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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
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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
ADF OCTOBER 2021
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