Beauty and durability are among the reasons the building community historically has selected copper
For roofing, flashings, conveying water, etc. Pipes made by forming copper sheets into tubular shapes have been found in Egyptian pyramids. The dome of the Pantheon (circa 29 B.C.) reportedly was clad with copper-alloy plates. And in 1230, Bishop Konrad ordered the roof of the cathedral in Hildesheim, Germany, be covered with copper. (Portions of that roof survived World War II, making it the oldest known copper roof in existence.)
Beauty and durability are not the only reason copper is popular in today's construction. As sustainable construction becomes more prevalent, owners and architects are turning to highly recycled and recyclable material. As a result, many LEED™ projects (certified by the U.S. Green Building Council) are being clad with copper.
Designers and engineers also are considering copper for interior applications. Most take advantage of copper's rich appearance but other uses are more utilitarian. Some of these, such as copper HVAC ducts, may benefit from copper's apparent antimicrobial properties.
HISTORY OF COPPER AS A BIOCIDE
Using copper to inhibit biological growth is not new. The Phoenicians and Carthaginians may have experimented with copper sheathing on their wooded ships to inhibit biofouling, the growth of marine organisms on ship's hulls. This would have been very effective but for cost or availability reasons, sheathing ships with copper was discontinued until the 18th century.
The idea of cladding warships with copper was presented to the British Royal Navy in 1708. In 1761 the English frigate HMS Alarm became the first ship fully sheathed with copper. It soon was apparent that reduced biological growth made copper-clad ships faster that unclad ships. Some historians speculate that Admiral Lord Horatio Nelson's victory at Trafalgar, Spain in 1805 was, in part, because of the superior speed of his copper-clad ships.
Interestingly, it was the cladding of the USS Constitution that gave birth to the copper industry in the United States. At that time the keel of the USS Constitution was laid in 1797, all copper bolts, spikes, nails and sheathing were imported from England. When many of the English bolts proved faulty. Paul Revere offered to make new bolts at his copper foundry. The Navy recognized in importance of having and American source for strategically important sheathing. As a result, in 1801, under a government contract, Revere rolled the first copper sheets at his mill along the Neponset River in Canton, Mass. In 1803, the USS Constitution was recoppered with sheathing rolled by Revere-and the rest is history.
What does the sheathing of ships have to do with HVAC systems and IAQ? Very little, other than it provides in interesting lead-in to the problem and a potential solution.
Biological air pollutants exist everywhere-in homes, places of employment, restaurants, hospitals, and nursing homes, schools, etc. They originate fro outdoor air and human or animal occupants, including pets, insects, and vermin. Except to those who suffer from allergies, historically IAQ has been of little or no concern. However, the 1976 outbreak of Legionnaire's disease on Philadelphia changes the public's attitude. (Legionnaire's disease is a pneumonia caused by Legionella, a bacterium primarily found in warm-water environments) Overnight, the fact that biological aerosols, or bioaerosols, can cause serious health problems and even death was brought home.
Less widely reported but equally serious is the incidence of tuberculosis (TB) TB is an airborne infection caused by the bacterium Mycobacterium tuberculosis. The U.S. Department of Labor estimates nearly one-third of the world's population is infected with TB. In 2003, the Center for Disease Control reported 14,874 cases of TB in the United States. Although the reported number of cases of U.S. TB has been reduced by more that 43 percent since the 1992 peak, modern construction techniques are contributing to other problems.
In an effort to conserve energy, buildings are being made "tighter," reducing air exchanges. Pollutants and disease-causing organisms are trapped and able to multiply. The results are poor IAQ, sick building syndrome and increased allergic reactions.
BIOLOGICAL CONTAMINATION OF HVAC SYSTEMS
Air distribution systems are not the only source of these organisms. As many health experts agree, there is a potential for common indoor bioaerosols to deposit, and be available on HVAC components.
Like all living organisms, fungi, bacteria and molds require a "friendly environment" to grow and promulgate. Such an environment includes proper temperature (usually between 40 and 120 F (4 and 49 C) moisture and food-conditions that are present in heating and air-conditioning ducts.
Therefore, it is not surprising that among findings of a 1995 study, "HVAC Systems as Emission Sources Affecting Indoor Air Quality: A Critical Review, EPA Project Summary," by S. Batterman and H. Burge, the following was included: "Many HVAC components can act as direct or indirect sources of particles and/or volatile organic chemicals. These can affect IAQ under some conditions. Most prominent is the occurrence of biological growth and bioaerosol generation in the presence of moisture… ."
FIXING THE PROBLEM
What can be done to reduce the exposure to bioaerosol contaminants? Currently accepted responses include:
- Provide adequate ventilation to prevent HVAC systems from acting as reservoirs for fungi, mold and bacteria.
- Control moisture levels between 30 and 50 percent to prevent condensation.
- Reduce or eliminate sources of biological pollutants.
Cleaning and decontamination of residential and commercial HVAC systems has become a large industry. Despite this, the U.S. Environmental Protection Agency (EPA) states: "Duct cleaning has never been shown to actually prevent health problems. EPA does not recommend that air ducts be cleaned except on an as-needed basis because of the continuing uncertainty about the benefits of duct cleaning under most circumstances".
With respect to decontaminating HVAC systems, EPA notes, "There remains considerable controversy over the necessity and wisdom of introduction chemicals biocides or ozone into duct work". The American Conference of Governmental of biocides as a substitute for removing microbial growth and settled biological material is not considered acceptable".
As of to add insult to injury, currently there is no inexpensive or easy way to detect the presence of or determined they type of biological contaminants in an HVAC system.
So, what can an architect, engineer or building owner do to improve IAQ? There are many things, but one unique approach that will help while offering attractive aesthetics is copper ductwork.
ANTIMICROBIAL PROPERTY OF COPPER
A 1973 literature search by Battelle Columbus Laboratories, Columbus, Ohio, examined 312 documents that demonstrated small amounts of copper could control the development and promulgation of many harmful microbes. A 1989 paper, "The Molecular Mechanisms of Copper and Silver Ion Disinfection of Bacteria and Viruses," by R.B. Thurman and C.P. Gerba found in CRC Critical Reviews in Environmental Control, Vol. 18, Issue 4, reviewed more that 120 studies of copper antimicrobial properties. They concluded these mechanisms are very complex; they take place inside cells and in the spaces between cells; they include catalytic oxidation and reduction, cell wall interactions, etc.
According to A. Lewis and C.W. Keevil in their 2004 paper, "The Viability of Antimicrobial Copper As A Hygienic Material for HVAC System Components", for the International Copper Association Ltd,: "No matter what the precise molecular mechanisms may be or how they may work in synchrony, the point to be emphasized here is that the literature unquestionably confirms that copper is antimicrobial in aqueous and humid air environments."
Studies by S.A. Wilks and Keevil in 2003 (see figure A) at the School of Biological Sciences, University of Southampton, Hampshire, England, demonstrated that Listeria monocytogenes was inactive after 60 minutes of exposure of copper.
This is not an isolated study. A study conducted by J.O. Noyce and Keevil, "The Antimicrobial Effect of Copper and Copper Based Alloys on Methicillin Resistant Staphylococcus aureus" at the University of Southampton in 2004 showed that copper can inhibit the "superbug" Staphyloccus aureus. Other studies have shown that the survival rate for Enterococcus faecalis after 96 hours on copper is 35 percent or less that one-half the survival rate on stainless steel (75 percent) for the same period and conditions.
While most studies have compared the antimicrobial properties of copper and copper alloys to stainless steel, the 1973 literature search by Battelle Columbus Laboratories presented 21 studies comparing zinc with copper. This is significant because most HVAC ducts are made of galvanized (zinc-coated) steel, not stainless steel. These studies showed that zinc is much less effective and does not provide a meaningful hygienic effect.
Based on currently available test results, a strong case can be made that the use of copper in HVAC systems could be hygienic, reduce the level of unwanted airborne biological pathogens and improve IAQ. Arguments can be made to provide antimicrobial copper filters in HVAC systems and use copper fin and tube heat exchangers. However, using copper for what often is the most visible part of an HVAC system-exposed ductwork-combines function with aesthetics.
The most common objections to copper ductwork are cost and "we have never done it before". The cost of copper ductwork obviously will be greater that that for galvanized ducts. In today's marker, the metal cost alone would make a 10-inch (254-mm) copper duct about $3 per foot more than a duct made from galvanized steel. Further, because copper ducts are not yet widely available, fittings and installation would probably command a premium. Nevertheless, if all costs, environmental impacts and aesthetic issues are considered the "gap" between copper and galvanized steel narrows. When the potential for better IAQ and health issues are added, the choice to use copper may be economically justified.
While copper ductwork may reduce some bioaerosol contaminants, it will not cure all IAQ problems. Additional studies are needed to quantify and more fully understand the extent to which using copper in HVAC systems can improve air quality. Currently, the copper industry is conducting such studies and pursuing EPA approval to make performance and health claims.
Until more is known about the benefits of copper ion HVAC systems, the building community should consider copper ductwork for its richness, beauty and aesthetics, which cannot be obtained with other materials. When the environmental friendliness of copper is added to the equation, using copper for exposed ductwork in upscale projects makes sense. Any improvement in IAQ is only an added benefit.
I have a project that is specifying copper spiral duct but no one seems to know what distributor handles this. I need this info asap. We are located in North Myrtle Beach. SC however I just need to know where we can purchase this product
By Tina Jenkins W/ Atlantic Htg & Clg, Inc
I am also looking for information on suppliers for copper ductwork. So far all the contractors I spoke with scratch their heads and said they have never heard of such a thing.
In regards to the article dated 2004 "The power of copper", we would like to inform any individual who may be interested, that a new approach on the copper air duct system has already been realized.
In March 2010, a full system of copper air ducts has been constructed and installed in a central office building in Athens /Greece.
Should there is any interest for more details, do not hesitate to contact us:
Director of Hellenic Copper Development Institute
By NICK VERGOPOULOS