Purification
Air quality HVAC & Building Automation
Use of UV
Amongst all the reams of hastily compiled guidelines issued by various sectors about adapting ventilation systems to enable the return to work, in-duct UVC air purification gets the occasional mention. Whilst this is encouraging, in-duct UVC should not merely be seen as a quick fix to help make workplaces safer from Covid-19. It is much more than that. In-duct UVC is a long term investment in the workplace environment that pays back even in non-covid times by delivering lower absenteeism costs. In that context the supply of purified air, free of viable SARS-CoV-2 is a short term bonus.
The recent history of UVC in HVAC systems is interesting. Sick building syndrome was much discussed in recent decades with one of the contributing factors identified as centralised building ventilation systems, and in particular the microbial contamination that can accumulate in cooling coils and drip pans. This was a particular issue in the more southerly states of the USA where higher ambient humidity and temperatures are typical. Although the cooling coils would be protected by air filters, if the source of the contamination was the cooling coils then the filter stages being fitted upstream of the source, were not in a position to offer any benefit. UVC was widely marketed as a solution to this problem and by basking cooling coils in UVC light microbial growth could be prevented.
A number of academic studies were carried out to quantify the effectiveness of this approach and there seemed to be broad consensus that UVC coil cleaning was both effective at keeping coils free of microbial growth and that there was a significant reduction in workplace absenteeism. One such double blind study by Montreal Chest Institute (part of McGill University in Montreal) which was published by the Lancet, described how basking of cooling coils in UVC reduced bacteria on irradiated surfaces by 99% and for the building occupants the overall sickness rate was reduced by 20% and respiratory symptoms by 40%.
Whilst the effectiveness of UVC coil cleaners is well understood, it should be remembered that this effect derives from continuous exposure of surfaces, preventing microbial growth and the subsequent entrainment of viable microbial particles from those surfaces to the airflow. It does not follow that a UVC coil cleaner type fitting will also be equally effective at treating airborne bioaerosols. That 99% figure does not apply to treating airborne micro organisms.
Use of UV
Amongst all the reams of hastily compiled guidelines issued by various sectors about adapting ventilation systems to enable the return to work, in-duct UVC air purification gets the occasional mention. Whilst this is encouraging, in-duct UVC should not merely be seen as a quick fix to help make workplaces safer from Covid-19. It is much more than that. In-duct UVC is a long term investment in the workplace environment that pays back even in non-covid times by delivering lower absenteeism costs. In that context the supply of purified air, free of viable SARS-CoV-2 is a short term bonus.
The recent history of UVC in HVAC systems is interesting. Sick building syndrome was much discussed in recent decades with one of the contributing factors identified as centralised building ventilation systems, and in particular the microbial contamination that can accumulate in cooling coils and drip pans. This was a particular issue in the more southerly states of the USA where higher ambient humidity and temperatures are typical. Although the cooling coils would be protected by air filters, if the source of the contamination was the cooling coils then the filter stages being fitted upstream of the source, were not in a position to offer any benefit. UVC was widely marketed as a solution to this problem and by basking cooling coils in UVC light microbial growth could be prevented.
A number of academic studies were carried out to quantify the effectiveness of this approach and there seemed to be broad consensus that UVC coil cleaning was both effective at keeping coils free of microbial growth and that there was a significant reduction in workplace absenteeism. One such double blind study by Montreal Chest Institute (part of McGill University in Montreal) which was published by the Lancet, described how basking of cooling coils in UVC reduced bacteria on irradiated surfaces by 99% and for the building occupants the overall sickness rate was reduced by 20% and respiratory symptoms by 40%.
Whilst the effectiveness of UVC coil cleaners is well understood, it should be remembered that this effect derives from continuous exposure of surfaces, preventing microbial growth and the subsequent entrainment of viable microbial particles from those surfaces to the airflow. It does not follow that a UVC coil cleaner type fitting will also be equally effective at treating airborne bioaerosols. That 99% figure does not apply to treating airborne micro organisms.
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