People are spending more time indoors than ever before. Older buildings are accommodating more employees than they were designed for and consequently Indoor Air Quality has become a serious health topic. It has been proven that the air we breathe can make us feel unhealthy and lethargic. The air that we breathe can aggravate allergies and induce illnesses. IAQ can be affected by microbial contaminants (mould, bacteria), gases (including carbon monoxide, radon and volatile organic compounds) that can induce adverse health conditions. Indoor air is becoming an increasingly more concerning health hazard than outdoor air. Using ventilation, filtration and source control are the primary methods for improving indoor air quality in most buildings. Unfortunately most air handling systems create ideal environments for microbial contaminants to grow and propagate. The warmth and moisture found in the Heating, Ventilation and Air Conditioning systems of households and office buildings make the perfect breeding ground for airborne moulds, microorganisms and bacteria. These HVAC systems also provide an ideal way to circulate viruses and germs around an entire office building or home in a relatively short time.The use of Ultra Violet in air handling units has become an efficient solution in de-activating Mould, Mildew, Bacteria and Viruses.
The bactericidal effects of ultra violet radiation were investigated in the 19th century. In the early 1940’s William F Wells and colleagues demonstrated the ability of ultra violet germicidal irradiation (UVGI) which is now called germicidal ultra violet (GUV)to prevent the spread of airborne infections. Ultra Violet light had generally been used to disinfect surfaces, water and other liquids. Germicidal disinfection is delivered at the 254 nanometre wavelength in the light spectrum and is known as UV-C. Ultra violet radiation deactivates microorganisms by penetrating the cell wall and disrupting the DNA structure thereby rendering them unable to infect or reproduce. Continuous dosages over time will result in death of the organism. The general rule of thumb is intensity (of the UV light) over time (the amount of time the organism is exposed to the rays), much like one running ones finger over a flame; if it’s done too fast nothing will happen but if you run it over slowly you will get burnt. Ultra Violet Germicidal Irradiation is effective in deactivating microbial agents such as Influenza A virus, Bacteria such as Mycobacterium tuberculosis, Legionella pneumophila and Fungi, including Aspergillus niger spores, Rhizopus nigricans spores and Listeria monocytogenes. The list is long but these are some of the more common microbiological agents. All microbiological agents are susceptible to Ultra Violet rays.
To determine the ultra violet needs for an HVAC system one needs to know the sanitary requirements and the velocity of the airflow through the system. Based on this factor GUV units can be supplied with single or multiple lamps and varying wattages. Many GUV units consist of an extruded aluminium framework with multiple lamps that are installed inside the HVAC unit. Installation of GUV units is most effective when the ultraviolet radiation shines on the cold air side (wet side) of the air conditioner evaporator coil. This keeps the evaporator coil clean by reducing the normal mould and algae growths that can act as an incubation area for bacteria. This also prevents the accumulation of mould and fungi on the coil and filters that can inhibit air flow and thus increase electricity and cooling costs.
Most HVAC systems in South Africa are not installed with GUV units and therefore there is no standard GUV unit. In most instances UV-C units need to be custom manufactured to the specifications of the air handling unit. Often there is no room for a lamp framework or there is limited access to the air-conditioning system. In situations like this an ‘external unit’ is fabricated where the ballast and starter are housed in a base that is mounted to the side of the filter block with the lamp(s) extending inside.
In other situations a complete ‘stand-alone’ unit can be manufactured and placed directly into the duct or ducts. These in-duct and on-coil fixtures can be mounted in various configurations for optimum pass-by air decontamination, and/or to irradiate cooling coils and drain pans.
The probes (UV-C lamps) should be wiped clean once per year. Depending on the manufacturer of the lamps replacement should be once every two years, usually the first quarter of the third year. A UV-C lamps output generally deteriorates about 12% to 15% per year, and the UV-C output after two years is about 67% of a new lamp.
Exposure to the germicidal wavelengths of UV light can cause sunburn and can produce extremely painful inflammation of the cornea and damage to the retina. Prolonged exposure can cause blindness. Maintenance schedules are one of the most important factors in using UV-C or GUV units for prevention.
For more inforamtion on Sani UV-C units please do visit www.ozoneuv.co.za or contact me at
011 462 5525