It’s going to be a hot week for many Americans. If you’ve ever installed a window air-conditioning unit in your old apartment, you know that your AC is inexplicably heavy for the small space that it cools. The reason? It takes a lot of copper to produce all that cold air, Kelly explains. Her original piece, from 2011, is reprinted below.
With temperatures rising, Americans have begun the annual summer tradition of installing cumbersome removable air conditioners. It's tough to find a window unit that's lighter than 46 pounds—and a machine like that would be able to cool only a fairly small room (150 square feet or less). What makes them so heavy?
Copper, mostly. Air-conditioning systems—both centralized ones and window units—have three important components: an evaporator, a condenser, and a compressor. The evaporator helps cool the air, the condenser readies the refrigerant for the cooling process, and the compressor moves refrigerant back and forth between them. The evaporator and the condenser are both made out of copper coils, and there is some copper in the compressor, too. Copper is pretty heavy, weighing some 558 pounds per cubic foot, and the copper components account for as much as 60 percent of the weight in smaller units—though the percentage declines as they get heavier. (Units can be as massive as 213 pounds, the weight of the heaviest window unit sold by the Friedrich Air Conditioning Co.) Steel, which provides structural support and houses or covers the compressor, accounts for the rest of the weight.
Aluminum, which weighs about 169 pounds per cubic foot, could theoretically be substituted for copper. But manufacturers continue to use copper because it's a better conductor of heat. (That's important because an air conditioner works by essentially removing heat from the air.) Furthermore, the cost of an air-conditioning unit would increase if manufacturers used aluminum because of the new equipment and employee training they would have to invest in to make the necessary parts. Additionally, so much more aluminum would have to be used—to ensure that passageways in the unit were thick enough to withstand the high-pressure refrigerant moving through them—that units might not be that much lighter.
Mechanical engineers aren't particularly interested in making lighterunits. Instead, they're focusing on developing more ecological air-conditioning systems. One technique they're experimenting with is so-called "dew-point cooling," which relies on the natural energy produced by evaporating water, rather than fossil fuels. But it's not clear when greener units will be widely available—or if they'll be significantly lighter.
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Explainer thanks Jane Deming of Friedrich Air Conditioning, Ron Rajecki of HPAC Engineering, and Douglas T. Reindl of the Industrial Refrigeration Consortium at the University of Wisconsin-Madison.