Maximising Ventilation in New Builds

COVID increases need to maximise ventilation in new builds

Our understanding of how the SARSCoV-2 virus, responsible for COVID-19, is transmitted from person to person has changed significantly since the start of the pandemic. Initial belief was that the virus was predominantly transmitted from touching contaminated surfaces and being exposed to someone sneezing and coughing. Scientific evidence has now confirmed that the airborne transmission of the SARS-CoV-2 virus is not only a significant, but likely the major infection pathway involved in the spread of COVID-191,2,3,4,5 . Airborne transmission of the virus is where virus particles move from person to person in tiny aerosol or water droplets exhaled by an infected person. Aerosol particles exhaled by an infected person can remain suspended in air for a long period of time when compared to the heavier droplets expelled during coughing and sneezing. As a result, they can build up in a small unventilated area. Also depending on the air movement patterns of a particular area, exhaled aerosol particles can travel a significant distance, much further than droplets generated by a sneeze or cough and much further than the 1.5 metre physical distancing requirements currently mandated in public settings. Effective strategies available to control the spread of the SARS-CoV-2 virus include vaccination, physical distancing requirements, and the quarantining of infected persons. Research has shown that increased ventilation in a building can reduce the chance of influenza spreading in a building. A study published in 2019 found that providing even minimum levels of outdoor air ventilation reduced influenza transmission as much as having 50-60% of the people in a building

vaccinated6 . Ventilation is a key strategy in reducing airborne infections, however, it’s not the only factor. Not only does the size of a room and the number of people present impact the probability of COVID-19 infection, but also the specific ventilation characteristics of the room. It stands to reason that an individual present in a small unventilated room with an infected person, who is exhaling infected aerosol particles containing the SARS-CoV-2 virus, will be exposed to a far greater number of virus particles, as the level builds up in the room over time. As such the uninfected individual will inhale significantly more SARS-CoV-2 virus particles and is more likely to become infected compared to the same scenario where there is a good ventilation/extraction system, which is replenishing ‘stale’ air with fresh external air. The impact of poor ventilation and the number of individuals present in such an area was highlighted in the highly publicised outbreak where an indoor gathering of 30 individuals at a home in Western Sydney resulted in 24 individuals becoming infected with the SARS-CoV-2 virus7 . Specific airflow requirements for indoor settings are detailed within Australian Standard 1668.2-20129 The use of ventilation and air conditioning in buildings.

Part 2: Mechanical ventilation in buildings8 .

This standard details the minimum airflow requirements based on occupancy, specifically the net floor area per person (m2), and the minimum outdoor airflow rate (L/s/. person). It is important to understand that these minimum airflow requirements were developed to minimise the potential build-up of odours from occupants and carbon dioxide (CO2) generated from the exhaled air of those present within these indoor settings. High CO2 levels are associated with fatigue and poor concentration, not something conducive to effective learning in the school room environment or productivity in the workplace. It must be made very clear; these minimum airflow requirements were NOT developed to reduce the risk of airborne disease transmission such as COVID-19, and a low CO2 level is not a reliable indicator of a low transmission risk. It has been shown that to reduce the risk of airborne disease transmission the effective air change rate within these indoor settings is required to be significantly higher than those prescribed within AS 1668.2-2012. Ventilation systems were not designed with sickness in mind, the guiding principle in the design of most new buildings is energy efficiency, that is keeping heating and cooling costs to a minimum not minimising airborne disease transmission. As a result, most building designers will look to rely on windows and doors for ventilation, and where mechanical ventilation systems are utilised, they are designed only to provide the minimum ventilation requirements detailed within AS 1668.2-2012. Heating and cooling external air also requires energy and a cost associated with it, as such mechanical ventilation systems may only be designed to recirculate air within a space, and not supply external fresh air.

If natural ventilation is a driver in the building design, ventilation is not a high priority. Relying on windows and doors for ventilation to control transmission of disease is risky as it requires the occupants to keep windows open, something that is very difficult to comply with on either hot or cold days. Designing mechanical ventilation systems to only meet the minimum ventilation requirements means that ventilation cannot be manually increased above and beyond design specifications. So, what can you in the construction industry do to maximise ventilation in new buildings? You can design buildings that follow these basic guidelines. 1. If you are relying on natural ventilation (windows) make sure that you design rooms to allow cross draught ventilation by installing windows in more than one side of a room. This gives natural ventilation the best chance of working. If this can’t be achieved, then consider mixed mode ventilation with heat recovery. 2. Make sure mechanical ventilation systems are designed to provide external fresh air into living spaces and have spare capacity so that it can increase room ventilations rates above the minimum ventilation requirements detailed within AS 1668.22012 that have variable speed dampeners

(VSDs) installed for controllability. 3. Ensure that air filtration systems associated with mechanical ventilation systems can filter out virus particles. This usually means a filtration system with a minimum MERV 14 rating if practical. 4. Understand what impact you have as the designer or architect for your client to effectively operate and maintain a mechanical ventilation system. When considering your mechanical ventilation system PLEASE make sure you design it and the building around it so that actual planned maintenance on the system can be done. We have seen examples where accessible components of the system such as dampers were placed behind walls.

It has been shown that to reduce the risk of airborne disease transmission the effective air change rate within these indoor settings is required to be significantly higher than those prescribed within AS 1668.2-2012.

Andrew Orfanos

National Division Director, Occupational Hygiene, VA Sciences

Simon Witts

National Division Director, Engineering, VA Sciences

References

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J. Identifying airborne transmission as the dominant route for the spread of COVID-19. Proceedings of the

National Academy of Sciences 117, 14857–14863, doi:10.1073/pnas.2009637117 (2020). DOI: 10.1073/ pnas.2009637117 3. Wang CC, et al. Airborne transmission of respiratory viruses. Sciences. 2021; 373, 981. www.science.org/doi/10.1126/science.abd9149 4. Morawska, L. J., & Cao, J. (2020). Airborne transmission of SARS-CoV-2: The world should face the reality. Environment International, 139, 105730.

DOI: https://doi.org/10.1016/j.envint.2020.105730 5. Anderson EL, et al. Consideration of the aerosol transmission for COVID-19 and public health.

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DOI: https://doi.org/10.1038/s41598-019-38825-y 7. https://www.abc.net.au/news/2021-06-28/vaccinatedattendees-west-hoxton-birthday-party-avoidcovid-19/100249612