Ventilation: The key to infection control in commercial properties?

As businesses look to get people back into buildings and workplaces in the wake of the pandemic, there is a very clear need to ensure that action is taken to make buildings safe for re-entry. There has been much focus on social distancing, sanitisation, and PPE, but one area which has moved rapidly up the agenda is how to manage the operation of ventilation systems in commercial properties. This is in the context of mitigating the spread of COVID-19, should someone entering the building have the virus, and the implications this brings in terms of energy use.

In the traditional infection control hierarchy, management of ventilation systems to mitigate the spread of a pathogen falls under ‘engineering controls’. Engineering controls rank higher in effectiveness than both instructing people what to do / how to behave (administrative controls) and the use of Personal Protective Equipment (PPE). The premise is that eliminating the virus, or at least operating the systems to separate people from the virus, is more effective than allowing it to be present but instructing people to, for example, maintain their distance and use PPE (see figure 1). The importance of managing the ventilation systems in a building in such a way to help mitigate the spread of the virus should therefore not be underplayed, given the growing body of research around airborne transmission.

As stated by the Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA):

“New evidence on SARS-CoV-2 airborne transmission and general recognition of long-range aerosol-based transmission have developed recently. This has made ventilation measures the most important engineering controls in the infection control. While physical distancing is important to avoid a close contact, the risk of an aerosol concentration and cross-infection from 1.5 m onward from an infected person can be reduced with adequate ventilation and effective air distribution solutions.”

Whilst the over-arching message from the industry is to maximise the provision of outside air into the building, there are a number of important factors to consider in the guidance including the following:

• Maximise outside air provision (supply air) from mechanical ventilation systems by increasing air supply and operating times.
• Use windows to increase ventilation in naturally ventilated buildings, as well as to boost air rates in buildings with mechanical ventilation systems.
• Seek specialist advice on air-conditioning systems utilising central air-handling plant with a mixture of recirculated and outdoor air. Centralised recirculation systems of this type (the most common of which is Variable Air Volume or VAV) should not generally remain in use without specialist consideration.
• Assess cross contamination risks in heat recovery systems between exhaust air and outside / supply air and take appropriate action. For example, thermal wheels are an inherent risk because it is physically impossible to make an air-tight seal between the two air streams.
• For toilets, keep mechanical ventilation (extract) in operation 24/7 with relative negative pressure created, avoiding windows being left open to ensure the right direction of ventilation.
• In most cases, if it is not practical for fan coil units to be turned off, the fans should operate continuously, 24/7.

The industry guidance which has been developed to support this, whilst detailed, must be applied appropriately in line with the specific systems installed within each building. Additional challenges which mean building management teams must give this due time and attention include:

• Guidance in this area is rapidly advancing and changing as research progresses so this must be kept on top of and changes to strategies made as appropriate.
• Limitations to application of the guidance exist in some instances. These need to be understood so building managers can demonstrate that the best possible action has been taken, within the limitations presented. In some cases, additional changes may need to be considered to overcome limitations where risks are evident.
• Application of the guidance could in many buildings significantly increase energy use. Where buildings are occupied, the first priority will be to ensure that systems are being operated safely in line with the guidance, but building management teams will need to quickly review the potential energy penalty that this brings about and work to identify solutions to mitigate this. Whilst the impacts of the pandemic have been disruptive and destructive, so too are those threatened by the Climate Crisis so the energy element cannot be neglected. It is also important to minimise costs and protect budgets at this difficult time as far as possible.
• The practicalities of different summer and winter requirements need to be understood, and how this impacts the ventilation strategy as we move from summer to winter in the coming months. A proactive approach by reviewing this early on will allow due consideration to the impact on energy and potential steps which can be taken to mitigate increases.

If site specific reviews of the operation of your ventilation systems have not yet been undertaken we recommend the following actions are taken:

• Prioritise a review of the ventilation systems for any occupied sites and ensure immediate action is taken to increase ventilation and mitigate the risk of spread of the virus.
• Next, understand the implications of any changes made on energy use within those buildings and investigate what steps can be taken to reduce the energy as far as possible, whilst maintaining safe operation of systems. In some cases, this may require changes to be made to the configuration of the Building Management System (BMS).
• For sites which have not yet returned to occupancy, ensure a detailed evaluation of the ventilation systems is undertaken early on to feed into your building re-entry strategy. This will ensure steps can be taken proactively when occupiers return to run the systems safely, whilst also minimising energy use.
• Even where the energy implications of these changes to the operation of building services is well managed, this is still likely to result in some increase in energy use. Now more than ever is the time to look more widely at opportunities across buildings for saving energy and to take action to both offset these potential increases, and go beyond as we look to ‘Build Back Better’.

Further detail on building and workplace re-entry can be found in the Carbonxgen guide ‘The Road to Recovery and Sustainable Resilience: Part 1’ available to download here: https://www.carbonxgen.com/portfolio/building-and-workplace-re-entry-pt1/