Using Ultraviolet Radiation Against COVID-19
Ultraviolet Germicidal Irradiation or UVGI can complement high-efficiency filters. While filtering captures harmful particles like viruses and bacteria, UVGI kills them by destroying their DNA. Ultraviolet radiation with a wavelength of 200 to 280 nm is called UV-C, and it is the most effective against viruses and bacteria. The germicidal effect is maximum at 265 nm, and most UVGI systems use 253.7 nm, which is close to the optimal value.
UVGI disinfection technology can be classified into four main types. The basic principle is the same - killing pathogens with UV-C radiation - but the application method changes:
- In-duct air disinfection
- Upper-air disinfection
- In-duct surface disinfection
- Portable room decontamination
More than one method may be viable for your HVAC system, and NY Engineers can help you find the best option.
In-duct air disinfection uses arrays of UV lamps in HVAC equipment or air ducts, which apply a high dose of UV-C as the air passes by. They are normally designed for an airspeed of 500 fpm, with a minimum irradiance zone of 2 feet and an exposure time of 0.25 seconds. According to ASHRAE, this type of UVGI should be coupled with at least MERV 8 filtration.
Upper-air disinfection is normally used in occupied spaces at least 7 feet tall, where the walls and ceilings have a low UV reflectivity. The ventilation system should maximize air mixing to make this method more effective, and supplemental fans are used when the existing ventilation is not enough.
In-duct surface disinfection is similar to the first method, but UV lamps are installed along ducts, drain pans, cooling coils, and other wetted surfaces. This method has a longer exposure time than the in-duct air disinfection rate, which means it can use a lower UV irradiance.
Portable room decontamination is typically used for surfaces since the unit is portable and fully automated. These UVGI systems are very effective, and they have been used successfully against pathogens more resistant than the 2019 coronavirus.