View Point: Hywel Davies of CIBSE

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With Covid-19 sadly not likely to disappear any time soon, achieving the correct ventilation of workplaces is critical to mitigate the spread in future. Hywel Davies of CIBSE discusses the issues for designers

Covid-19 is not going away any time soon. Immunologists, infectious disease researchers and virologists expect the virus to circulate and evolve in the global population for years to come – much like influenza and the four endemic human coronaviruses that cause common colds.

For those involved in the design of new buildings and the modification and refurbishment of existing buildings, the continued presence of coronavirus makes it essential that offices and public buildings are designed with effective ventilation to create a safe working environment.

Ventilation is needed to combat infection because there is a growing body of evidence that appears to show that the SARS-CoV-2, the virus that causes Covid-19, can be spread by very small particles (aerosols) in a similar way to that of cold and flu viruses.

Aerosols – alongside larger droplets – are released by an infected person when they cough, sneeze, talk and breathe. The larger droplets fall to the ground within 2 metres of the source, which is why social distancing is recommended. Smaller aerosols can stay airborne for hours, which enables them to travel longer distances where they can infect secondary hosts.

In a well-ventilated room, air supplied to the space will help dilute the concentration of aerosols, while extracting air will assist in the removal of airborne pathogens to outside – helping reduce the possibility of inhalation by room users and their deposition on indoor surfaces.

The provision of good ventilation has other benefits; bringing a stream of outside air into a space and removing stale air helps create a healthy indoor environment for occupants. In addition to reducing levels of illness, this will also help improve concentration levels, and increase productivity.

By contrast, in rooms that are poorly ventilated, the concentration of aerosols and airborne pathogens will inevitably be higher, putting occupants at risk of infection; a risk that will increase in line with the amount of time spent in the space.

When it comes to the design of new buildings, the Building Regulations require that an adequate means of ventilation be provided in a building. In England, ‘Approved Document F: Ventilation’ sets out what is considered, in ordinary circumstances, to be adequate ventilation, while in the devolved nations there are alternative regulations and guidance in place.

The minimum ventilation rates required by the current Building Regulations should be effective in helping prevent the spread of Covid-19, where the ventilation system has been designed by a competent engineer and installed appropriately.

However, we recommend that systems be designed to enable outside air flow rates to be increased above the minimum needed for compliance, to further limit the possibility of airborne transmission of Covid-19 – wherever it is reasonable to do so – without causing discomfort or a significant increase in energy demand. Also, that the ventilation system should not recirculate air from one space to another.

The recommendation that systems are designed to enable increased outside air flow rates is reflected in the recent consultation on proposed changes to Approved Document F. This includes a requirement that office ventilation systems are designed “to have the means to increase the general ventilation rate of each occupiable room by 50% so that it can operate for long periods (e.g. months) at a higher ventilation rate,” to help reduce the spread of airborne infection in those periods when airborne infections are prevalent.

Regardless of whether the proposed changes to Part F are implemented, it seems inevitable that ventilation systems will need to be designed with the ability to enhance ventilation rates to help create a safe working environment in the current pandemic, and for future pandemics.

Engineering systems for increased ventilation will inevitably have an impact on building design. For mechanically ventilated buildings, it may well be that the ventilation systems have to increase in size if they are to circulate higher volumes of air for longer periods of time without unduly increasing energy consumption and noise levels. That could mean larger distribution ducts and a corresponding increase in plant space. Early involvement of building services engineers will help develop designs that provide effective ventilation – keeping costs to a minimum and ensuring careful co-ordination and integration with the structure and interior design.

The provision of effective ventilation is not simply about increasing the volume of air blown into, and sucked out of, spaces, it is also about ensuring the effective distribution of air within spaces. That requires the supply and extract to be positioned precisely to ensure air can move unobstructed through a space and stagnant air pockets are eliminated (where aerosol concentrations could be higher).

For naturally ventilated buildings, where a space is reliant on opening windows and doors for ventilation, the general advice is that the scheme should be designed on the assumption that windows and vents will be used more than normal when airborne infection rates are high.

When refurbishing or redeveloping existing buildings, the provision of good ventilation can be more of a challenge. Where a building’s ventilation system is being replaced, this should be relatively straightforward. However, where an existing ventilation system is being considered for upgrade or improvement to increase clean air delivery, developers and designers need to be mindful of the possibility of unintended consequences.

The continued presence of coronavirus means that effective ventilation will continue to be a critical factor in the design of workplaces. Unlike social distancing and hand washing, ventilation requirements are not easily distilled into one simple approach that everyone can follow. Assessing ventilation needs across a range of environments can be challenging and often requires engineering expertise to ensure any proposed scheme or mitigation measures will be effective for a particular building type, ventilation system, user group and activity.

Two new guidance documents on reducing Covid-19 transmission through ventilation and air cleaning technologies have been published by the Chartered Institution of Building Services Engineers (CIBSE). The guidance is available to download for free from the ‘Coronavirus Advice’ section of the CIBSE website www.cibse.org

Hywel Davies is technical director of the Chartered Institution of Building Services Engineers