BSEE
INDUSTRY COMMENT
Engineering healthy workplaces – considerations in response to Covid19
he impact of the Covid-19 lockdown on commercial buildings was immediate – offices emptied overnight as people made the sudden shift to home working. Several months later, and although restrictions are being lifted, an unease about the possibility of localised lockdowns and an uncertainty about the potential health implications of being indoors with larger groups, means fewer people than expected are choosing to go back to office-based working.
T
John Swi, partner and science and technology pracce leader, Buro Happold
Something that might help reassure them that the office is a safe place is knowing that the air they’ll be breathing is clean.
One well-publicised mitigator in the battle against Covid-19 is fresh air. Being outdoors reduces the likelihood of infection and, when indoors, access to adequate ventilation has been highlighted in Government guidance as advisory. As a result, the owners and managers of office buildings are urgently reviewing the measures they need to put in place to reduce the spread of infection and heating, ventilation and air conditioning (HVAC) systems are included within this. As Covid-19 can be transmitted through aerosolization, it needs to be considered through this lens.
As you would expect, Buro Happold has spent a significant amount of time examining how building systems can be augmented to further mitigate the spread of airborne infections like Covid-19. While some new technologies show promise in helping to address the issue, there are also practices from other sectors that can be drawn on and implemented in commercial workplaces.
Air filtration
Looking first to hospitals for best practices to draw on, increasing the level of filtration within a HVAC system is a relatively simple way to improve its ability to trap airborne pathogens. Although hospital grade filtration may not be necessary for a standard office environment, increased filtration will undoubtedly aid the fight against air borne pathogens.
The Minimum Efficiency Reporting Value (MERV) is a scale from 1-20 that defines the ability of a filter to trap particles: the higher the MERV rating, the more particles a filter can capture. Although standards such as LEED, WELL and other green building rating systems require HVAC systems to
8 BUILDING SERVICES & ENVIRONMENTAL ENGINEER SEPTEMBER 2020
use filters that meet at least a MERV 13 rating, at Buro Happold, we prefer to specify electronic filter technology with a MERV 15 rating. This higher rating results in a system that can filter viruses and bacteria more effectively and at a lower pressure drop than standard MERV 13 filter systems.
Air exchange rate
Another factor that impacts the spread of airborne contaminants is the air exchange rate of the building - the fewer air changes, the more likely it is that contaminants remain in a building. This is an area where office building owners could look to the broader healthcare sector for best practice to draw on.
Healthcare environments, driven by a requirement for sterile and ultra-hygienic atmospheres, have long practiced high air change rates, finding the optimal rate in critical areas such as operating theatres to be greater than 20 air changes per hour. Although commercial businesses do not need to provide as high a level of infection control, increasing air changes beyond the recommended minimum ventilation rates could be very beneficial for the health of office workers. As an aside, studies also show that buildings with higher air change rates benefit occupant health by improving cognitive function and therefore increasing productivity levels.
In order to exhaust more air through methods beyond increasing air change rates throughout the day, building owners should also consider leaving HVAC systems active for a set time after workers have left for the day to flush out contaminated air before they return the next morning. It is important to note, however, that the benefits of increased ventilation have to be balanced with the increase in energy consumption they generate.
Air quality monitoring
The third practice that jumps out as being relatively quick and easy to implement – and that could provide reassurance for office workers - is improved air quality monitoring. Third party human health and sustainability certification standards (such as LEED, WELL, Living Building Challenge, and Reset) are increasingly requiring performance-based air quality results through one-time, annual, or continuous air quality testing.
Advances in technology have drastically reduced the cost of sensors and they can now operate as stand-alone monitors or integrate with Building Management Systems (BMS). Sensors can be used to measure a variety of indoor air quality metrics, including CO2, total volatile organic compounds (TVOCs), humidity, temperature, and particulate matter. Importantly in times like these, sensor data can be viewed remotely and can be integrated with wider monitoring practices to troubleshoot building health issues as well as energy demand concerns.
Air treatment
Technologies such as Ultraviolet C (UVC) lighting is used for the disinfection of surfaces and spaces in many industries and is a methodology that could relatively easily be incorporated into commercial HVAC designs. Low-level far-UVC light is being studied for its potential to limit airborne pathogens. Preliminary research from Columbia University’s Center for Radiological Research shows that this form of UVC can effectively inactivate >95 per cent of aerosolised influenza viruses. Simultaneously, this research has found that the far-UVC cannot penetrate the outer layer of mammalian skin, establishing the potential for low-level far-UVC light to be used overhead in many public spaces. Bi-polar ionization is another technology that appears to be effective in limiting airborne pathogens. Although more research is needed to study the efficacy of these technologies when integrated into HVAC air systems, there is evidence that they can effectively inactivate Covid-19.
In addition to the practices set out above – which are fairly straight forward to implement - there are other system enhancements, such as, humidification control or the pressurisation of spaces from clean to less clean, that could also be considered on a case-by-case basis. The ASHRAE Position Document on Infectious Aerosols provides comprehensive technical guidance on these issues.
Covid-19 has pushed the issue of airborne sickness transmission through HVAC systems into the spotlight. In response, engineers are considering new design guidelines that incorporate methods to mitigate the spread of airborne pathogens and we continue to research new technologies and industry practices to optimise the air quality in our workplaces.
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