Latin America. The effects of ultraviolet radiation on nature are well known, just remember that where the sun acts directly there is no proliferation of fungi or bacteria. Ultraviolet radiation is currently applied in air conditioning systems in two completely different ways: direct irradiation of surfaces and in photo catalysis processes.
This article aims to explain in a very summarized way these two applications.
Germicidal ultraviolet light
The germicidal action of ultraviolet irradiation has been known and applied for more than a century. The range of radiation with wavelength between 200 and 300 nm, known as UV-C, is very efficient in the deactivation of fungi, bacteria and molds, if provided in the appropriate dose, remembering that the dose depends on the time of exposure and the intensity of the radiation.
Another very important aspect of ultraviolet radiation is that it is harmful to humans and can cause burns on the skin, ocular cornea and retina. Therefore, exposure to UV radiation should be avoided. Many countries have strict legislation prohibiting direct exposure to ultraviolet light.
Germicidal ultraviolet light (UVGI) is applied in air conditioning systems for surface disinfection, finding greater application in the cleaning and protection of coils. Its use as an air purifier is limited by the high speeds adopted in the ducts, which require high-power irradiation to ensure their effectiveness, or even stretches of long ducts equipped with UV-C lamp. It is important to note that UVGI only removes microorganisms that pass through light, acting as a filter, that is, it serves to decrease the lower concentration of contaminants.
An interesting analogy is to imagine that we are working with sinks of point contaminants, which would be the return openings, through which the air from the room is sucked to be led to the "air purifier".
However, because it is a well-known technology and in which there is an applicable standardization, although exclusively for surface protection, it is to be recommended as a solution for air purification in the built environment.
PHI Technology – Photo Catalysis
Ultraviolet light from the sun's rays, when it radiates particular metal oxides from the soil, ionizes water vapor and oxygen molecules, which bind into hydrogen peroxide. Hydrogen peroxide is highly reactive and one of the best-known germicides.
In nature hydrogen peroxide is found in concentrations ranging from 0 to 50 ppb (0 to 0.05 ppm) and, the higher its concentration, the cleaner the site, due to the oxidative potential of peroxide, which reacts with organic and inorganic gases, kills fungi and bacteria, as well as deactivates viruses suspended in the air or on surfaces. This phenomenon is known as photocatalysis (PCO of Photo Catalytic Oxidation) and, replicated in equipment, has been successfully applied for more than thirty years in the purification of environments. RGF Environmental Group's air purifiers, which use photocatalysis their own patented process, hydro photo (PHI) are sized to ensure a concentration of 20 to 50 ppb in the treated environment, simulating the best natural conditions. All favorable results of the efficacy tests performed had this concentration level as a minimum level.
Going back to the previous analogy, applying a catalyst photo, which is a gas generator that is carried into the environment, would be as if we had spread a multitude of sinks throughout the built environment. It is the only way to effectively obstruct the path of airborne transmission, in addition to the use of personal protective equipment, such as face protection masks.
It is important to remember that multicellular beings have natural protection against hydrogen peroxide. In normal concentrations, it doesn't hurt us. The limit value of the concentration of hydrogen peroxide admitted for the occupation of daily work is 1000 ppb, that is, twenty times higher than the highest desired concentration. In addition, the concentration limit above which health damage can be expected is 75,000 ppb. Far from what is to be considered.
This brief article concludes on the substantial differences that exist between germicidal ultraviolet irradiation and photocatalysis processes, in order to have the appropriate precautions at the time of decision making in an investment in the use of them in air conditioning systems.
* Article by Ricardo Cherem de Abreu, Technical Director of Dannenge International.
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