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The 60-Story Air Conditioner
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The 60-Story Air-Conditioner

by Douglas PageŠ1997

Know why the air is dirty? Mel Prueitt isn't finished.

A Los Alamos National Laboratory guest physicist in the Department of Wild Ideas named Mel Prueitt has designed a special structure that he's convinced can remove air pollution by actually bathing the air. Prueitt says about 100 units of his patented design, each the size of a 60-story skyscraper and each costing about $10 million, could clean half the air in a region the size of Los Angeles.

In Southern California, for instance, these structures - made of steel masts with fiberglass-coated Teflon stretched around the frames like 150-meter wide lamp shades - would be deployed around Los Angeles, Orange, Riverside and San Bernadino counties like rooks on a chessboard, taking in smoggy air at the top, washing it with pumped-in sea water, then blowing a breeze of clean, cool air out its fluted skirt so softly it would be difficult to fly a kite near the bottom.

The towers work on the principle of convection, which harnesses the phase-change energy associated with re-humidifying dry air.

What happens in a tower during the cosmic rinse cycle is this: Dry, dirty air is drawn into the towers and moistened by a sea-water mist spraying from a grid at the top. Thus damped and cooled, the air falls to the bottom and cleaning occurs on the way down as particles of pollution are attracted to the water droplets. At the bottom, the water is then treated to restore it to normal salinity, then returned to the ocean.

Free Electricity

All this air circulation creates enough wind to form a draft, which pulls even more dirty air in behind it, leading to another benefit: free electricity.

The wind in the tower turns turbines at ground level, which generate the energy needed to power the system's pumps, with several megawatts of surplus electricity left over. In practice the amount of surplus energy would vary, depending on weather conditions. The towers are more efficient in conditions of low-humidity; as the humidity drops the power output increases.

The idea of dumping polluted water into Santa Monica Bay is sure to turn the heads of local environmental groups, such as the Santa Monica Bay Restoration Project and the Surfrider Foundation. Some critics see this as just another scheme to sweep pollution under a different rug. David Hamilton, an architect with Verge Studios in Atlanta, incants the environmentalists' mantra: "This sounds like another technofix for a serious environmental problem. We cannot avoid the consequences of our actions by simply inventing a technology to make them go away. The answers are not 200 meter 'lamp shades', but conservation and new non-polluting technologies."

Other critics think an effort of this magnitude and expense would be more useful if it addressed prevention of air pollution rather than treating air soiled by bad habits. Electric automobiles are a favorite suggestion. Indeed, one could finance a fleet of 50,000 $20,000 electric cars for the $1 billion sticker price on 100 towers.

No Pollution Panacea

Prueitt does not promote his super structures as a panacea for pollution. He has merely taken the convection tower concept - which originated as a power-generation facility only - and moved it into the realm of urban smog clouds in order to clean some of the air while the power gets generated. "We'd be doing the same thing that nature does," said Prueitt. "All pollution sooner or later gets rained out of the air and ends up in the ocean. We short-circuit the process. We pick up pollution [in the towers] and put it in the ocean quicker, so people don't have to breathe it."

Most of the air around us could use the bath. A study last year by the Natural Resources Defense Council estimated there are 64,000 premature deaths annually from the effects of smog nationwide, 8,800 in Southern California alone - 170 people a week.

The idea of using convection towers to clean the air while generating power originated with scientist Phillip Carlson in the mid-Seventies. At Lockheed Corporation at the time, Carlson proposed building towers in the desert, driving the convection process with sea water to cool the air.

Carlson's concept has gained recent attention at Technion, the Israel Institute of Technology, where professor Dan Zaslavsky has shown the economic feasibility of convection towers. He wants to erect a single huge 'energy tower' over one-half mile high in the Israeli desert, drawing water from the nearby Red Sea.

Zaslavsky's tower, an airtight cylinder using sheet metal to cover a lattice shell 1,000 meters tall by 500 meters wide, would be capable of generating 500 megawatts of power at a cost of over $1 billion. Construction on a pilot plant is to begin this year.

Prueitt's towers are significantly smaller, but any one of the Bunyanesque shower curtains would surely dominate the mood of any neighborhood. "There will no doubt be protests from the areas where the towers are to be built," said Charles Lave, professor of economics at the University of California, Irvine. "I tend to like engineering solutions [to problems] because it's a lot easier to reduce the consequences of people's behavior than to change the behavior itself. In pursuing our goals of reduced energy consumption and decreased air pollution we have had no success in persuading people to drive less, but two engineering solutions (emission controls on cars and increased auto fuel efficiency) have worked. So I'm sympathetic to the basic approach of this proposal. But, what community would want these giant structures blocking views and creating shadows?"

At least one expert thinks the visual assault may be good for us. "We're in an era where we seem to distrust technology," maintains Steven Moore, professor of architecture at Texas A&M;. "We've been scarred. We discovered technology isn't all it's cracked up to be. There have been too many serious unintended consequences of technology, an example being atomic power. Simultaneously, technology has become increasingly invisible, [and] what seems to be happening is that society has lost its sense of cause and effect. We no longer want to see the things that make our lives easy. We're in a kind of a bind. We want electricity, we want computerization, we want all that, but we want it masked and out of the way. It's that attitude that does us the most damage, because it masks the conditions of our lives. So such a proposal as Prueitt's smog towers, as radical as it may seem, I am rather receptive to because it would tend to make the conditions of our lives powerfully present in the landscape. The message that we need to take such radical action to clean the air and generate power is something that you could no longer avoid."

An Endless Easy Breeze

Even if the populace could be persuaded to trade an aesthetic jolt for an endless breeze of clean, cool air, where could the towers be sited? These structures have expansive footprints requiring real estate not readily available in densely populated urban areas like Southern California. Prueitt suggests dual use for the land, when necessary, erecting the towers above existing development. He envisions the towers hovering silently, almost cloud-like, above golf courses, parks, playgrounds, shopping malls, schools and apartment complexes, with parking spread out under the outer skirts. Light, cascading easily through the pellucid tower skin, would provide illumination while shielding those below from ever more harmful ultraviolet rays.

Despite ample concerns, many architects and planners are intrigued bu y Prueitt's concept. "My initial reaction is one of great enthusiasm," said Willie Miller, an architect at UrbanDesign+Planning, Glasgow. "They would seem to represent a tremendous opportunity to give visual strength and form to a city's skyline. I see them at major entrances to cities, almost like defensive towers, defining routes, giving clarity to urban form, great silver-grey structures, translucent if possible, lit from within."

Alison Promin, an architect at Paradigm Affiliates in Denver, can see these utilitarian forms becoming more subtly integrated into the cityscapes - and our psyches. "If there is something that is environmentally helpful that we can treat in an architectural fashion I don't see why we can't make this thing work," she says. "In urban places where space is tight suppose all of a sudden I take one of these towers and provide a vertical park with it, a vertical staircase where we actually install platforms and viewing decks, so that instead of just moving around the tower and looking at it there's a way to make the infrastructure useful and engaging." The point is not to disguise - or for that matter, exalt - these necessary mechanical systems, but simply to embrace them as organic additions to our architectural landscape.

Prueitt's towers seem to generate more discussion than seed money. "Investors generally want to see demonstration projects erected before they commit to financing a full-sized version," Prueitt says. "Trouble is, output does not scale linearly with size. A 100 meter tower is not cost effective for producing power, although it could be useful to reduce pollution. The efficiency of a 10 meter tower is actually negative, since it cannot produce enough power to pump the water to the top." Funding for a companion demonstration project (see the accompanying story, "Plan B") has recently been provided by a Canadian venture capitol group. Construction is to begin this year.

If the convection tower idea ever finds financial backing and political blessing it would be the fulfillment of the scientific dream of harnessing the energy found in natural weather patterns in a controlled environment.

Convection in nature occurs like this: Sunlight near the Equator warms ocean water, causing evaporation. This warm, moist air rises, condensing into clouds, which then disperse their moisture as rain. The remaining dry air continues to rise into the stratosphere, circulating 30 degrees north and south of the Equator in a phenomena called Hadley Cells. When this constant flow of dry air eventually descends, compression warms it - creating the arid desert bands of the world between 15 and 35 degrees north and south latitude. For generations, scientists have looked for a way to harness the energy associated with re-humidifying dry air.

Prueitt may have found it. "Rain drops are not very efficient in scrubbing the air," he explains. "Since they [the drops] are so large most of the particulate matter in the air simply flow around the falling drops. By spraying a fine mist of water the effective surface area of a given mass of water is greatly increased, and the collection efficiency of the water is considerably enhanced. To make the system even more effective in scavenging particulate matter the water droplets can be given an electrical charge, which can increase the collection efficiency by a factor of 100." The used water, now filthy with the pollutants removed from the air, is diluted and returned to normal salinity before being pumped back to the ocean.

One Million Gallons Per Day

One million gallons of water per day, or more, would be required by the grid of sprayers across the top of each tower. In Los Angeles, the water would come from the ocean. In other cities, the water supply might be a river, or lake. Wind turbines at the base of each tower are driven by the turbulence of circulating air. When attached to electric generators they could produce nine megawatts of electricity, enough to power not only the tower's own pumps, but, under the right conditions, feed six megawatts of excess power into the region's electric grid.

"Power production depends on weather conditions," Prueitt says. "For example, at 15 percent relative humidity the towers would produce about six megawatts net of electric power each." The excess power from 100 towers (600 megawatts) could supply approximately 430,000 homes with electricity, further reducing air pollution by decreasing reliance on fossil-burning power plants.

Prueitt cautioned, however, "As the ambient humidity goes up the power output decreases." In Los Angeles, humidity is higher in the morning and lower in the afternoon; the average annual afternoon relative humidity in Los Angeles is 53 percent. The variability in power output would effect only the amount surplus energy; the towers would always be efficient enough to power their own pumps.

By admission of the city's own Air Quality Management District, Los Angeles also happens to have the worst air in the country. Clearly, we need to do something, but is Mel Prueitt tilting at convection towers? They're as expensive as they are expansive, but perhaps it's time to reexamine paradigms. Here's a technology that can mitigate some of the mess we've made, with an advantageous byproduct to boot.

Who knows? Someday we may even wax poetic on these monumental pragmatic forms, just as we do now for old wooden water towers, grain elevators, and other relics of our industrial past.

-end-

Versions of this article appeared in Southwest Airlines inflight Spirit Magazine (April, 1998), Science Spectra (No. 9, 1997), and Boys' Life (June, 1998).

Comments? Questions? Corrections? Assignments? douglaspage@earthlink.net
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