1/ Another reminder that this global pandemic is far from over. Vaccinate fully to lower chance of severe outcome if infected AND significantly lower chance of infection by significantly reducing inhalation dose of virus-laden respiratory aerosol particles.
2/ Wear a high quality mask/respiratory, e.g., N95, while indoors in public/work spaces or crowded outdoor spaces in close contact, increase ventilation where possible, have meeetings outdoors. Not rocket science.
3/ Employ particle filtration, including proven #HEPA air cleaners and #CorsiRosenthalBox es., & employ when feasible upper-room UV to inactivate viruses in respiratory aerosol particles. Not rocket science.
4/ We have had the tools needed to significantly
reduce inhalation dose of virus-laden aerosol particles (and thus reduce spread of infection greatly) for the past 2 1/4 yrs & most for 2 1/2 yrs, but still not making ample use of those tools, folks.
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1/ I love teaching. It has been a passion thorughout my career. I am so excited that my proposal to teach a first-year seminar course in fall was accepted. The course title is "(Almost) Every Breath You Take" and will be a quarter-long exploration of indoor air quality.
2/ Students will learn basics about indoor pollutants, their sources, human exposure, and engineering controls. They will learn about & measure rebreathed fraction of air (fraction of every inhaled breath that came from the collective respiratory systems of others in a space).
3/ Students will also learn about and observe indoor chemistry in action through use of everyday consumer products, and (of course) design, build, and test #CorsiRosenthalBox es.
Quick cost calculations and benefits of each in a 700 ft2 classroom. These ARE a cost-effective means of lowering inhalation dose of virus-laden respiratory aerosol particles in schools, folks.
2/ HEPA: The 3-year average annual cost of lowering inhalation dose with a good, popular, HEPA air cleaner that achieves CADR = 300 cfm, accounting for capital cost, recurring filter and electricity costs (at 9 hr/ school day during school year) is less than $9.95 /student/year.
3/ HEPA continued. This situation would lead to a steady-state reduction of virus-laden respiratory aerosol particle concentrations in classroom air of approximately 60% if starting w/ a classroom ventilation rate of 2 ACH (2/hr).
Just a thread about ozone inside buildings ... meant as an introductory step in a journey ....
Outdoor ozone is the ubiquitous source of indoor ozone, although some indoor sources do exist (photocopy machines, laser printers, and some air "cleaners").
2/ The plot on the LHS shows ozone concentrations measured on the roof of a school we studied over a 4 day period along with nearby O3 concentrations at a State-run Continuous Air Monitoring Station. Lower curves are O3 concentrations in 3 classrooms.
3/ The peak ozone concentrations in 2 of 3 classrooms are roughly 1/4 of peak outdoor concentrations. The third classroom had almost no supply air during the 4-day period, which means very little outdoor air conveying O3 in + ample time for any O3 that does enter to react away.
1/ I agree, @JimRosenthal4. Some misperceptions in this blog. Really unfortunate and I hope it will be deleted, corrected and re-posted for that reason. I will dissect one by one according to the four points.
2 / Point 1. Just simply wrong numbers for CADR (by far). No idea where the author came up with these numbers. They look more like single filter on fan (but even worse that that). Please see below from a peer-reviewed paper in a high impact journal (not a blog).
3/ These values of CADR are 4.3 to 8.4 times higher than those listed in the blog. A four filter system would be slightly less, perhaps 3.5 to 7 times higher.
1/ Despite its very high clean air delivery rate (CADR) - see below - that can significantly lower inhalation dose of virus-laden repiratory (and other) aerosol particles in shared air when occupants are present, the #CorsiRosenthalBox also helps between occupancies.
2/ Example for typical (approx average)-sized HS classroom we studied in Central Texas, but also applies to many K-8 classrooms during lunch periods/recess. How long does it take to purge a reasonably well-mixed (assumption more valid w/ CR box) of 95% of aerosol particles?
3/ We found that using ASHRAE 62.1-2019 for occupancy and area-based classrooms the typical ACH worked out to 2.5 to 3.5/hr. Sadly, a large fraction (approx 80%) had lower ACH than this standard.
Increased ventilation is important for lowering pollutants of indoor origin (BOTH particles and gases), including virus-laden respiratory aerosol particles. Doing so does come w/ a cost & energy penalty (very dependent on location).
2/ My colleague, Atila Novoselac @ut_caee, has done extensive analyses of HVAC systems in schools in Central Texas, a relatively hot and humid climate.
3/ I asked him if he could run the numbers for energy use (integrated heating & cooling periods) in a 700 ft2 unit ventilated classroom (fairly typical) for 9 hours per day during an entire (occupied) school year in Austin to achieve a ventilation rate of 7 ACH.