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David Elfstrom Profile picture
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2 Nov, 5 tweets, 2 min read
I'm already seeing 6 Air Changes per Hour as a blanket number. However this depends on volume, or rather, the ceiling height vs floor area and occupancy. A rough guide might be:
12 ACH small volume (vehicles)
6 ACH average (office, classroom)
3 ACH large vol (arena, warehouse)
Houses and apartments are quite a bit different: ASHRAE has an entirely different standard just for residential #ventilation! Easier to think of per person amounts.

Try for 30 CFM per person for COVID-19 but no less than ASHRAE 62.1 Table 4-1a in ASHRAE 62.1-2019
Drat. I meant no less than ASHRAE 62.2

By the way, the relevant pandemic ASHRAE standards are available for free to view on their website, which I greatly appreciate. <glares at CSA>
Here's where to find the ASHRAE pandemic-relevant standards. Have to view them on the web by following the links from this page, direct linking will not work: ashrae.org/technical-reso…
For homes, see today's excellent post from Dr Shelly Miller:

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More from @DavidElfstrom

David Elfstrom Profile picture
3 Nov
Wow, this is what I've been advocating for Ontario school boards since August!

The School District of Philadelphia is measuring the outdoor air amount supplied by mechanical #ventilation of every room in every school. THREAD #onted
They use 15 CFM per person of outdoor air as the threshold.

Technically, ASHRAE Standard 62.1 is 10 CFM/person plus 0.12 CFM/sqft. If there are 18 persons in a 750 sqft room it works out to the same.

You can view the ASHRAE standards from this page: ashrae.org/technical-reso… Recommended healthy air flo...
Back in August, I recommended posting a sign on each school room:
Read 13 tweets
David Elfstrom Profile picture
20 Sep
BREAKING
CDC changes COVID-19 guidance, airborne is primary way the virus spreads, touching surfaces is NOT the main way. #Ventilation is important, as it goes beyond 6 ft and remains suspended in the air.
H/T @jljcolorado & @jmcrookston Comparison of text from archive.org showing difference betwe
Canada, you need to revise your guidance to be in line with science, known since February. Add breathing and inhalation. Minimize surface transmission. Add poorly ventilated spaces as risk factor, remains in the air and travels greater than 2m indoors.
canada.ca/en/public-heal…
One-stop must-read by the top aerosol scientists:
FAQs on Protecting Yourself from COVID-19 Aerosol Transmission
This document is frequently updated.
Shortcut: tinyurl.com/FAQ-aerosols
Read 8 tweets
David Elfstrom Profile picture
31 Aug
HVAC is trending in #Ontario.

Let's clear the air, #onted.

It should be immediate #VENTILATION, with filtration improvements, for a #SaferSeptember to buy us time, and Indoor Environmental Quality improvements (#IEQ), for the long term. Not generic 'HVAC'. Not "AC".

THREAD
We say we urgently need quality HVAC in schools (we do!) but HVAC is:

(H)eating the building,
(V)entilating using outdoor air, and
(A)ir (C)onditioning,
where AC = removing heat and moisture.

ALL classrooms have H and V, though often no AC.
In old schools Ventilation was provided naturally, using a chimney effect to cause negative pressure in the school, drawing outdoor air inside. It's unreliable, so these schools were later retrofitted with exhaust fans to force the air out. (if you find unrenovated, send pics!)
Read 20 tweets
David Elfstrom Profile picture
24 Aug
1/ #VENTILATION is a key factor in #SafeSeptember for #onted. In this thread I'll cover:

🔸My immediate 3 asks of @sfleece and @fordnation

🔸A suggested room-by-room assessment and implementation methodology

🔸Who to follow Photograph of a rusty rooftop classroom exhaust fan that was
2/ My immediate asks of Ontario:

1⃣ Update the Guide to Reopening Ontario's Schools to add #ventilation, currently absent. I recommend using Schools for Health: Risk Reduction Strategies for Reopening from Harvard School of Public Health schools.forhealth.org/risk-reduction…
3/
2⃣ Also update the Guide to Reopening Schools to reflect current knowledge regarding the relative importance of airborne transmission of COVID-19 compared to surface transmission.
Read 39 tweets
David Elfstrom Profile picture
13 Aug
What was the ventilation requirement for your school when it was designed? Have rates been measured this summer and repairs made (tighten fan belts, open dampers)? Have portable HEPA air cleaners been added to low-ventilated rooms? #SafeSeptemberON #onpoli
Older schools with natural ventilation didn't necessarily achieve 30 CFM/person but it was certainly more than in the 1980s
That dip in the 1980's was a response to the energy crisis. It resulted in sick building syndrome. If smoking was present, outdoor air rates had to be 25 CFM/person, though good filtration with recirculation permitted reduced rates, the floor still being a mere 5 CFM/person.
Read 8 tweets

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