Issue link: https://hi.iaq.net/i/866954
The main components of a UV disinfection system are mercury arc lamps, a reactor, and ballasts. The source of UV radiation is either the low-pressure or medium-pressure mercury arc lamp with low or high intensities. The optimum wavelength to effectively inactivate microorganisms is in the range of 250 to 270 nm. The intensity of the radiation emitted by the lamp dissipates as the distance from the lamp increases. Low-pressure lamps emit essentially monochromatic light at a wavelength of 253.7 nm. Standard lengths of the low- pressure lamps are 0.75 and 1.5 meters with diameters of 1.5 to 2.0 cm. The ideal lamp wall temperature is between 95 and 122° F. VII. UVGI Air Disinfection UVGI Air Disinfection systems are mainly grouped into four main types: 1. In-duct UV systems 2. Unitary UV systems 3. Upper-room systems (Passive) 4. UV barrier systems (Passive) The upper-room and barrier system are passive disinfection systems that depend on local room air currents while in-duct UV system is a one directional forced air system with minimal dose exposure. These systems require the use of filters to control airborne contamination, especially when it comes to spores. UVGI is not a stand-alone solution to air contamination problems but is an adjunct when compared to the DFS system which is a comprehensive, high efficiency three pollutant category hybrid air filtration system. Some of the air stream disinfection challenges are limited to the exposure time which depends on the airflow and dimensions of the ducts. The DFS filtration system unlike the air stream system is designed to capture and constantly expose captured microbe throughout the filter media to continuously deactivate and inhibit the microbial growth within the system leaving the air passing through free from contaminants. While some evidence demonstrated that UVGI is effective at reducing disease incidence comes mostly from upper-room UV systems, other studies on the incidence of respiratory infections at a daycare center showed a negligible reduction in illness (Dionne 1993). VIII. Disadvantages of UV • Low dosages may not effectively inactivate some viruses, spores, and cysts. • Organisms can sometimes repair and reverse the destructive effects of UV through a "repair mechanism," known as photoreactivation, or in the absence of light known as "dark repair." • A preventive maintenance program is costly and necessary to control fouling of tubes. • UV disinfection is not as cost-effective in comparison with the DFS filtration system. • There is no measurable residual to indicate the efficacy of UV disinfection. • UV systems don't work on capturing particulates from the air of any size • UV passive systems doesn't address contaminants outside the HVAC, Coils or in room air