homenews and insights how to use building services to help prevent the spread of covid 19

How to use building services to help prevent the spread of COVID-19

By Dr Andrew Eaton
11 May 2020

Product Marketing Manager

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The recommendations given in this blog are taken from the “REHVA COVID-19 guidance document, April 2, 2020”1. That document may be subject to revision if new scientific evidence is reported and readers are urged to visit the REHVA website for the latest advice. It is recommended that readers also act in conjunction with advice from the W.H.O. on “Getting your workplace ready for COVID-19”2. It should be noted that in the absence of evidence regarding SARS-CoV-2 (COVID-19) the advice listed here is mostly based on evidence relating to the previous SARS-CoV-1 epidemic.

Who is this advice for?

This advice is intended for anyone working in proximity to mechanical air exhaust systems and may be of interest to those providing FM services to commercial buildings. It relates to public and commercial buildings where there may be occasional occupancy by infected persons. Hospital and health care settings are explicitly excluded.

Transmission Routes

Although there are thought to be three transmission routes of the infectious agent, the standard assumption is that transmission via large droplets (droplets or particles emitted when sneezing, coughing, or talking), and via surface contact (surface to hand, hand to face) dominate3,4. A third route has been recognised by the WHO, via fᴂcal matter via droplets caused by flushing WC’s5.

Close Contact Transmission through large droplets (>10 µm)

Droplets are formed from coughing and sneezing and fall onto surfaces, such as desks, tables, or handrails, no further than 1-2m. People then catch the disease by touching the surface and then touching their eyes, nose, or mouth. If people are standing within 1-2 metres of an infected person, they may catch it directly by breathing in droplets sneezed, coughed, or exhaled by them. This is the reason for the 2m separation rule in social distancing. Because of the short travel distance, this is unlikely to be affected by air handling systems.

Airborne transmission through small particles(<5 µm)

Also generated by coughing, sneezing, or talking, these may stay airborne for hours and can be transported long distances. SARS-CoV-2 remains active for up to 3 hours in indoor air and 2-3 days on room surfaces under common indoor conditions6. Therefore small virus particles can travel long distances carried by the airflows in rooms, or the extract air ducts of ventilation systems.

Although there is not yet direct evidence relating to SARS-CoV-2, there is clear evidence relating to SARS-CoV-17,8. There is also no reported data or studies to rule out the possibility of the airborne-particle route, however, Coronavirus SARS-CoV- 2 has been isolated from swabs taken from exhaust vents in rooms occupied by infected patients.

In conclusion, there is clear scientific evidence that mechanical air extract systems can transport virus particulates through the air system and be extracted to air. Hence a virus can be present some distance away from an infected person through such a system, at the air extract point.


REHVA proposes adopting an ALARA principle (As Low As Reasonably Achievable) and to take a set of practical measures to help to control the airborne route.

Recommendations for Building Services Operation

Increase air supply and exhaust ventilation

  • Where a ventilation system is fitted, extended operation times are recommended. Adjust timers to begin ventilation, at normal speed at least 2 hours before, and 2 hours after normal occupancy times.
  • In demand-controlled ventilation systems, lowering the CO2 setpoint to 400ppm to ensure normal speed operation.
  • Keep ventilation on, at reduced speed, in unoccupied buildings.

In short, supply as much outside air as is reasonably possible.

  • Exhaust ventilation in washrooms should be kept on 24/7, making sure that a slight negative pressure is maintained to avoid fᴂcal-oral transmission

Do not change humidification or air-conditioning settings

Coronaviruses are resistant to environmental changes and only extremes, such as RH >80% and temperatures ≥30ºC, have any effect.

Review the type and use of heat-recovery systems

There is a risk that heat recovery devices could carry over the virus attached to particles from the exhaust side to the supply side, via air-leaks.

Regenerative thermal wheels may be susceptible to significant leakage due to poor design or lack of maintenance. The most common fault is that fans are mounted such that a higher pressure is created on the exhaust side, causing leakage into the supply air.

If a leak in the heat recovery system is suspected, pressure adjustment or bypassing is recommended.

Avoid re-circulation sectors in Air Handling Units

Virus particles can re-enter a building when air-handling units are equipped with recirculators. These should be avoided by closing the recirculation dampers, either via BeMS or manually. Whilst this may cause problems with heating or cooling capacity, this must be accepted.

Dampers should be closed even if filters are fitted as standard efficiency filters (F4/F5 or ISO coarse / ePM10 class) will not filter out virus particles.

Some fan coil and induction systems operate with room-level circulation. If possible, it is recommended that these units are turned off as the fan coil units have a coarse filter that will not stop the virus. If they cannot be switched off, it is recommended that they run continuously to prevent the virus from forming a sediment in filters which becomes re-suspended when the fan is turned on.

Duct Cleaning has no effect

Viruses attached to small particles will not deposit easily in ventilation ducts and will normally be carried out by the airflow.9

Changing outdoor air filters is unnecessary

Instances of outdoor virus contamination are rare, and even if air exhausts are close to air intakes, at 80-160 nm, the virus is much smaller than the capture area of normal outdoor air filters (F7 or F84 or ISO ePM2.5 or ePM1)10.

Room air cleansers can be useful in specific situations

To be effective air cleansers need at least HEPA level efficiency. However, because airflow through air cleansers is limited, the area of floor covered effectively is typically <10 m2.

Devices that use electrostatic filtration systems (not the same as portable room ionisers) can be effective, as can specialist UV cleaning equipment.

SSE Actions

SHE Policy

SSE Energy Solutions have adapted its COVID-19 RAMS to acknowledge the potential increase of risk and will now review the ductwork and AHU schematics to understand where exhaust air is extracted from and to. Any form of control measure required to keep operatives safe would be implemented on a case by case basis.

Longer-Term Solutions

Occupant wellbeing is an emerging and future area of interest in the Building Control sector; air quality especially. The UK market has been slow to respond beyond the current functional procurement of ‘standard’ building control solutions whilst air quality solutions, for example, have been adopted more readily elsewhere in the world. This could change in the UK following the COVID-19 pandemic.

We are currently reviewing a number of solutions known to kill flu and other viruses11 that could be installed within air ventilation systems to eradicate the potential to circulate viral infections in buildings managed by control systems.

Summary of practical measures for building services operation by the BeMS Supplier

  • Increase ventilation of spaces with additional outdoor air volumes
  • Switch ventilation to the nominal speed at least 2 hours before the building usage time and switch to lower speed 2 hours after the building usage time
  • At nights and weekends, do not switch ventilation off, but keep systems running at a lower speed
  • Switch air handling units with recirculation to 100% outdoor air
  • Switch fan coils either off or operate so that fans are continuously on
  • Do not change the heating, cooling and possible humidification setpoints

Summary of practical measures for the FM Supplier

  • Ensure regular airing with windows (even in mechanically ventilated buildings)
  • Keep toilet ventilation 24/7 in operation
  • Avoid open windows in toilets to assure the right direction of ventilation
  • Instruct building occupants to flush toilets with closed lid
  • Inspect heat recovery equipment to be sure that leakages are under control
  • Do not plan duct cleaning for this period
  • Replace central outdoor air and extract air filters as usually, according to the maintenance schedule
  • Regular filter replacement and maintenance works shall be performed with common protective measures including respiratory protection

If you would like to implement these recommendations for your building(s) please contact us on 0345 072 9529, or email us at info@sseenergyoptimisation.co.uk


1 https://www.rehva.eu/activities/covid-19-guidance

2 https://www.who.int/docs/default-source/coronaviruse/getting-workplace-ready-for-covid-19.pdf?sfvrsn=359a81e7_6

3 https://www.ncbi.nlm.nih.gov/pubmed/26562748

4 https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0668.2006.00445.x

5 https://www.who.int/publications-detail/water-sanitation-hygiene-and-waste-management-for-covid-19

6 https://www.nejm.org/doi/full/10.1056/NEJMc2004973

7 https://www.ncbi.nlm.nih.gov/pubmed/15737151

8 https://www.ncbi.nlm.nih.gov/pubmed/15737152

9 https://escholarship.org/content/qt2jp9n1rw/qt2jp9n1rw.pdf

10 https://europepmc.org/article/med/4617423

11 These have not yet been tested against SARS-CoV-2