers like William Levitt began putting central AC in their suburban houses. In 1960, 12.4 percent of U.S. households had some kind of air conditioning, according to the U.S. Census. By 1997, that number had grown to 72 percent nationwide and 93 percent in the South, where air conditioning has played a significant role in the region's dramatic population growth. Air conditioning's 50-year reign doesn't appear to be slipping, even though many environmentally conscious or frugal homeowners are turning to the nearly forgotten art of natural home cooling with well-placed shade trees, awnings and interior curtains. Manufacturers have responded, too, with improvements, such as high-efficiency compressors and heat-transfer coils, and safer replacements for chlorofluorocarbons. But 150 years later, the vapor-compression system used by John Gorrie to cool hospital rooms remains the backbone of today's air conditioners and an immutable component of modern life.