A Conversation with ASHRAE President Chuck Gulledge
Southern PHC Magazine spoke with Chuck Gulledge recently to get his views on near-term and long-term actions the HVAC industry should be considering in regards to the COVID-19 pandemic.
Regarding IAQ as it relates to airborne pathogens, what near-term strategies should the industry embrace? Should we take a wait-and-see approach or are there proactive measures that can be taken today that will yield benefits to building owners and occupants?
The pandemic has magnified awareness of human health within the built environment; in particular, infection control in non-healthcare buildings. It is fair to say that a wellness, or a concern for personal health, mindset has quickly developed for building occupants. We understand that airborne risk is likely higher in any indoor environment compared to being outdoors.
Near-term strategies that our holistic HVAC ecosystem should embrace follow the classic “Hierarchy of Controls” related to minimizing and/or eliminating exposure to a hazard. The most effective response is physical removal of the hazard (Elimination); which we do not control. This is followed by attempts to replace the hazard (Substitution); unfortunately, we cannot substitute one pathogen for another in this case.
Engineering Control strategies offer immediate assistance in minimizing exposure via efforts to mitigate transmission of the hazard. Effective ventilation, filtration, pressurization, distribution, disinfection, and temperature/humidity control can all be leveraged to reduce the risk of aerosol and airborne transmission exposure related to bioburden.
“Given that COVID-19 is transmitted via contaminated air, it is clear that measures applied to HVAC systems may reduce risk of infection. The HVAC system is an asset that can help mitigate the transmission of this virus.”
Administrative Controls focus on the dynamic of people interaction. As humans generate and transmit the virus, it is imperative to understand the dynamics associated with individual transmission opportunity. The virus typically resides in respiratory droplets and droplet nuclei. Individuals should be separated to mitigate exposure from aerosol and large droplet spray via distance, traffic patterns, and occupancy levels.
Finally, individual protection can be exercised via use of Personal Protective Equipment (PPE). Well-fitted, high efficiency (e.g., N95) masks can protect the wearer from local transmission of contaminant. N95 masks that have exhaust vents protect the wearer, but not those around them. The exhaust vent still allows aerosols from the wearer to escape into the space around them.
Clothe masks do not necessarily qualify as highly effective PPE, although they do reduce the amount of inhaled infectious aerosol. More importantly, they function as a “personal engineering control” that alters the emission characteristics from the source.
Engineering controls, administrative controls, and PPE can, and should, all be embraced now. Wait-and-see is not a prudent approach. Collectively, these controls provide our best mitigation response to this pandemic.
What are the long-term strategies we, as an industry, should be contemplating? What do you think manufacturers should be thinking about in terms of system design? How should contractors advise their customers in planning long-range about their HVAC systems?
Ventilation dilutes contaminants and increases the exposure time required for exposure to an infectious dose. First, we must ensure that we are effectively providing at least code, or statutory, minimum ventilation to the breathing zone. Increasing ventilation rates from there is shown to have a positive impact on contaminant dilution and lower infection rates. Depending on climate though, increasing ventilation may be limited by existing heating and/or cooling capacity. One can also expect an increase in energy costs associated with treating higher quantities of outside air.
The size distribution of respiratory aerosols is important to understand. As they contain proteins and salts, droplets that may contain multiple active virions desiccate to droplet residue that are mostly larger than the dimensions of the SARS-CoV-2 virus. Filtration efficacy boils down to having a sufficient filter efficiency to address the contaminant size and having the means to circulate air thru the filter. Particulate filters should be at least MERV-13 for non-healthcare spaces. Increasing filtration efficiency, however, comes with a tradeoff. As the Initial and Final filter loading pressure drops go up, so does the energy required to move the air.
Disinfection, especially by well validated technologies such as germicidal UV light, is quite effective at disrupting the microbial DNA/RNA, thus preventing reproduction of the virus. These technologies can all be applied to occupied spaces (upper air systems), in-duct/coil transport path, and for surface treatment.
Studies suggest that humidity control, specifically 40-60% range, can influence infection risk. ASHRAE has recommended 30-60% relative humidity (RH) as an optimal range for decades. We do not fully understand, however, how the coronavirus responds to this measure. There are three hypothesized effects at work here:
- In dry air, particles desiccate faster and to smaller sizes, so aerosol concentration is higher. This is plausible for low humidity but does not explain why infectivity is lower at high RH.
- Dry air can lead to a desiccation of mucosa, which could increase individual susceptibility. Again, this does not explain what happens at high RH.
- The effect of RH on viral survival has conflicting data. Some guidance suggests a linear trend of decreasing survival. Other data suggests infection risk is higher at higher RH.
The expression “long-term” brings an interesting consideration to the conversation. How does resiliency play into our view of HVAC systems of the future? This Covid-19 pandemic and the wildfires in the western United States are raising awareness for the need of building HVAC systems to adapt to, and recover from, indoor and outdoor hazards.
For new HVAC system installs that are on the horizon for contractors (and may still be in the design stage) do you have advice on how contractors should advise their customers who may be concerned they are not addressing the new IAQ concerns that Covid-19 has presented?
This very question addresses why ASHRAE formed its Epidemic Task Force (ETF) to aggressively participate in the risk mitigation response of the Covid-19 hazard. ASHRAE is uniquely qualified to provide guidance on the design, operation, and maintenance of HVAC systems to help reduce the risks associated with pathogen transmission. The ASHRAE ETF has been assimilating research, disseminating risk mitigation guidance, and conducting targeted education for all ecosystem stakeholders. One can find a vast amount of objective based guidance on the ASHRAE Covid-19 resources page.
This topic is vital to understand and respond to. ASHRAE has posted the following statements regarding transmission and operation:
- “Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures.
- Ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air. Unconditioned spaces can cause thermal stress to people that may be directly life threatening and that may also lower resistance to infection. In general, disabling of heating, ventilating, and air-conditioning systems is not a recommended measure to reduce the transmission of the virus.”
Infection control and resilience (the ability to adapt to acute short-term changes in operating conditions) are now in consideration as issues that should be addressed in design thought. How do we provide operational flexibility, while staying on a sustainable path? How do we incorporate a scalable logic that affords multiple operational modes? Owners should start incorporating this resilient thought into basic project fundamentals.
To access ASHRAE’s Epidemic Task Force resources, click the graphic above. Then you will be able to click on individual components to go to those resources.
Is it too early to address potential liability concerns for building owners (and possibly contractors) regarding IAQ? Is this even an issue?
There is still too much about this virus that we do not know. How long can it survive in the air and on surfaces? What is the shedding rate? What are the infectious dose parameters for getting sick? And most importantly, how do we even identify the moment of infection with clarity?
SARS-CoV-2 is clearly a human pathogen that has airborne/aerosol transmission. Given that it is transmitted via contaminated air, it is clear that measures applied to HVAC systems may reduce risk of infection. The HVAC system is an asset that can help mitigate the transmission of this virus. But as indicated earlier, HVAC response is only part of a broader risk response.
Engineering Controls, Administrative Controls, and PPE should all be employed collectively to minimize risk of exposure. Proactively implement guidance now that focuses on responsibly minimizing exposure of the hazard to people, changing the dynamic of people interaction, and having people protect themselves.
What should be the primary considerations when contemplating increasing the amount of outside air into a building?
Increasing the amount of outside air is a proactive technique. In addition to dilution, the exposure time required for exposure to infectious dose increases. These are positive risk mitigation outcomes. Increased ventilation, however, uses more energy when one considers the thermal and moisture control narrative.
Pumping more outside air into the building also has a pressurization impact. Where does that air go? How does it get out of the building? Have unintentional pressure cascades been created that drive contaminant into undesirable locations?
The more prudent consideration is one that considers the synergistic interdependencies of combining ventilation, filtration, and air cleaning effectively. ASHRAE recommends that building owners work with design professionals when considering and analyzing mitigation strategies. Guidance provide by the ASHRAE ETF and other resources should be applied with professional judgement based on unique, individual project fundamentals.
Are contractors “jumping the gun,” so to speak, by promoting proactive measures for manipulating existing (or new installs) HVAC systems in hopes of improving IAQ? Proactive measures include increasing outside air intake, utilizing third-party add-ons like Ionization Grids and ultra-violet (UV) light devices etc. Should contractors wait until there is consensus on a solution before recommending customers invest in these measures?
Proactive measures are available to us now. Many of the items articulated here are shown to be effective risk mitigation strategies; supported by research, studies, and standards.
- Increased ventilation dilutes contaminant and decreases exposure risk.
- Filtration efficiency can be increased to better respond to the contaminant size.
- Pressurization works to isolate/contain spread.
- Air distribution velocities (strong drafts where there are people) can be altered to influence droplet travel.
- Disinfection via germicidal UV light for upper air, in-duct/coil, and space can disrupt the DNA/RNA composition of the virus.
- Humidity levels can alter our susceptibility to mucosa desiccation.
We also have technologies in the marketplace now that claim robust SARS-CoV-2 mitigation efficacy. Such innovation would be welcome news for the built world. Hopefully, peer reviewed research, studies, and standards will follow quickly to support understanding and application of such promising Engineering Controls. The ASHRAE ETF is working on defining appropriate research and standards action. To find COVID-19 resources, visit ASHRAE’s technical resources page.
He is the recipient of numerous awards including the Exceptional Service Award, Distinguished Service Award, Chapter Service Award, Regional Award of Merit, two ASHRAE Technology Awards and the Dan Mills Technology Award.
In addition to his time served on the Board of Directors, Gulledge has served as chair of the Members Council and the President-Elect Advisory Committee, chair of the Finance Committee, chair of the Standards Membership Ad Hoc Committee, chair of the Development Committee for Fundraising, and as an ASHRAE Distinguished Lecturer. He has held ASHRAE Society-level leadership roles on many standing committees, technical committees and presidential ad hoc committees.
In addition to his contributions to ASHRAE, Gulledge’s career in HVAC spans over 36 years. Gulledge is currently a Senior Mechanical Engineer with Environmental Air Systems, LLC. He is registered as a professional engineer in the states of North Carolina, Georgia, Kentucky, South Carolina, Alabama and Virginia.
Gulledge’s comprehensive design, construction and operational portfolio covers a variety of market sectors; including transportation, commercial, educational, institutional, lodging, sports, mission critical, life sciences, healthcare, pharmaceutical, manufacturing, industrial, archival, historical, and hospitality.
Gulledge is a 1983 graduate of North Carolina State University with a Bachelor of Science in Mechanical Engineering.