The battle of the air conditioner

By TOMER SPINNER
August 6, 2009 12:03
3 minute read.

 
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She sat frozen and miserable under the wall-mounted air conditioner. Then the slender graphic designer gathered her courage and bravely turned it off - to the cheers of the other girls in the office. Two seconds later a 100-kilo guy, red-hot with anger, leaped to turn it on. It seemed the infamous battle of the air conditioner was on again between Ms. Graphics and the heavyweight programmer. Luckily a fellow worker with some physics background suggested they tilt up the air blades (vanes) guiding the A/C outlets. Voila! Further R&D suggested raising the AC temperature to a sensible 24º-25º, buying a little fan for Mr. Hot and asking the lady to keep a light sweater handy. It turns out that saving energy can help save workplace relations. "Clearly, [vanes] of the popular wall-mounted ACs should be tilted down in winter, since warm air floats up. But a common mistake is to leave them in winter mode during summer," explains engineer Rafi Aharoni of Assa-Aharoni, a firm of green building, energy and cooling consultants. Cold air sinks, he explains, so in summer vanes should be kept horizontal to allow cold air to better circulate, increase the comfort level of a room and save energy. "Regular cleaning of AC air filters is important for both health and efficiency reasons. Another simple tip is not to throw away the old fan when buying an AC. Using a fan to assist the AC can achieve [an additional 1-3 temperature degrees] of comfort. When each degree decreases electricity consumption by some 5 percent, this amounts to a substantial saving." How important is insulation? "Economically, it's the best investment," says Aharoni. "I insulated my home's roof in Haifa with 10 centimeters of polyurethane foam, painted white. I open the windows for night ventilation and hardly have to use the AC on summer nights. My neighbors living in similar houses without improved insulation pay less attention to ventilation, shading or roof color... so they pay twice as much or more for air-conditioning. In office buildings improved insulation may return the investment even after a year, but unfortunately the minimal Israeli standard is not imposed. Modern office buildings today generally have poorer energetic performances than in the 1960s and '70s." If you find up-and-down moving AC vanes unnecessary, you're probably right. "These are probably a gimmick," says meteorological physicist Dr. Baruch Ziv of the Open University. "I've seen them jam in the wrong direction, up in winter or down in summer. What was wrong with simple manual adjustment of air outlets in the old floor-mounted ACs?" "Efficiency is the name of the game," stresses Aharoni. "Most old ACs are terribly inefficient and should be trashed and replaced by new ones using government subsidy. The current electricity crisis can be solved if the National Infrastructures Ministry starts giving serious incentives to companies installing highly efficient, advanced central cooling systems. "Hi-tech accountants were surprised to find their branches in Atidim Park [North Tel Aviv] pay about $2 a month electricity per square meter - twice as much as the branches [of the same companies] in Matam Park [Haifa]. It turned out that Matam's energy diversion systems [chilling water using low night electricity tariffs] and other innovations account for the $100,000-a-month difference between the two parks, which have the same total area." Getting a blow of hot air from an exterior AC unit (condenser) is one of summer's nastiest experiences. All along Rehov Ibn Gvirol in Tel Aviv, ACs are huffing and puffing this heat into the semi-enclosed corridor, creating a very unpleasant heat trap. Signs hung on the corridor walls further obstruct ventilation. "Exterior AC units should not be installed in semi-enclosed spaces. These heat traps are major AC-compressor killers," explains Aharoni. "We've measured 45º inside heat traps when ambient temperature was only 32º. The hotter it is outside, the harder the compressor works. "So heat traps shorten the life of air conditioners and inflate electricity bills. It's a vicious circle: Heat is not properly expelled, it warms the building again, ACs have to work harder and so on. Before installing a new AC in a restaurant, for example, check with a certified consultant if hot air can be expelled from the building using vents which consume negligible energy. In projects where it's necessary to conceal AC units, we often use vents to neutralize heat traps."

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