Air Conditioning Makes It Hotter


July 02, 1991|By ROBERT BURRUSS

KENSINGTON. — Kensington -- When I was young and wanted to be a writer of short stories -- which was right after I wanted to be an actor and movie director -- I wrote a story about a small town that was situated in a valley surrounded by high mountains.

In my story, the surrounding mountains would sometimes trap the air so that the summer temperatures would get uncomfortably high. But that had historically been one of the unique features of the town, and people accepted it. The high humidity on the trapped-air days was also a historical phenomenon -- probably the product of extra respiration of the trees in the town and on the lower slopes of the mountains.

The town's little airport, where the official temperatures were monitored, began to see record temperatures during the 1960s, when the airport began to receive commercial jets. By the early 1970s, the runway was lengthened for the bigger aircraft; and because of the bigger planes and additional travelers, the terminal building had to be expanded and supplied with powerful air conditioners to handle the summer heat plus the heat from the big jet engines.

The town's electricity was supplied by a power plant that was sited outside of the valley. In earlier years, the electric-power demand on hot summer days had been low, just enough to drive the electric refrigerators. But the power company's business grew considerably beginning in the late 1950s when the power demand for air conditioners began rising. By the late 1970s, when central air conditioning had stopped being a luxury and had become both a practical and an economic necessity -- a house without central air was worth less than one with it -- summer power demand reached record levels.

During an unusual summer in the mid 1980s, a stationary air mass hung over the town for a whole week. For eight days, the jet planes came and went, depositing and taking travelers, but always leaving the waste heat of the powerful engines. At the same time, the power plant outside the valley kept pumping energy into it as people turned their air conditioners to higher and higher levels because of the increasing heat. At midnight of the eighth day, the outside air temperature was 100 degrees, and people began arriving at the hospital. High temperature and high humidity were taking a fatal toll.

At this point, the hero of the story realized that the high outdoor temperature was from the electric energy that was driving motors of all the air conditioners -- in effect, the power plant outside the town was heating the air in the town. As the air got hotter, more people turned their air conditioners higher, which meant that more heat was being pumped into the town's trapped air mass, making things hotter and hotter.

Does such a scenario sound preposterous? Consider that on a hot Washington day in July or August Pepco pumps more than 5 billion watts of power into the metropolitan area. Over 8 hours, the total energy comes to nearly the equivalent of three Hiroshima bombs.

If you add to that the waste heat from the power-generation process, plus the heat from cars and buses and airplanes, the total thermal burden on the Washington Metro area these days is tens of times what it was in the 1930s and 1940s. The 5 billion watts for 8 hours corresponds to 14 BTU of energy per square foot of metro area -- enough to raise the temperature of the lower 100 feet of air by 7 degrees.

But hot air rises, you say. No, not with only a 7-degree difference over that of the surrounding countryside. In World War II we learned that the fuel content of whole cities was necessary to power a city-sized convection column. Short of burning the city, hot air just clings to the ground.

Go stand by the heat exchanger of your central air conditioner. You will be warmly surprised by the thermal output of your house. Try to imagine how much heat comes from the terminal buildings at BWI, Dulles and National Airport where the temperatures are setting records.

The number of houses with air conditioners increased fivefold between 1960 and 1979. Also, those colorful weather maps on television and in the newspapers -- those large areas of regional high record temperatures are based on point data taken mostly at airports that have been growing over the same period -- i.e., bigger terminal buildings, more powerful air conditioners, plus the heat of large jet engines.

Global heating and greenhouse theory don't have to be invoked to explain the record temperatures of the 1980s. the waste heat of increased summer energy usage is a plausible source of the record temperature. Quite possibly the more we use air conditioners, the more we need to use air conditioners.

D8 Robert Burruss is an engineer and free-lance writer.

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