CU Boulder held a virtual webinar on Tuesday, February 2nd, led by Doctor Mark Hernandez. The presentation explained the effectiveness of HEPA filters on classroom air freshness.
The webinar summarized data gathered in a joint University of Colorado Boulder and Denver Public Schools(DPS) study that focused on air quality in schools. The results show a need to prioritize old schools in the deployment of high-efficiency particulate air (HEPA) filters in classrooms.
“Old buildings are designed for warmth, not high throughput airflow,” Dr. Hernandez said.
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Dr. Hernandez and his team found that many schools they tested take 20 minutes or longer to completely recycle air. In some cases only 20% of that was fresh air, presenting further problems.
“We shed a lot, on the order of 100,000 to one million microbes every hour,” Dr. Hernandez said. “There is a storm of stuff floating around us.”
For schools without modern filtration systems, this creates a backlog of particles that need to be filtered. These particles are made up of biological and non-biological elements. The biological elements can potentially carry disease and viruses such as COVID-19.
Dr. Hernandez saw this at Cheltenham Elementary school off West Colfax Ave. A newly constructed wing of the building filtered air particles much more efficiently than the original classrooms. The building was originally constructed in the 1920s.
This has to do with building materials, the type of ventilation system. The old wing had radiant heat, the new wing had a centralized ac installation.
The results made Cheltenham Elementary an excellent candidate, and Dr. Hernandez and his team deployed their HEPA filters. The resulting data proved that HEPA filters put in older classrooms improves air quality. This in turn takes the burden off old HVAC systems.
This has also allowed DPS to prioritize schools and avoid sending resources to a location that may not have needed HEPA filters in the first place.
After about thirty minutes, the webinar opened for questions. A member of the audience asked Dr. Hernandez how this data can be applied in other settings like museums.
“Different venues based on occupancy and occupancy patterns should have different ventilation requirements,” He responded.
Elaborating on this, Dr. Hernandez advised that we should “be conservative” with standards due to the differing nature of venues. He noted that a museum is a “walkthrough venue” whereas a school is not.
“If we have a standard, it has to actually be something that we can implement,” he said.
For now, Dr. Hernandez and his team have provided DPS with data they need to safely bring children and teachers back for in-person learning.
Currently, only early childhood education and elementary schools are hosting in-person classes. The remaining grade levels are using some form of hybrid or online schooling.
Boulder Valley School District is currently completing a return to in-person classes.
Contact CU Independent Staff Writer Alexander Edwards at Alexander.Edwards@colorado.edu