Microbial growth in heating ventilation and air- conditioning (HVAC) systems with the subsequent contamination of indoor air is of increasing concern, as airborne bacteria and fungi have the potential to adversely impact on human health by causing infections, allergic responses or toxic effects, says the International Copper Institute.
Pathogenic and toxin-producing bacteria and fungi thrive in dark, moist environments and the conditions in HVAC systems would appear to be ideal for the growth and propagation of microbes, the institute says, pointing out that microbes and the subsequent biofilms grow easily within heat exchangers.
The institute adds that intrinsic microbial biofilms on air-handling exchanger coils are associated with lowered heat transfer efficiencies and increased corrosion as well as potential odour issues.
Consequently, little or no growth of microorganisms on HVAC surfaces is optimally desired, says the International Copper Institute.
However, microbial populations present in HVAC heat- exchanger systems can be substantial. Researchers have reported bacterial concentrations of up to one-million colony-forming units per squared centimetre(CFU/cm2) on air-handling cooling coils.
According to the International Copper Institute, other researchers have shown that automo- tive and household air-conditioning units can discharge up to 2 500 CFU/m3 of bacteria and 1 000 CFU/m3 of fungi above ambient levels on initial startup.
The microbiological concentrations associated with the subsequent air stream 15 to 120 minutes after continuous use returned to background levels.
The institute points out that copper has had a long history in critical heat transfer components used in air-conditioning systems, owing to its unique combination of properties, including high-thermal conductivity, formability, corrosion resistance, ease of joining, infinite recyclability and, more recently, its antimicrobial effect.
Copper’s antimicrobial property has been used for thousands of years through the use of copper vessels to maintain uncontaminated water stores.
Pure copper and copper alloys have antimicrobial properties that kill microorganisms on contact and prevent the growth of bac- teria and fungi.
This effectiveness of copper has been proven in rigorous studies that led to Environmental Protection Agency (EPA) registration of 479 copper alloys as public health antimicrobial touch-surface products.
Antimicrobial copper products are being developed for use in hospitals to address the serious problem of hospital-acquired infections.
The antimicrobial property of copper has also found use in air-conditioning systems as it eliminates biofilm formation and build-up on the heat-exchanger surfaces, therefore reducing the concentration of contaminants in the air.