Article By: Kevin Sharples (B.A.Sc., P.Eng.), Kurt Monteiro (B.A.Sc., P.Eng., LEED AP, HFDP, HBDP), Douglas Smith (BA.Sc., P.Eng.), Dan Larson (B.A.Sc., P.Eng., Eng. / ing., LEED AP BD+C), Andrew Caller (B.Eng., P.Eng., LEED AP), Greg Trypuc (P.Eng., LEED AP), Tony Spina (C.E.T.)
Life was very different four months ago. Practices like “social distancing”, “self isolation”, and “community spread” were not considered mainstream in January. In the wake of COVID-19, concern about the invisible is now visible on the face of every participant in every virtual meeting that (seemingly overnight) has become the norm.
Invisible threats—airborne pathogens like viruses and bacteria—have always been a central consideration in each of our mechanical designs. Limiting the spread of airborne pathogens plays a big role regardless of the building type and, in many spaces (such as healthcare and laboratory facilities) this is actually a design driver. Technology regularly leveraged in such spaces is now up for discussion in every building type—hotels, office buildings, restaurants, shopping centres—as building managers, operators, and developers examine every possibility in the context of opening up shared spaces in a safe and healthy way.
There is no conclusive, peer-reviewed research that confirms that SARS-CoV-2 is distributed by the HVAC system and, based on current infection patterns, the HVAC system is likely not a high transmission pathway for SARS-CoV-2. However, research is ongoing, and the solutions under consideration (some of which are outlined here) have demonstrated efficacy for other airborne pathogens.
Based on the research available to date, the most significant threat surrounding contracting COVID-19 is presented through direct contamination within the workplace and not airborne concerns. Insufficient social (physical) distancing, contact with contaminated surfaces, and subsequent contact with the hands, eyes, nose, and mouth are the more prevalent concerns in shared spaces during this pandemic. That being said, HVAC design is always evolving, and never more so than after a global pandemic. We must review the technology available with an open mind and a level head. A closer examination of preventative measures for this specific health concern may result in design and operations practices that further support overall wellness in indoor environments.
Before any decisions are made, a thorough understanding of the building systems involved, and the risks and benefits each part provides in the indoor air environment, is required. An under floor air distribution (UFAD) system circulates air differently than displacement ventilation or overhead air distribution. Airflow in partially or naturally ventilated buildings is variable and unpredictable, so the ability to actively manage the spread of airborne pathogens in buildings that implement these systems is not straightforward.
There is conclusive research demonstrating the direct relationship between the number of airborne particles and the rate of transmission among airborne pathogens. Most large particles in the air stream drop to the ground within two metres of where they were expelled—dropping outside of the “breathing zone”. Medium-sized particles move through spaces and HVAC systems, and are captured by the appropriate filters. Smaller particles—particles that can support the transfer of a virus like SARS-CoV-2—largely stay suspended in indoor spaces, and are not impacted by HVAC system air currents. It is, therefore, less likely that these particles would be captured by conventional HVAC media filters.
Drawing from our experience with healthcare design across the country, some possible design solutions that may help limit the spread of airborne pathogens include:
Without a cure or a vaccine for COVID-19, it is tempting for many to want to point to a single solution for the answer. But, if there’s one thing that 55 years of HVAC design has taught us, it’s that there is no “one size fits all” solution. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) released a Position Document on Infectious Aerosols (Approved by ASHRAE Board of Directors on April 14, 2020). In this document, ASHRAE emphasizes that mitigating infectious aerosol dissemination should be a consideration in the design of all facilities, yet reminds that:
“The design and operation of HVAC systems can affect infectious aerosol transport, but they are only one part of an infection control bundle.” (ASHRAE Position Document on Infectious Aerosols, April 14, 2020)
We need to rely on one another’s strengths, balance innovation and skepticism, and work together to clear the air.
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Editor's Note: This article was originally published on May 13, 2020. As of June 9, 2020, research on the airborne nature of SARS-CoV-2 remains ongoing, with an increased amount of research conducted within a healthcare setting indicating the likelihood of airborne transmission. Much of this research remains inconclusive, though precautions are encouraged. Smith + Andersen continues to review available technology and provide our clients with appropriate solutions in conjunction with the latest research and technology available.