The COVID-19 pandemic has created a lot of challenges for buildings, the most pressing of these is keeping occupants safe. We have learned a lot about the disease since the pandemic first started. One of the biggest revelations has been that the virus can be spread in the air, as an aerosol, as well as through direct contact. As this fact came to light, building operators had to look for guidance on what to do with their HVAC systems to help stop the spread. The organization that leads the way for these types of recommendations is The American Society of Heating, Refrigerating and Air-Conditioning Engineers or ASHRAE. This global organization brings experts together to craft recommendations for HVAC systems in large buildings in a way that advances their goal “to serve humanity by advancing the arts and sciences of heating, ventilation, air conditioning, refrigeration and their allied fields.”
When the world first started learning about the COVID-19 virus, ASHRAE created a pandemic taskforce for the purpose of studying how buildings can minimize infections. These recommendations, like our general body of knowledge about COVID, have changed with time. The tough thing about ASHRAE’s job is that many of the recommendations they make have unwanted consequences. Requiring more outside air increases the energy needed to heat and cool buildings, making them less sustainable. Asking for denser filters can put a strain on a building’s ventilation systems and can cause fans to burn out or decrease occupant comfort. ASHRAE is careful to study all of the negative possible consequences of their recommendations before making their declarations.
At first, ASHRAE recommended bringing in as much outside air as possible and using much higher rated filters. Filters use a Minimum Efficiency Reporting Value, or MERV system, that goes from one to sixteen. Under normal conditions, offices are recommended to use MERV six filters. Now ASHRAE says, “Our current recommendation is to use a filter with a Minimum Efficiency Reporting Value (MERV) of 13, but a MERV 14 (or better) filter is preferred.” All of these recommendations make it harder for buildings to serve the needs of their customers and make it harder for them to hit their energy usage and sustainability targets but they are seen as necessary precautions in order to protect people from a deadly disease.
When it comes to filtration, there are a number of different types of filters that can be used to disinfect a building’s air. The most common types are made out of some sort of mesh filter that can catch particles down to a certain diameter. This process is rather straightforward and therefore rather well studied. Another filtration process that is also widely used, but whose function is much less straightforward, is bi-polar ionization (or BPI) filters. By using electricity, these filters are able to charge floating particles in a way that both makes them fall from the air and pulls the hydrogen atom away from organic compounds like viruses and bacteria in a way that kills or inactivates them.
As for the effectiveness of BPI filters on the coronavirus, the verdict is still not out. We spoke with William Bahnfleth, Professor of Architectural Engineering at Penn State University and head of the ASHRAE pandemic response taskforce, about this somewhat controversial filtration process. He told us, “The problem is that it takes a long time to conduct and evaluate tests on the safety of any new technology. We know BPI filters are good at removing particles out of the air but the question of where they go is yet to be determined.” The concern is that these particles fall onto surfaces and can lead to ‘fomite’ transmission, another way of saying transmission by contact with infected objects.
It isn’t just where the particles go that is a problem. “There is also some concern that one of the byproducts of BPI, hydrogen peroxide and ozone, are harmful to humans,” Bahnfleth explained. The levels of hydrogen peroxide and ozone that are produced by most BPI filters is reported to be well within the acceptable range when it comes to human consumption but those reports come from the manufacturer themselves and have not been independently verified.
The CDC is in the process of creating verified, independent studies about the effectiveness of BPI versus its possible negative side effects but the length of time needed for them to be complete will likely mean that they won’t come out until after the pandemic is over.
Right now the CDC uses this guidance around BPI filtration and ASHRAE has followed suit: “If you are considering the acquisition of bi-polar ionization equipment, you will want to be sure that the equipment meets UL 2998 standard certification (Environmental Claim Validation Procedure (ECVP) for Zero Ozone Emissions from Air Cleaners) which is intended to validate that no harmful levels of ozone are produced.”
Although, they do issue a disclaimer to using this type of filtration: “Relative to many other air cleaning or disinfection technologies, needlepoint bi-polar ionization has a less-documented track record in regard to cleaning/disinfecting large and fast volumes of moving air within heating, ventilation, and air conditioning (HVAC) systems. This is not to imply that the technology doesn’t work as advertised, only that in the absence of an established body of evidence reflecting proven efficacy under as-used conditions, the technology is still considered by many to be an ‘emerging technology.’”
We all want to find a way to put an end to the pandemic. For buildings, this means having to create new cleaning measures and find ways to disinfect the recirculated air we breathe. But we also have to realize that any change we make to the way our buildings are run can have their own negative externalities. BPI filters could be a powerful way to disinfect our indoor environments. But, they have not been fully studied so buyers should remember that most of the information they are getting about their effectiveness and adverse effects are coming from the vendors themselves, with their own agendas. Even after this pandemic is over, what we learn will likely be important for any other types of viruses that we might encounter. If, god forbid, we do see another widespread pandemic like this one, hopefully, we will have more information about different air filtration techniques by then.