As employers eagerly investigate ways to make building ventilation systems safer, the purification of ducted airflow using UVC has become topical. There is a danger that an eager market may believe that UVC is the ‘answer’. It is not as simple as that. A more realistic perspective is that UVC at the sufficient dose to suit the application can be part of the answer in some instances. UVC can treat airflow but will do nothing for potential sources of infection in the occupied spaces be it occupants or contaminated surfaces.
For deactivating airborne biological aerosols the equipment needs to deliver a far higher dose of UVC energy. The dynamics of a treating moving air require in-duct UVC equipment where the UVC intensity and the duration of exposure are designed to deliver a dose sufficient to deactivate the target micro organism to a high efficiency. For this reason UVC treatment of the airflow in the ducting is preferable to fitting equipment within the constricted space in the air handling unit.
The parameters of the potential in-duct UVC application are important because without knowing the airflow, the duct size, ideally the air temperature range and the ducting material, selecting an in-duct UVC product is little more than a guess and any performance claim is therefore fanciful. Specifying in-duct UVC equipment is not dissimilar to specifying thermal coils in that there is some number crunching to be done first.
Understanding the parameters and having identified the target micro organism, normally but not necessarily SARS-CoV-2, a suitable UVC in-duct appliance can be specified. One of the key reasons behind this approach is to be able to model what the actual efficiency of the fitting will be in that specific application. Testing in-situ of an in-duct UVC fitting for its effectiveness against SARS-CoV-2 is difficult and expensive so inevitably confidence in the effectiveness of a UVC solution comes via the mathematics behind the modelling program.
There is a huge body of data that has been accumulated over the years where, for a staggering number of micro organisms it is known detail the size of UVC dose required to deactivate each type. It means that a UVC fitting specified to treat SARS-Cov-2 to say 99.9% will also treat other airborne micro organisms to a greater or lesser degree depending on the basic dose needed and how the micro organism ranks compared to others. UVC does not discriminate between types – it deactivates all micro organisms to some degree.