When 221 hotel guests fell ill at the American Legion's bicentennial event in 1976 with symptoms of fever and coughing, resulting in 34 deaths, scientists were shocked to learn that the infection hadn't come from some outside source but from within the hotel itself—more specifically, from the building's air conditioning system.
Dubbed Legionnaires' Disease as a result of that fatal outbreak, the strand of bacteria behind the Philadelphia epidemic still thrives in some cooling systems today. But it's not the only thing. Moist, dark and virtually impossible to clean, heating, ventilation and air conditioning (HVAC) systems are a known breeding ground for a slew of unwanted organisms, from molds and fungi to any number of harmful microbes.
But all that could change. Research is now under way to test whether copper—a proven antimicrobial agent—can be used in the fabrication of HVAC systems to stop pathogenic bacteria before they find their way into the airstream.
The federal Environmental Protection Agency (EPA) has already declared that, as a touch surface, the red metal is effective in the fight against a number of harmful microbes. Now, in two separate studies funded by the Defense Department, researchers hope to prove that copper can improve air quality as well.
The tests, which look to see whether or not copper in HVAC systems can reduce the spread of harmful microbes, are twofold. One, performed within a controlled and calculated laboratory environment, is taking place in the Arnold School of Public Health at the University of South Carolina; the other, a study of performance in a real-world setting, tests competing HVAC systems in an active military barracks in Columbia, S.C.
Although no conclusive results have been reported yet, the principal investigator for the study, Gene Feigley, said there are reasons to expect that systems made with copper will outshine now-commonplace aluminum in the trials.
"There's lots of evidence from the laboratory and from traditional use that copper makes a difference. If you talked to people who were installing air conditioning units 50 years ago, they'll tell you that with the copper units there weren't a lot of indoor air quality complaints. That's anecdotal, but it can be important," said Feigley, a professor of environmental health sciences at the University of South Carolina.
Heat exchangers that use copper coils, fins and drip pans also might be easier to recycle than their aluminum counterparts, according to Ed Rottmann, vice president of sales, marketing and product development at the ACR Tubes Americas division of Luvata Oy. Both metals are 100-percent recyclable in their purest form, but aluminum heat exchanger parts often contain added flux or brazing compounds that need to be stripped in the recycling process—an easy procedure, but another step and, therefore, an added cost.
Also benefiting copper in the copper-vs.-aluminum debate is the question of energy efficiency, copper promoters contend. Copper has a higher conductivity level than aluminum, but that's only part of the story. A HVAC system covered in mold spores is far less efficient than a clean one, so while copper and aluminum systems might perform the same directly out of the box, after years of potentially organic buildup an antimicrobial copper system is likely to boast a better performance, Rottmann said.
"A lot of the energy efficiency certifications are done when the equipment is purchased or when it is brand-new in the factory, but as there becomes increasing awareness of how effectively that unit operates over time, it will drive the market (for copper parts) at an accelerated pace," he said.
However, copper has its pitfalls, too. Heavier than aluminum, copper has consistently lost market share in any application where weight is a consideration such as in HVAC systems in personal vehicles. Hugo Ravesloot, head of business development at Norsk Hydro ASA's automotive business sector, estimates aluminum has a 100-percent market share in the automotive HVAC sector.
"I think perhaps the reason we got away from using copper originally was aluminum is lighter, so the people doing the installations probably didn't want to carry around copper because it is heavier," Feigley said.
But copper's weight on one's pocketbook is the largest deterrent to its wide-scale adoption. "The uses of copper have increased substantially, with the electronics revolution and more and more uses in computers and other types of circuitry, so that the price of copper is much higher than aluminum," Feigley said.
You don't have to tell that to Dean Bowlin, director of coil products at High Ridge, Mo.-based commercial and industrial HVAC manufacturer DRS Marlo Coil. He said copper was always the product of choice for his company until last year, when prices skyrocketed.
"Copper was at an all-time high within the last year, and once it was approaching $4 a pound—almost $5 a pound once we pay a (fabrication) charge—people were exploring aluminum to get away from the copper because it was so God-awful expensive," he said, noting that while his company has grown accustomed to using copper, during times of high prices it simply isn't possible. "It is purely cost driven."
Marlo wasn't the only company to rethink its use of copper this year. Late this summer, Bohn de Mexico SA de CV, a top supplier of HVAC components in North America, elected to use aluminum instead of copper tubes, citing potential cost savings.
"(Aluminum) finstock is very much a commodity, which is going to be very difficult for anyone to replace because it's very cheap in the marketplace. To replace that with copper—that's a hell of a challenge," said Ravesloot, whose company signed on to deliver 150,000 pounds of aluminum tubing to Bohn as it moves away from copper.
Even so, Feigley remains optimistic. "Given the problems we have now with indoor air quality, I would think in the long run finding good ways of controlling bacteria and fungal contaminants in indoor air can more than pay for itself."