Considerations for office ventilation design in a post-Covid world by cundallglobal

Considerations for office ventilation design in a post-Covid world APRIL 2021

Document purpose This document outlines current thinking on ventilation considerations that alter existing design guidance for new and refurbished offices and fitout of workplaces as well as guidance on effective operation of existing workplaces as we return to office occupation following the Covid-19 outbreak. It covers UK & international guidance. The science behind this is likely to be applicable in other sectors and regions. The guidance is an initial design note for discussion, with individual project and occupant needs balanced against legislative requirements such as energy efficiency. Where possible, we try to be objective about the relative merits of different technologies and approaches on the market, and the magnitude of likely benefit they bring for additional cost or energy consumption.

Considerations for office ventilation design in a post-Covid world

Overarching considerations “Indoor ventilation is part of a comprehensive package of prevention and control measures that can limit the spread of certain respiratory viral diseases, including COVID-19. However, ventilation alone, even when correctly implemented, is insufficient to provide an adequate level of protection. Correct use of masks, hand hygiene, physical distancing, respiratory etiquette, testing, contact tracing, quarantine, isolation and other IPC measures are critical to prevent transmission of SARS-CoV-2” [1]

Any ventilation measures proposed therefore need to be considered within the wider context of building operation, health impact on occupants, and value for money considered.

Considerations for office ventilation design in a post-Covid world

Existing guidance for ventilation during COVID-19 A number of guides have been produced to propose suitable management and ventilation measures. At the time of writing, these include, but are not limited to: The World Health Organisation (WHO) Roadmap to improve and ensure good indoor ventilation in the context of COVID-19 – The WHO have prepared a simple roadmap summarising measures to reduce risk for naturally and mechanically ventilated buildings, including domestic, non-domestic and healthcare settings. Scientific Advisory Group for Emergencies (SAGE) EMG – Simple summary of ventilation actions to mitigate the risk of COVID-19 – SAGE EMG provide detailed, peer reviewed scientific guidance from health and ventilation experts. The Health and Safety Executive (HSE) – Ventilation and air conditioning during the coronavirus (COVID-19) pandemic – The HSE has prepared a thorough, easily understood, guide for assessing all aspects of ventilation in the workplace. This should be followed when preparing a risk assessment for return to work.

Federation of European Heating, Ventilation and AC Associations (REHVA) Covid Guidance – REHVA have produced comprehensive guidance, and a number of tools covering all aspects of ventilation. Their FAQ section is particularly useful. Chartered Institution of Building Services Engineers (CIBSE) – Emerging from lockdown - CIBSE have produced guidance similar to that produced by REHVA but focused on the UK market. A guide to the specification of air cleaners is due to be released shortly.

Considerations for office ventilation design in a post-Covid world

ASHRAE - Epidemic Task force guidance – ASHRAE have prepared a wealth of guidance accessed from this infographic. Their summary of ventilation and filtration technology is especially thorough. British Council for Offices (BCO) - Thoughts on Ventilation Design and Operation Post Covid-19 – The BCO Technical Committee have summarised the REHVA guidance for a non-technical commercial office audience, with some suggestions around their own BCO standards for ventilation post COVID-19.

FAQs Are standalone or in-duct air cleaners an effective solution? There are a variety of ‘alternative’ or novel technologies currently being marketed for removal or deactivation of SARS-CoV-2 from the air. A SAGE review of the scientific research associated with alternative devices, concluded that, “Other technologies (ionisers, plasma, chemical oxidation, photocatalytic oxidation, electrostatic precipitation) may generate undesirable secondary chemical products that could lead to health effects such as respiratory or skin irritation (medium confidence). These devices are therefore not recommended unless their safety and efficacy can be unequivocally and scientifically demonstrated by relevant test data.” (SAGE-EMG, Nov 2020 [7]). The scientific evidence suggests that fibrous filtration (e.g. HEPA) and to a lesser extent UV based technologies could be part of the solution in minimising risks where there is insufficient outside air supply. The World Health Organisation states: “If no other (short-term) strategy can be adopted, consider using a standalone air cleaner with HEPA filters.” CIBSE and REHVA both recommend UV-C as a possible alternative to HEPA, though is unlikely to be a ‘plug and play’ solution, particularly in existing buildings. In all cases guidance on safe use should be followed.

The effectiveness of in-duct UV is a function of lamp output (the higher the better) and air velocity (the lower the better). In most non-healthcare settings air velocity is high, which means long runs of lamps or higher output lamps will be required. This likely makes it impractical to install an effective system in most buildings. Short runs of UV lamps designed to treat a cooling coil, for example may cause a slight reduction in airborne viral load, but it is unlikely to be significant due to the short dwell time. Upper room UVGI, which involves installing UV lamps at high level to irradiate the air above the occupied zone is known to be effective, as it treats a large volume of air all at once, but is unlikely to be suitable outside of a healthcare setting due to the potential health risks of accidental UV exposure and difficulty retrofitting. Standalone air cleaners are only likely to have a short range of effectiveness – as the fans within the devices can only entrain a relatively small amount of air. CIBSE is releasing guidance shortly on the selection of in room devices. In general, they should be placed close to the likely source of infection (e.g. in a clinical setting) or in the centre of the room if there is no known source. Make use of the clean air delivery rate (CADR) if available.

Is there a system design which reduces viral transmission risk? The main issues to consider in system selection and design are: 1. Is it designed to provide enough outside air? 2. Does the ventilation system distribute and mix the air well? 3. Does the ventilation system encourage movement of air from potential sources of infection out of the breathing zone? E.g. through displacement. REHVA guidance states, “a fully mixing air distribution system, capable of completely mixing contamination from a point source in a large room in one hand, and vertical stratification and exhausts capable of removing the higher concentration before it is completely mixed, would be beneficial.” This suggests that a well-designed displacement ventilation system, capable of simultaneously diluting and removing pathogens, would likely be most effective in reducing risk. Incorporating free cooling with outside air when conditions allow, would provide further air quality benefits, and further supports the use of a high-volume displacement type system. For all systems, the COVID-19 pandemic has shown the benefit of openable windows. Not only do they enable building users to supplement mechanical systems, if designed correctly as part of a mixed-mode system, they also form a key part of the drive towards net zero. As such, openable windows should be provided wherever possible. CIBSE AM10 provides guidance on window design.

Considerations for office ventilation design in a post-Covid world

Will fitting HEPA or high efficiency filters into the existing system provide “clean air”? HEPA filters are typically used in medical applications, and filter 99.97% of particles of 0.3μm. “The peak concentration of SARS-CoV-2 aerosols appears in two distinct size ranges, … with aerodynamic diameter dominant between 0.25 to 1.0μm, and…with diameter larger than 2.5μm” [3]. Therefore, filters applicable to this range (M6 and better) are likely to reduce airborne viral load. In the case of HEPA filters, the high pressure-drop associated with the filter, and the likelihood that systems will need new filter racks to allow sufficient sealing to prevent filter bypass mean retrofit is not usually feasible in existing systems. For lower grade filters such as F7 (MERV13), an assessment of the system should be made to determine the impact on energy consumption and air flow. ASHRAE have outlined a detailed method to do that, here.

ASHRAE 52.2

Filters upgrades in AHUs Systems which supply only air directly from outside (with no recirculation) such as the AHU in typical Fan Coil Unit (FCU) systems do not require any changes to filtration, as there is a low risk of SARS-CoV-2 aerosols from outside outdoor air quality should determine filter specification, as normal. Filter upgrades in FCUs Upgrading filters on FCUs to F7 (MERV13) is impractical due to the pressure drop they induce, and even if possible, will likely lead to specific fan powers (SFPs) which exceed UK building regulations, increase operational energy consumption, and make net-zero targets harder to achieve. If there is sufficient outside air being provided to a room, FCUs will help mix the air, reducing stagnation. If there is insufficient fresh air, they should be turned off, as they can increase the risk of viral spread.

EN779

ISO ePM1

ISO ePM2.5

ISO ePM10

ISO Course

MERV 5

>80%

MERV 6-7

>90%

MERV 8-9

>50%

MERV 10-12

50-65%

>60%

MERV 13

50-65%

65-80%

>85%

MERV 14

65-80%

>80%

>90%

MERV 15

>80%

>95%

Considerations for office ventilation design in a post-Covid world

How can I tell if my office has sufficient outside air? Sufficient ‘fresh’ outside air has been defined by most guidance as a minimum of 10l/s.person. This can be determined through a thorough review of record drawings for the building, ideally with recent commissioning data which confirms the distribution to different zones and rooms across each floorplate. If this data is not available, Non-dispersive Infrared (NDIR) CO2 sensors can provide an indication of insufficient ventilation. Sensors should be provided in occupied zones, ideally in the breathing zone (1.2-1.8m from the floor) and away from windows, diffusers, and grilles.

Post-Covid / [Pandemic-mode]

Pre-Covid

References

Occupancy (l/s∙person)

Area Rate (l/s∙m2)

Occupancy (l/s∙person)

Area Rate (l/ s∙m2)

Building Regulations

10 [15]*

CIBSE

10 [>10]

CIBSE Guide A

BCO

13.2

14 [>14]***

BCO - Thoughts on Ventilation Design and Operation Post Covid-19

ASHRAE

8.5**

8.5 [>8.5]

Part F Consultation

ASHRAE 62.12016

*value taken from the Future Buildings Consultation version – use whichever is greater – area or occupancy rate **at default occupancy rate – other factors apply – see reference ***The BCO are recommending that CO2 levels are kept below 1000ppm in shared transient spaces such as stairwells and lobbies

How much air should I provide for a new office? A number of organisations have amended their recommendations for fresh air provision to office spaces following the pandemic. A number of sources are suggesting either a permanent increase in ventilation rates (BCO) [2] or the potential for increased ventilation to be designed in for pandemic scenarios (Future Buildings Consultation – Part F). In a pandemic scenario, research suggests that increased ventilation reduces infection risk, and should be encouraged. There is little evidence to suggest that maintaining a higher rate of fresh air rate than 10l/s∙person is necessary to maintain good air quality in a non-pandemic scenario. The new version of Part F is suggesting that fresh air is provided on a floor area rate to non-occupied spaces such as stairwells, which seems a sensible, balanced approach.

The minimum recommended amount of air is 10l/s∙person (WHO/ CIBSE/REHVA). This applies to both natural and mechanically ventilated spaces. It is our opinion that the existing recommendations for fresh air volumes should be followed in future office design. In a pandemic situation, it is likely that many staff will be forced to work from home. As a result, the increased (pandemicmode) fresh air volume is likely to be met through lower occupancy.

Is there an impact on energy efficiency of the above increases in ventilation rates? The majority of guidelines are maintaining their pre-Covid rates. The BCO have slightly increased their minimum recommended fresh air volume to meet a default recommendation in a little used EN ISO standard. If occupancy rates return to normal this will likely lead to an increase in fan, and heating and cooling energy in existing buildings, and an increase in duct and riser sizes, and heating and cooling energy in new buildings unless implemented alongside a demand control strategy, using CO2 control to reduce outside air supply. The consultation version of building regulations is suggesting that capacity for an extra 5l/s∙person is designed into office ventilation systems, though no guidance is given on how this should operate, or whether it could be provided by openable windows for example. This may not make the final version of Part F. It is likely that in a pandemic scenario many people will return to working from home and the higher per person rates will be met as a result of lower occupancy. As a result, at the time of writing, we do not recommend increasing the designed minimum fresh air supplied unless required by future building regulations.

Considerations for office ventilation design in a post-Covid world

Should I turn off systems with local recirculation? If there is sufficient outside air (at least 10l/s∙person), local recirculation systems, such as fan coil units or ‘splits’, can help mix the air in the room, reducing stagnation and improving dilution. Recirculation in central air systems CIBSE recommend avoiding recirculation in central systems unless it is specifically required to maintain adequate levels of outside air. Any new buildings which propose a recirculating primary fresh air system should include a full fresh air bypass.

Heat Recovery Well designed and installed thermal wheels present a low risk but they do have potential for cross contamination if poorly maintained or operated. The use of thermal wheels may be necessary to maintain a sufficient supply of outside air in existing buildings. The REHVA COVID 19 guidance has a comprehensive section on assessment of existing thermal wheels, and correct design to ensure leakage is minimised. Run around coils or plate heat exchangers have negligible or zero risk.

Considerations for office ventilation design in a post-Covid world

Should I use IAQ monitors?

In the absence of historical design information, Non-dispersive Infrared (NDIR) CO2 monitors can provide useful information on ventilation effectiveness, and rates of dilution based on occupancy, as such, they are best used in cases where the system performance is unknown. They can also be used to assess the distribution of air in large spaces, and correct operation of systems. Note that most electronic CO2 monitors are sensitive to local airflow, so they should be located close, but not too close to occupants, and ideally within the breathing zone.

References WHO, “World Health Organization. (>2021)>. Roadmap to improve and ensure good indoor ventilation in the context of COVID-19,” 26 2 2021. [Online]. Available: https://apps. who.int/iris/handle/10665/339857. [Accessed 01 3 2021]. [1]

B. C. f. O. TAC, “Thought on Ventilation Design post COVID-19,” BCO, 24 2 2021. [Online]. Available: https:// www.bco.org.uk/Research/Publications/Thoughts_on_ Ventilation_Design_and_Operation_Post_Covid-19.aspx. [Accessed 15 3 2021]. [2]

Z. N. Y. C. M. G. Y. L. N. K. G. L. S. Y. D. J. C. D. W. X. L. K.-f. H. H. K. Q. F. K. L. Yuan Liu, “Aerodynamic Characteristics and RNA Concentration of SARS-CoV-2 Aerosol in Wuhan Hospitals during COVID-19 Outbreak,” bioRxiv (pre-print), 2020. [3]

CIBSE, “CIBSE COVID-19 Ventilation Guidance,” 2020. [Online]. Available: https://go.cibse.org/l/698403/202010-24/3bvyrx/698403/1603540438B53rOzcU/Covid_19_ Ventilation_guidance_v4.pdf. [4]

SAGE-EMG, “Potential application of air cleaning devices and personal decontamination to manage transmission of COVID-19,” 19 11 2020. [Online]. Available: https://www.gov.uk/government/publications/emgpotential-application-of-air-cleaning-devices-and-personaldecontamination-to-manage-transmission-of-covid-19-4november-2020. [Accessed 03 03 2021]. [8]

REHVA, “REHVA COVID 19 Guidance,” 2020. [Online]. Available: https://www.rehva.eu/fileadmin/user_upload/ REHVA_COVID-19_guidance_document_V4_09122020. pdf. [9]

ASHRAE, “ASHRAE Epidemic Task Force COVID-19 Infographic,” 2021. [Online]. Available: https://www.ashrae. org/file%20library/technical%20resources/covid-19/ ashrae-covid19-infographic-.pdf. [Accessed 17 03 2021]. [10]

HSE, “Ventilation and air conditioning during the coronavirus (COVID-19) pandemic,” 1 3 2021. [Online]. Available: https://www.hse.gov.uk/coronavirus/equipmentand-machinery/air-conditioning-and-ventilation/index.htm. [Accessed 3 3 2021]. [5]

SAGE-EMG, “EMG: Simple summary of ventilation actions to mitigate the risk of COVID-19, 1 October 2020,” 01 10 2020. [Online]. Available: https://assets.publishing. service.gov.uk/government/uploads/system/uploads/ attachment_data/file/945754/S0973_Ventilation_Actions_ Summary_16122020_V2.pdf. [Accessed 03 03 2021]. [6]

SAGE-EMG, “Mitigations to Reduce Transmission of the new variant SARS-CoV-2 virus,” 23 12 2020. [Online]. Available: https://assets.publishing.service.gov.uk/ government/uploads/system/uploads/attachment_data/ file/948607/s0995-mitigations-to-reduce-transmission-ofthe-new-variant.pdf. [Accessed 03 03 2021]. [7]

Considerations for office ventilation design in a post-Covid world

Author:

Sector lead contacts:

Edwin Wealend Head of Research and Innovation CIBSE Air Quality Group Chair

Kevin Hayes Partner Buildings services

e.wealend@cundall.com +442074381750

k.hayes@cundall.com +442074381667 Michael Gosling Associate Director Building services m.gosling@cundall.com +441217943503

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