Gary Kuzma, practice leader of engineering in Houston, joins Peter Sloan director of interior design in Kansas City, and Vanessa Hostick, sustainable design leader in Kansas City, in examining the role of HVAC systems in controlling the spread of infectious diseases in office space.
Though scientists are still studying how COVID-19 is transmitted, there is a belief that aerosolized particles can spread it. As more research is being done, ASHRAE updated its guidance in April 2021 to state that airborne transmission of COVID-19 is “significant.” In comparison, ASHRAE’s guidance from April 2020 stated that the airborne spread of COVID-19 was “sufficiently likely.”
Many organizations are considering modifications to their buildings’ HVAC systems as part of their plans for bringing staff back into the office after the COVID-19 lockdown. Though there are still questions about the effect of ventilation systems on infections, it’s well known that indoor air quality has a significant impact on people’s physical and mental health—and that employee well-being will be especially critical in the new post-pandemic world.
It’s important to carefully vet all information about the relationship between COVID-19 and HVAC systems. Some can be misleading, and some we’ve seen is just plain wrong. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) is one trusted source that continuously updates its technical information and resources page addressing the impact of COVID-19 on HVAC systems. We also suggest consulting on best practices with a qualified mechanical engineering firm. Depending on a company’s circumstances, connecting with local infection prevention specialists also could be beneficial.
A recent ASHRAE position paper that provides guidance for building owners notes that, when it comes to reducing the spread of the virus, “basic principles of social distancing, surface cleaning and disinfection, handwashing and other strategies of good hygiene are far more important than anything related to the HVAC system.”
That said—and with the possibility that HVAC systems can help contain the spread—there are steps building owners and operators can take to retrofit existing buildings to help reduce bacteria, viruses and other indoor airborne pollutants.
1. Begin by working with building management to determine whether the existing HVAC system is operating as designed.
This requires a commissioning process that assesses the current performance of the building’s HVAC system. Some buildings already have HVAC monitoring systems. Even if they do, however, most aren’t regularly recalibrated to ensure that the data is accurate.
Looking ahead, we can foresee the installation of more advanced building automation systems that evaluate HVAC system performance in real time and even predict corrective measures in advance. As we do for our own annual health checkups, owners and operators will establish long-term relationships with commissioning agents for regular preventative maintenance.
2. Consider increasing the amount of outdoor air to dilute airborne contaminants.
HVAC systems should comply with the outdoor air ventilation rates required by ASHRAE 62.1, which already are considered best practice and are part of many building codes. Increasing the outdoor air ventilation rate beyond this standard—the LEED rating system gives credit for a 30 percent higher rate, for example—can enhance indoor environmental quality (IEQ) and create overall healthier environments.
The building HVAC system must be able to handle the surge in cooling and heating loads associated with a boost in outdoor air. Increasing the outdoor ventilation rate above what a HVAC system is designed to properly de-humidify in humid climates, for example, could cause an unpleasant and undesired increase of humidity in a building.
3. Improve central air filtration.
There’s an ongoing debate about whether air change rates should be increased or decreased to create a healthier office environment. Our recommendation as it relates to addressing COVID-19 is for organizations to stay with their original strategy for air change rates. But they can focus on air quality over quantity by installing more efficient air filters.
Filters with a MERV (Minimum Efficiency Reporting Value) rating of less than 13 do not remove particles in the size range of most viruses that are smaller than 0.3 microns. MERV 13 filters improve filtration efficiency of small particles and are approximately 50 percent efficient for particles from 1.0 micron down to 0.3 microns in size, while MERV 14 filters are 75 to 85 percent efficient in removing these particles and HEPA filters are more than 99 percent efficient. HEPA filters usually are not practical for office applications for reasons related to cost, energy use and operations. Though many newer office buildings already have MERV-13 or MERV-14 filters, older buildings may require more physical space to accommodate them—as well as more powerful air-handling systems to overcome the added air resistance. ASHRAE also recommends sealing filter frames to reduce bypass around the racks and, in some cases, running HVAC systems longer—though 24/7 operations would be costly and may not provide the commensurate benefit.
4. Maintain optimal humidity levels in the space.
Viruses thrive in low-humidity environments. While maintaining 40 to 60 percent relative humidity is ideal for health reasons, keeping it at a minimum of 40 percent is not practical for most office applications. The HVAC systems for most office spaces don’t incorporate humidification. The amount of moisture needed to offset dry outdoor air during the winter and in arid climates largely impacts the cost and decision not to include humidification. Condensation control also has to be considered when outdoor conditions are far different than indoor conditions, which is often the case when outdoor temperatures drop below freezing. The industry standard indoor high limit for most building types is 60 percent relative humidity, which is often achievable without much fuss.
5. Negative pressure rooms prevent the spread of infectious contaminants in medical and research environments, but are not viable solutions for office environments.
Negative room pressure, which controls air flow into a segregated environment, is effective in applications where spaces like labs or hospital isolation rooms are intentionally designed for isolation or containment. But doing this, which requires rooms with physical separation like full-height walls and doors, would be impractical and cost prohibitive for most offices environments.
6. Ultraviolet germicidal irradiation (UVGI) systems installed in HVAC systems can kill airborne particles that carry viruses.
Airstream UVGI is effective for mitigating the transmission of airborne viruses in office and indoor environments. Ultraviolet light devices inactivate a variety of viral, bacterial and fungal organisms. Airstream UVGI can be easily included in retrofit applications. An alternative to airstream UVGI is upper-room UV installations. These use less intense light than airstream UVGI systems designed to kill viruses, carry a higher cost and come with more risk if not properly designed, operated and maintained. Yet they do have the distinct advantage of being able to treat all surfaces in a room exposed to UV light.
7. Virus protection considerations alone should not determine whether office space uses an underfloor or overhead air distribution system.
Both systems have advantages and disadvantages. But neither has a definitive edge when it comes to limiting the spread of the virus. Organizations should opt for the reason they chose a particular air distribution system in the first place.
Consider the Options
Though we don’t expect COVID-19 to result in drastic changes to office building HVAC systems, we do believe there are opportunities for practical but meaningful improvements. As a hallmark of many projects designed for sustainability, enhancements to indoor air quality and thermal comfort are always welcomed by employees.
It’s also true that, more than ever, the perceived “healthiness” of a building will be a market differentiator—whether it’s in attracting the best tenants to a building or the most talented people to a company. Upgraded HVAC systems could play a vital, new role in strengthening people’s feelings of personal security and health in the workplace many will return to in the months ahead.
Related: COVID-19: Design for Change