As we all do our part to ‘flatten the curve’ of the coronavirus pandemic, everyone also recognizes the importance of educating ourselves. EEI’s commissioning expertise focuses on optimizing the built environment. We can’t tell you more than you probably already heard, read, or discussed regarding the medical side of coronavirus. However, EEI cares about the health and safety of our staff, clients, and all of you reading this. So, our newsroom will cover pertinent topics regarding infection control, remote monitoring of systems, and engineering advances related to facilities.
Last week, we shared ASHRAE’s article, Guidance for Building Operations During the COVID-19 Pandemic. The article offers quite a few suggestions for infection control in facilities. COVID-19 is so new that no one knows very much about it. This is true from the medical perspective and from the perspective of a building engineer trying to reduce risk of virus transmission in a hospital. We’re in a, “do your best with what you have” moment, and over time we hope we will be able to determine which actions are most effective. When it comes to reducing risk with heating / air conditioning systems, engineers and building operators seek to reduce the number of infectious viruses in the air. If you think of this like cottonwood puffs during cottonwood season, the more puffs that are floating in the air, the more likely you are to bump into one.
Our Series on Ventilation
In part 2 of our series on the ASHRAE article, we explore suggestions for Air Filtration as it relates to hospitals. Our experts on healthcare commissioning and indoor air quality researched what we know about the pandemic and put together the following Q&A on the topic.
Q: Does increasing filtration level work to remove viruses from air?
- A: We think so but can’t quantify how much. The list below explains why.
Virus particles are tiny! Perhaps smaller than 0.125 microns (a human hair is 100 microns).
- Most hospital air systems already have very high filtration levels. Commonly used filters in hospitals include Minimum Efficiency Reporting Value (MERV) and High Efficiency Particulate Air (HEPA). ASHRAE Standard 170 requires all clinical spaces to use MERV 14 filtration, the most commonly-used level of MERV filter. We often see a higher level of filtration for surgery areas with HEPA filters, and ASHRAE requires HEPA filtration for airborne infectious isolation rooms and protective environment isolation rooms. Older systems may not meet these current standards and can be considered for increased filtration.
- Even high levels of filtration might not fully eliminate all coronavirus particles. This 2016 paper published in Methods of Microbiology, states that Coronaviruses similar to COVID-19 are approximately 0.125 microns in diameter, which is smaller than the size filters are tested against (0.3 microns). This is not the exact virus we have now, but it addresses several multiple similar Coronaviruses.
- We require more data to get the full answer. This FAQ link from the National Air Filtration Association provides information without being definitive. It suggests that like everyone else, the filtration experts have insufficient data about the specific problem of COVID-19. Filter ratings indicate the percentage of particles of the tested size (0.3 microns) that filters capture. We know that filters capture some particles smaller than the size they are tested for like COVID-19, but we don’t know how much or what percentage. We would expect that higher-rated filters will also capture a higher percentage of smaller particles, but we don’t yet know.
Q: What should be considered before increasing filtration level?
- A: Check your systems for items in the list below.
- Filtration Levels
- HEPA filtration removes a minimum of 99.97% of particles in the air with a diameter equal to 0.3 microns. There are HEPA filters that are rated for a higher percentage of particle removal, but they are still based on 0.3 micron particles.
- We use the MERV system to describe other filters. The higher the MERV rating number, the “better” the filtration. It is not common to see MERV filters higher than MERV 14.
- Fan capabilities. Since increasing filtration creates more resistance to fans, we can “run out” of fan power and end up reducing the total airflow to the space, which reduces dilution. It’s important to know what additional capacity your fans have before you increase filtration level. Fan curves, combined with recent / most current test and balance reports, variable speed drive readouts (Hz, Amps) or fan amp measurements can help predict whether your fans can handle increased filtration.
- Filter racks – depth. Filter racks may not be large enough to accommodate higher filtration filters that are typically deeper. Some higher filtration levels are available in thinner filter format; these usually create greater resistance (pressure drop) and need to be changed more frequently.
- Filter racks – frame type. MERV filter racks are not the same as HEPA filter racks; it’s not usually possible to increase to HEPA without modifying or changing the filter rack.
- Filter racks – sealing. Even if you do not plan to increase filtration levels, make sure filter frames have proper sealing. Sealing between the filter and the supporting frame will prevent air from bypassing around the filters. Consider foam materials made for filter frames such as Neoprene/EPDM or Vinyl Nitrate. For side-access channel type filter frames, consider using tape on the upstream side of the filters.
- Filtration Levels
Our engineers will continue to share insight on commissioning, engineering, mechanical systems, and the coronavirus over the coming weeks. Please send us your questions!