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Cold Comfort

Sharon rigs up a DIY air conditioner to cool her apartment without warming the planet.

Friday Aug 24, 2007.     By Sharon Hoyer

Lifestyle Feed

When I was eight years old, my dad gave me a rough explanation of the utility meters behind our house. I was enthralled; it was the first time I realized the lamps, radios and television I took for granted were interconnected, the end points of an elaborate system running through the walls. Watching the wheel in the electric meter turn was like watching the brain of our house cogitate. I ran from room to room, flipping on every light and dashing back outside to see how fast I could make the wheel spin.

This formative moment came back to me the day my roommate brought home an air conditioner. I'm a conservationist of both the natural world and my own meager income, so the Danby Designer window unit looked, to me, like an electro-monetary black hole in our living room. I came home one sweltering night to find my roommates enjoying a frigid living room; I had visions of ComEd employees gleefully hugging each other as they watched our meter whirl with the same child-like enthusiasm I experienced some 20 years prior. As my sweaty skin took on a delicious chill, though, I had to concede that, in mid-August, a device capable of dropping the temperature in a room by 20 degrees feels like nothing short of a miracle. But there had to be a way to make our apartment tolerable without consuming an additional 1,200 watts per hour. So I did a little research.

An air conditioner works by pumping fluid through two sets of metal coils. As the fluid travels through one set, it evaporates into a gas and cools the coils. A fan blows hot air from the room over the cold coils, which absorb heat. The gas then travels into a compressor to be converted back into liquid, becoming extremely hot in the process. The hot liquid travels through the second set of coils, outfitted with another fan to blow hot air out the back of the unit. The cooled liquid then travels back to the evaporative cold coils and continues the cycle. Not exactly an easy process to replicate, right?

Necessity being the immortal mother of invention, it was a broke college student who devised a homemade air cooling system and posted the specs online. His version uses cold water for the heat transfer and eliminates the compressor/condenser half of the cycle. The simple-to-construct device operates on the power of a floor or table fan, between 50 and 150 watts per hour—about one-tenth the electrical output required to run a window unit AC. The promise of saving that much energy was all the motivation I needed to build one.

The parts: You'll need one floor or table fan, about three feet of rubber tubing, two large water-tight containers, twine or wire and several feet of flexible copper tubing. The copper tubing performs the heat transfer so the more you use, the more efficient the system. I bought it at the local hardware store for $1.20 per foot. I found nine feet was about the right amount for a standard oscillating fan; the larger the fan, the more tubing you'll need.

The specs: Bend the copper to cover the back of the fan in one large coil, starting at the center and working your way out, fastening it to the grill with twine or wire as you go. Cut the rubber tubing into two lengths and fit them snugly over each end of the coil. Fill one container with ice water and place into it the tube leading to the higher end of the coil. The cold water siphons through the tubing and drains into the second container, chilling the copper and absorbing heat from the air circulated by the fan. If you have an aquarium pump, you can create a continuous circuit by attaching it to the intake tube and placing the drain end in the same container. This method uses only an additional five to 10 watts per hour, and you don't need to keep rotating containers. Or suck through a rubber hose to get things started.

The homemade AC took no more than half an hour to construct. It looked about as sophisticated as a papier-mâché, baking powder-filled volcano and half as attractive, but, then again, the window unit isn't winning any beauty contests either. Over a hundred years of advancement in refrigeration technology and it still looks like an interior designer with a bad sense of humor stuck a microwave in your windowsill. Nonetheless, what matters on a 97-degree day is efficiency; the homemade unit cooled our 12-by-15-foot living room to a comfortable temperature in about a 30 minutes, consuming no more power than the fan I've been running all summer. As I watched the steady stream of water and felt the breeze from the fan grow colder, I marveled once again at the ingenuity of humankind.

It took a move from the regimented lawnscapes of the suburbs to the congestion of a major metropolis for Sharon to look twice at what she puts in the trash, down the sink and into her own body. She reports fortnightly on her endeavors to change "greening" from calculated deviation to a practicable way of life. You can contact her here.