David Elfstrom Profile picture
Jan 11 15 tweets 10 min read
The air cleaner purchased by @nseducation for schools has a Clean Air Delivery Rate almost HALF of a common retail unit and may create secondary products by reacting with gas phase contaminants in a poorly ventilated room using photocatalytic oxidation #nspoli /1 Guardian Beyond Air F159E: ...
As seen in the photo, it's not running on its highest setting. For #ventilationequity in non-mechanically ventilated classrooms, should be a min 15 CFM per person, or 375 CADR for 25 people, AND at an acceptable noise level. How many per classroom? #DoTheMath! /2
Don't get me wrong, any filtration is better than nothing! But it's a mere band-aid over a gaping wound.
A DIY $120 #corsirosenthalbox will beat the air cleaners purchased by @nseducation AND can be used in STEM lessons! See cleanarair.com /3 Screen capture of web site
On the product claims of ActivePure® technology "to reduce over 99.9% of many common contaminants in the air and on surfaces", Dr. Brent Stephens who runs the Built Environment Research Group, has umm, "done the research". Link: built-envi.com/what-air-clean… /4 Image
But what about the use of photocatalytic oxidation? There are questions about chemicals that can be inadvertently created from this. I'll refer to the experts who wrote an open letter: medium.com/open-letter-to… /5
We should be requesting independent monitoring of the chemical composition of secondary products in both gas and particle phases in the rooms where these devices have been installed. You know, precautionary principle? /6
Stick with layering the basic triad of engineering controls:
#Ventilation
#Filtration (#FilterFitFlow)
#UVGI
please hold the bells & whistles /7 Image
Similar advice is from Johns Hopkins Center for Health Security in their letter released today.
#Ventilation 6ACH #Filtration MERV-13, #UVGI, #HEPA or build #Corsirosenthalbox, don't use unproven additive technologies: centerforhealthsecurity.org/news/center-ne… /8 Image
Take solace my NS friends, because your neighbors
@NLESDCA bought at least 3000 of the smaller Aerus Pure & Clean for schools, with a max flow of only 60 CFM (and presumably lower actual CADR rating, if it even qualified for the AHAM test) /9
Update on the cost: Nova Scotia spent $2.3M for 1600 units, or $1438 each. Compare with the Honeywell unit from Canadian Tire that has nearly twice the verified air cleaning performance for $329. globalnews.ca/video/8501732/… /10
If the Beyond Guardian Air was quieter, that might be worth the much higher cost, but it's not. It's the same noise level at full speed with almost half the air cleaning power as a much less expensive Honeywell. /11 Both the Honeywell HPA5350B...
There is a wide variety of air cleaners available. Many have significantly less noise and/or significantly more Clean Air Delivery Rate. @marwa_zaatari has collected info on many of them and their cost (USD) and noise level here: /12
Prof Jeffrey Siegel @IAQinGWN weighs in with this 7-minute interview, and I fully agree. While this unit might create byproducts using PCO, it's not as problematic as being undersized for a classroom without mechanical ventilation. Listen here: /13 cbc.ca/listen/live-ra…
@IAQinGWN These air cleaners are covered in this article /14 saltwire.com/atlantic-canad…
@IAQinGWN Summary table (excluding maintenance costs and the concerns about secondary products formed by Aerus' photocatalytic oxidation), includes suggested number of units for typical non-mechanically ventilated classroom. Take-home: Aerus is 8x higher cost. /15 Image

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More from @DavidElfstrom

May 5
When your board of health hires an unqualified MOH who can only be Acting, you get a minimizer who ignores the 51%-80% prevalence of Post-Acute COVID-19 Syndrome and recommends treatment of chicken noodle soup and ginger ale. simcoereformer.ca/news/local-new… (May 4, 2022) Perfectly healthy, fully-va...
Post-Acute COVID-19 Syndrome is no picnic. Link to PDF from Public Health Ontario: publichealthontario.ca/-/media/Docume… Screen capture of the top h...
“Strauss said he is of the view that COVID-19 is an extremely low-risk disease for individuals who are up-to-date on their vaccines, and relatively healthy” Again, ignoring PACS prevalence of 51%-80%
Read 4 tweets
May 2
Welcome to Strausslandria, Ontario, where apparently “COVID was 10x more deadly than the flu... Today, flu is more deadly than COVID on average because our population is so highly vaccinated” /1 @JacobShelley norfolktoday.ca/2022/05/02/moh…
Flu is now more deadly than COVID? Where's your reference for that, Dr. Strauss? Compare with “the mortality risk of COVID versus flu is likely greater than 24 times” (h/t @DGBassani @LadyScorcher) /2
Dr Strauss goes on to say, “there are non-pharmaceutical interventions available” (referring to mandates and lockdowns) “that work but when removed people will start getting COVID again”.
He completely ignores engineering controls available that haven't been utilized. /3
Read 4 tweets
Apr 22
Will Dr. Conly complain that today's award overstates his influence? After all, he complained to the CBC ombudsman in part because it described him as “An influential Canadian doctor and top adviser to the WHO” in reporting his controversial views of N95 respirators. Dr. John Conly  F.N.G. Starr Award for lifetime achievement
Dr. Conly is the primary & corresponding author of WHO commentary article stating "SARS-CoV-2 not airborne to any significant extent, respirators offer no advantage & may result in unintended harms" aricjournal.biomedcentral.com/articles/10.11… /2
It somehow seems so much worse when he says the same thing out loud: /3
Read 5 tweets
Apr 16
The Levoit Core 400S is a quiet and economical air purifier. I bought two of them for the kid's bedrooms and put one through some tests.
TLDR: Recommended! No conflicts of interest, this is self-funded. @LevoitLifestyle /1 Table of measurements for Levoit Core 400S. Contact @DavidEl
@LevoitLifestyle The Levoit Core 400S is compact. There is an app to control units from your phone over wi-fi (the "S" indicates "Smart"). The sleep mode automatically turns off the display. It is quieter than my laptop in sleep mode. /2 Photo of Levoit Core 400S on a wood floor
@LevoitLifestyle There is a PM 2.5 μg/m³ sensor and display. I will leave others to critique how reliable this sensor is. For now assume it's a general indication. The app displays historical 15-minute interval graphs including the PM values. PM sensor is below the label. /3
Read 14 tweets
Apr 16
The Ontario Energy Board has proposed an optional enhanced time-of-use price that would see residential/small commercial pay just 2.5¢/kWh overnight to encourage EV charging and battery storage, in return for a peak rate of 10x, or 25¢/kWh. /1 news.ontario.ca/en/release/100…
With behind-the-meter battery storage and PV panels, along with increasing carbon price on natural gas, this could finally tip the balance in Ontario from gas towards heat pumps, ushering in cost-effective low carbon home heating and cooling. /2
The full report (PDF) is available from the OEB at: oeb.ca/sites/default/… /3
Read 4 tweets
Apr 10
Thread on why a typical building may be safer in spring and fall than any other time of the year:
Mild temperatures during the shoulder seasons result in the highest outdoor air change rates compared to winter and summer: /1 Scatter plot showing at low and high outdoor temperatures th
This is because of the economizer function on HVAC equipment. Due to solar gains and heat from people and equipment, it's warmer inside than outside. If the outdoor air is cooler than inside, use it instead of running mechanical cooling (air conditioning). /2 Outdoor air fraction for an idealized economizer cycle showi
We get the most outdoor air when an outdoor air damper is fully open, typically at the switchover point between heating and cooling (~15°C / 69°F). /3 Scatter plot showing at low and high outdoor temperatures th
Read 6 tweets

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