Notes Regarding the Transmission of Corona Viruses and Mitigation Measures in Buildings with HVAC

In a departure from our usual message to the industry, in May’s edition of the ACR News we wanted to share some researched information about how to mitigate the spread of viruses in buildings by use of mechanical measures.


Viruses may spread between individuals, by contact with microbial carrier and also by transfer through the air.  Whilst person-to-person transmission is the main mechanism of the virus spread, we as manufacturers of HVAC must respond to this.  Implementing decent building HVAC operational practices helps to reduce the spread through the air.

Facts and measures:

Viral particles are too small to be contained by even the best HEPA filters (MERV 16).  Ventilation precautions and filter installations can be taken to minimise the spread.

  • Filters alone should not be assumed to eliminate airborne transmission risk
  • Higher fresh air ratios and increased air exchange rates help to dilute indoor contaminants
  • Ventilate and avoid re-circulation of stale indoor air and use window ventilation where possible
  • Higher humidity levels are likely to help inactivate viruses; ASHRAE recommends levels or 40-60% RH.  Changes in humidity may impact on how far into the respiratory tracts viruses are likely to deposit
  • Daylight and UV light reduces virus half-life significantly.  Spectrally tuned electric lighting, and by far the most efficacious is  UV-C light, inactivates airborne aerosolised viruses without any residue
Technical advice to reduce airborne contamination in buildings:
  • Apply measures to exhaust air flow before mixing this with fresh air for the supply air flow
  • Consider two-stage filter concept in air handlers:
    • a MERV 7 filter or higher before cooling/heating coils
    • a HEPA filter downstream of coils and fans
    • a section where UV-C radiation is applied to the air stream

Petra feels obligated to inform and support efforts to overcome the crisis by supplying effective products.  We are working on dedicated Clean Air Solution products based on a combination of staged filter concepts along with UV-C radiation to minimise the presence of dangerous aerosols carrying viruses in the air that we breathe inside buildings.



See Dietz, University of Oregon, Horve, University of California et al. (in MSystems by the American Society for Microbiology).

ACR News, May 2020