Do I still need to override my Ventilation Controls?
Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning - Albert Einstein
A little over a year ago, when the Covid-19 pandemic began changing life as we knew it, we began making changes in any area that we thought might make a difference. Some of those changes led to reductions; others may have been more based on wanting to do something and less based on science. Perhaps it was the best science available at the time, but over the next year, our understanding of what is and what is not effective has improved. With the emergence of a vaccine and a growing percentage of the population now receiving the vaccine, it seems we may be heading back towards something that more closely resembles pre-pandemic life.
Along the way, many of the responses rightfully adjusted as our knowledge increased, but one initial reaction seems to have remained, and it might be time to think about that one again. The adjustment I am referring to is the air exchange ratio in buildings. While there is no doubt that poor air quality leads to poor health, and there is an optimum number of air exchanges that need to occur, in many cases, buildings have overridden the air exchange controls. They are simply conducting a full “flush” of outside air constantly.
When we reflect on the initial responses to the pandemic, rightfully so, we started to question whether or not the HVAC system could contribute towards the spreading of Covid-19. This was interesting as, at the same time, we also began focusing on the airborne travel distance of the virus, and most established that limit at 6-10 feet.
If you have looked at the air return system, even in your own home, chances are the filters, and conditioning elements are well beyond 10 feet from the air return. The larger the building, the even further those elements of the system are. So we already have a math problem, the pathogen in question is believed to travel roughly 6-10 feet before it settles on a surface, and when it enters an air return system, we likely have a much great stretch of duct than 10 feet to get to the mechanical equipment and filtering mechanism. Yet, in some cases, we are installing ultraviolet light and other countermeasures at that equipment to address Covid-19 concerns.
That is not to say UV Lights in an HVAC system cannot serve a purpose. Lights placed near coils can prevent the growth of mold and harmful bacteria. Lights placed in the ductwork can also help address other pollutants and allergens that have reached the UV light. In fact, if Covid-19 reaches the UV light, it is effective in destroying the outer protein coating of the virus, rendering it inactive. The key question is if. So while UV lights have demonstrated effectiveness in improving air quality, it may not be a magic bullet for Covid-19 (source).
We also need to think about what we know about the primary ways the disease is spread indoors. You might recall when the pandemic first took hold, many of us were leaving our groceries in the garage for a few days before bringing them in. If we brought them in, a lot of disinfecting was occurring before things hit the pantry. We didn’t know, and why take a chance. But as we learned more, the CDC began to change its guidance on surface transmission and landed on that surface transmission, while possible, is not considered the main route by which SARS-CoV-2 spreads, making the risk of surface transmission low. Cleaning remains an important strategy, as does hand washing, but in general, surface transmission even amongst a non-vaccinated population is considered low risk (source).
Overwhelmingly, evidence points towards the risk of spread really lies in human to human spread. When humans are concentrated in an area, the humans are the most likely source of spreading disease, so let’s dissect that for a moment..
Recent CDC Guidance for fully vaccinated people states that additional prevention steps are unnecessary for most indoor activities (or outdoor activities). This May 13 article by the CDC provides specific examples of what is safe for vaccinated people and what is not safe for unvaccinated people.
So taking this a step further, many buildings installed a sensor to help Building HVAC systems understand when more humans were in a space and thus when ventilation rates might need to be increased. That sensor - a CO2 sensor. In fact, pre-covid, this was considered one of the most effective ways to control indoor air exchange rates. CO2 sensors read when CO2 levels are increasing - and then calls for increased air exchanges. CO2 levels decrease, air exchanges aren’t needed as frequently, and the system reduces the number of air exchanges to meet human occupancy.
This begs the question: As we continue to reach greater vaccinated populations, do we need to continue to override our air exchange controls? Perhaps a more effective mechanism is to use (or install) CO2 sensors, so those air exchanges occur when they are needed and don’t occur when they do not.
This doesn’t mean you can ignore good indoor air practices. We still need improved filtration, we still need air exchanges, we still need properly maintained equipment. We still have irritants, allergens, mold, and other pathogens that require monitoring and air exchanges. But what it may mean is the time of overriding all of the controls and constantly flushing out the building may be coming to an end.
That is good news if you are paying the energy bill. Constant conditioning of outside air is costly, both in financial terms and in environmental terms. In nearly every life circumstance, going to extremes is not beneficial, and the same can be said of the HVAC response to the Covid pandemic. As we have learned more, as a greater number of occupants are no longer spreading the disease, perhaps it is time to rethink our strategy of overriding those controls. It may be time to turn back on the CO2 sensor (or install them) and provide a more effective and efficient solution.
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Stay well!
Chris Laughman is the ThirtyNine Blog author, a blog dedicated to reducing the built environment's impact. When not blogging, Chris is helping the real estate industry reduce energy and water impact as the Vice President of Sustainability for Conservice, the Utility Experts. Whether Multifamily, Single Family, Student Housing, Commercial, or Military, we simplify utility billing and expense management by doing it for you. Our insight into your utility consumption provides an opportunity to identify risks. Leveraging innovation and experience, we ignite solutions with real impacts and track performance to ensure the trendline stays laser-focused on the goal. To get there, we must build relationships within our organizations and outside of our organizations building the critical mass needed to truly make a difference. We have before us a tremendous opportunity. Standing shoulder to shoulder, we will get this done. Contact me at claughman@conservice.com for more information.