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15 Aug, 4 tweets, 3 min read
Adding a HEPA filter to every @tdsb classroom is #equal, but NOT #equitable.
To approach #ventilationequity, non-mechanically ventilated classrooms need multiple units, in this case three on medium speed.
For justice, @ONeducation must fund capital repairs to @Fix_Our_Schools Equality, Equity, Justice i...
The math of #ventilationequity:
I can't identify the artist for the equality/equity/justice infographic. Thank you for your work!
(in case that's unclear, I have been unable to identify who the artist is, would give credit if I knew)

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More from @DavidElfstrom

David Elfstrom Profile picture
5 Sep
Canadian Aerosol Transmission Coalition calls on federal party leaders for stronger, consistent COVID-19 protections:
1⃣Messaging on aerosol transmission and airborne protection,
2⃣clean air ventilation standard,
3⃣HEPA filtration, and
4⃣respiratory PPE. /1
Remember the prescient quote by the late Justice Archie Campbell, head of the 2003 SARS Commission:
📢“If we do not learn from SARS and we do not make the government fix the problems that remain, we will pay a terrible price in the next pandemic” /2
The Canadian Coalition on Airborne Transmission is a multi-disciplinary group includes physicians, health scientists, ventilation engineers, respiratory protection specialists and occupational health professionals. 6-minute video: /3
Read 13 tweets
David Elfstrom Profile picture
3 Sep
#COVIDCO2 monitoring success story 👇
You don't need to have permanent CO₂ monitoring in classrooms with mechanical ventilation. You can have The Littlest Hobo CO₂ that helps out for a few days and then moves on.
(Unintentional reference to an actual HOBO CO₂ monitor)
Read 4 tweets
David Elfstrom Profile picture
3 Sep
Really cutting it down to the wire @GEDSB. I can't find the ventilation reporting that is required by Ministry of Education memo B16 to be posted on your website *today*. Many other boards were able to provide this information weeks ago, and some went beyond the minimum.
Here's an example to follow.
Okay, so I missed the green box on the COVID reporting page which I thought was for cases. Here it is
Read 5 tweets
David Elfstrom Profile picture
30 Aug
Just in! Here's the performance of @JenniferKShea's wedge box with a Utilitech-style fan and two 3M Filtrete 1900 MERV-13 20x20x1 on the back. 🇨🇦 Cost: Fan: $28
Designer adhesive roll: $14
2 Filters: $42
Total: 🇨🇦$84 for estimated 335 CADR (519 sqft room) Image
It performs like Honeywell's largest air purifier, HPA5350BC (🇨🇦$300 sale price/$380 regular). The Honeywell has a greater turndown range but uses more power.
These are updated values for noise and power, measured at the same time as the ones for the DIY wedge: /2 Image
At lower speed settings though the 2-filter wedge design beats the Honeywell in noise, flow, and power due to its large filter area. /3
Read 13 tweets
David Elfstrom Profile picture
25 Aug
One year ago, this was my jump into trying to clear the air around school #ventilation (wherein I miss-tagged Ontario Minister of Education @Sflecce) now at 48 tweets.
Photo is a rooftop classroom exhaust fan turned off because it was too noisy.
That fan is used to force infiltration in through cracks in the building envelope and intentionally open windows. It was a valid design for several decades for ~25% of classrooms in Ontario, ~5% are fully naturally ventilated, and the rest have a HVAC system /2
Some of these have been or are being retrofitted to add ventilation with federal flow-through funding. It's about 🇨🇦$43,000 to add a unit ventilator to a classroom, based on AMDSB @yourschools which is ensuring all its schools have mechanical ventilation! /3
Read 8 tweets
David Elfstrom Profile picture
22 Aug
FINAL OPTIMIZATION! Box fan single filter with 400 CFM measured at 120V. Estimated clean air delivery rate is 248 CFM CADR. Power is just 53 W, placing it well into Energy Star level for air cleaners. Room size: 384 sqft (8' ceilings). Cost: 🇨🇦$55 plus some tape. /1 Image
The filter is a single MERV-13 3M Filtrete 1900 which has the lowest pressure drop of the whole range. I also tested a Tex-Air 20x20x2 MERV-13 and there was no significant difference, it was 0.7% less flow, within measurement variation. /2 Image
Lifting the filter away from the back of the fan adds 8% more flow, and if cut a circular hole with 21 cm radius instead of a matching square, it adds another 3% more flow. /3 Image
Read 26 tweets

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