Back to the workplace: safer heating, ventilation and air conditioning (HVAC) systems

By Marc Hill

To support workers who must return to offices and other workplaces while also mitigating COVID-19 spread, building owners, managers and occupiers must assess their spaces and HVAC systems with new challenges in mind. How prepared are buildings to limit the transfer of the COVID-19 virus in working environments?

Building HVAC systems are a key part of the solution for both occupied and partially-occupied buildings.

Where buildings remain vacant, please take a look at our article on managing buildings with reduced usage.

REHVA (the Federation of European Heating, Ventilation and Air Conditioning Associations) has released a guidance document on practical measures that can be applied to HVAC (Heating Ventilation and Air-Conditioning systems). This is intended to work alongside and support the government’s social distancing requirements and advice from NHS England and the World Health Organisation. The recommendations are applicable to support those employees which must travel to work, to limit the risk of infection spread between building users.

First and foremost, despite usual instincts, managers must not simply switch off plant and equipment to save energy during times of reduced usage. Anything we can do to minimise the transfer of infections in the current outbreak is a higher priority than potential energy savings (which would be minimal during the current Spring season in any case).

Research from previous epidemics shows us how viruses similar to COVID-19 can be transferred in small droplets which can in turn be caught in the air movements of ventilation systems. So, supplying as much fresh air as possible and exhausting air to atmosphere can help to remove contaminated particulates from office spaces, before they are inhaled or land on and infect surfaces.

We have outlined 12 practical measures to help prepare building services, per REHVA guidance:

1. Secure ventilation of spaces with outdoor air

Supply air should be provided from outside air wherever possible. If this is not possible, it is recommended that you consider not using these areas.

2. Switch ventilation systems to nominal speed at least 2 hours before the building usage time and switch to lower speed 2 hours after the building usage time

It is not always possible to alter speed dependant on the age of the building. Where it is not possible to change the fan speed, we recommend running at nominal speed 24/7.

3. At nights and weekends, do not switch ventilation off

Keep systems running at lower speed – May not be able to reduce speed, recommend running at full speed where this is not possible.

4. Ensure regular airing with windows (even in mechanically ventilated buildings)

Where buildings have opening windows, it is recommended that these are opened as much as possible, even if this causes some discomfort. (Note: toilets and W/C’s should always have their windows shut).

5. Keep toilet ventilation in operation 24/7

This is to create negative pressure within the toilet areas, as these areas are considered to be of higher risk. (small areas, lots of contact areas, more likely to be sneezing, toilet flushes spread particles as well). COVID-19 has been sampled within stool samples in some studies.

In this higher risk area, avoid open windows to ensure the right direction of ventilation. Building occupants should flush toilets with closed lid to further limit the amount of droplets released into the air.

6. Switch air handling units with re-circulation to 100% outdoor air

Re-circulating air may allow airborne viruses to re-enter the building. The filter media within these systems are generally not able to capture airborne particles with sufficient efficiency.

7. Inspect heat recovery equipment for leakages

This is generally to do with thermal wheels and actuators, which may not “seal” as well as they should, due to wear and tear, or faults. Any leakage may recirculate airborne virus particles as above.

8. Switch fan coils off or operate so that fans are continuously on

This is to avoid spreading the virus around internally, or where necessary keep them running to avoid the virus contaminating the fan coil unit filters and chassis.

9. Do not change heating, cooling and possible humidification set points

There is no evidence that a change in temperature or humidity will impact the proliferation or destruction of the virus. It is noted that relative humidity of 30% or less can increase the likelihood of spreading viral infections.

10. Do not plan duct cleaning for this period

Ductwork cleaning has no theoretical or proven effect on reducing the spread of the virus and could expose the workers to potential infections.

11. Replace central outdoor air and extract air filters according to your maintenance schedule

Please note: the size of the droplets typically expected are unlikely to be caught in conventional filter media installed in an office environment. The types of filters required are generally specialist, for pharmaceutical/laboratory/operating theatres.

12. Regular filter replacement and maintenance works shall be performed with common protective measures including respiratory protection

There’s no evidence that the virus is likely to be completely removed from incoming air by filtration, but it may get caught within the filter media, creating a contamination risk. In addition, filters should be “double bagged” once removed.

Read full CIBSE and REHVA guidance on HVAC systems here: CIBSE guidance, REHVA guidance.

Our highly-experienced building services experts can provide commercial advice in relation to the requirements above to landlords, managing agents, end users and asset, property and facilities managers.

If you would like to discuss the above further, please contact: