Getting Technical less than 316 grade which obviously limits ductwork installations to those made with suitable corrosive resistant materials .
Also , many experiments and trials have found that ozone concentrations in air needed for rapid duct cleaning often exceed the top safety limit of 0.3 ppm for 10-minute periods . Blowing fresh air through the ozone treated ducting to ensure reduction of ozone levels to below safety and odour limits throughout ductwork and air-conditioned areas becomes too long a period during which these areas cannot be occupied . UV in the 185 nm area creates small amounts of ozone from atmospheric oxygen . This has been known for many years but only recently been developed into reliable cost-effective UV / ozone combination units . Modern UV bulbs or lamps , as they are called , generate up to 2 % ozone by weight of the air passed over them equating to 0.04 ppm on normal atmosphere which is enough , at the very low levels where ozone is effective , for UV / ozone units to provide two separate and rapid air disinfecting actions and highly effective de-odorising .
Both UV and ozone have been used in hospitals for many years to prevent infections from airborne pathogens , for example tuberculosis bacteria which are prolific in South Africa . Air treatment with UV alone can accomplish acceptable air disinfection but UV does not possess the powerful deodorising properties that ozone has .
In the past , feeding ozone into conditioned air spaces and keeping it evenly mixed at the correct low-level concentrations has been difficult to achieve . Now , however , UV / ozone combination units in which UV both attacks pathogenic microorganisms and generates the correct amounts of ozone provide elegant solutions to previous control problems .
Killing micro-organisms is faster and more comprehensive with the combined but different biocidal activities of UV and ozone . However , it is only the ozone which removes the
Courtesy Ozone Service Industries . distinctive odours of staleness and chemical disinfectants widely associated with hospitals .
Hospitals are only one example of where UV / ozone units disinfect and deodorise indoor air . The units can operate in temperatures ranging from frozen food storage to gymnasium saunas and are also unaffected by high or low humidity . Private homes , laundries , food processing and storage plants , hotels , theatres and , in fact , any indoor areas where people work , relax or congregate often need the benefits of efficient air disinfection and deodorising which safeguard and improve the quality of life . Then , when life is finally ended , the necessary mortuary facilities need similar air treatment as shown in Figure 2 where indoor cooled air is continuously re-circulated through wall mounted UV / ozone units .
Figure 2 : A wall UV / ozone unit installed at ceiling height in a mortuary .
Figure 2 also illustrates how these types of UV / ozone air treatment units are now regarded as ‘ mount and plug in ’ appliances . However , UV / ozone unit selections are not as simple as lighting or heating units . Air circulation rates and ozone levels needed must be accurately calculated for sizing each UV / ozone unit RACA
www . hvacronline . co . za RACA Journal I September 2021 49