Is it real or...

An advisory committee established by the British government screened the available, relevant scientific literature to evaluate the potential of different air cleaning technologies.

Almost before it was recognized that the Covid virus could actually be transmitted through indoor air did prompt and colorful advertisements in daily press and other media market various technical solutions that supposedly could reduce disease transmission. The notion was that if a technology was able to reduce the concentration of airborne virus, it would be reasonable to also assume that the infection risk would decrease, even though most current knowledge as yet is based on other virus, including those causing several earlier SARS epidemics.

Air cleaning is one of the marketed solutions to reduce disease transmission, but air cleaning is not just air cleaning. Different principles for air cleaning may do the job, while others apparently have no effect on the airborne concentration of virus. An advisory committee established by the British government screened the available, relevant scientific literature to evaluate the potential of different air cleaning technologies.

The result was somewhat inconclusive, but indicated that some technologies might work, even though the air cleaning efficiency could be affected by several disturbing factors. One main finding was that air cleaning cannot and should not replace ventilation and that air cleaning efficiency is only marignal with well-functioning ventilation. An air cleaner's efficiency should also be assessed in relation to the use of a room and its volume. Location and general air distribution also matter as the air is cleansed mostly in a volume close to the air cleaner. 

Jørn Toftum DTU Byg

Jørn Toftum, professor DTU Byg (Technical University of Denmark)

In a densely occupied room (if that will continue to exist), it may thus be difficult to detect an effect of air cleaning far from the unit. Furthermore, poorly designed units may add ozone to the air, which is indeed an unwanted side effect.

Both REHVA and ASHRAE quickly established working groups that in little time have worked intensly to elaborate practical guidelines for appropriate building operation in the wake of the pandemic. Naturally, the guidelines overlap to some degree, but they both emphasize that recommendations are targeted specialists with at least a minimum knowledge of ventilation and air distribution. Some background knowledge is thus required to evaluate if use of a technology or initiative is meaningful in a given situation.

It is unfortunate if marketing of technical solutions to reduce disease transmission is not trustworthy. This can be caused by the vendor's lack of knowledge or a wish to make a fast profit. This may have negative, budgetary side effects, e.g. in schools with limited budgets who need to act, but do not possess the required technical knowledge to evaluate the performance in practice of a solution. As building professionals with expertise in ventilation, we have a responsibility to assess, articulate and give advice on efficient solutions and maybe even more on those that are not efficient.

This article was brought in the Danish magazine HVAC, february 2021 and translated to English by Airmaster with permission from the author.

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