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9 Apr, 5 tweets, 2 min read
Naaah, the massive gym outbreak couldn't possibly be lack of #ventilation. That rooftop unit is in excellent condition. 😬😬😬
I don't even know what I'm seeing. Is that charred polyisocyanurate spray insulation?
To be fair it's only one of six units, the others appear to be better.
It could be "decommissioned in-place", as they say. There are 5 other units serving the gym that appear to be in better condition.
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More from @DavidElfstrom

David Elfstrom Profile picture
10 Apr
LISTEN as highly influential Prof John Conly (upper left) of UCalgary, AHS CV19 sci advisory grp, Public Health Agency Canada, Chair WHO Infection Prevention & Control R&D Expert Grp. opposes N95 wearing citing acne harm vs @DFisman & @kprather88 precautionary principle. /1
"there's been decreased O2 concentrations in pregnant women" yeah, well here's the reference from one of his publications, dissected in fine form by @caruzycki /2
Here's an example of Prof Conly's influence by the dedicated @jmcrookston /3
Read 8 tweets
David Elfstrom Profile picture
7 Apr
What's the risk of COVID in apartment buildings? This review covers much of the basics but I believe the prevalence is much higher ... (THREAD) /1
ncceh.ca/documents/evid… Screen shot of PDF document
We've long known air flows throughout a building despite walls and floors because there's strong driving forces and little attention to air sealing, both on the building envelope, and between units. /2
Figure: Ueno, Lstiburek, Bergey 2012 buildingscience.com/documents/bare… Simplified diagram of stack effect in multifamily buildings
The three driving pressure forces are: Wind, Stack (chimney) effect, and Mechanical (both negative and positive). /3
Figure: Air Leakage Control for Multi-Unit Residential Buildings, CMHC 2017 agency.coop/media/747/down… Image from PDF showing the forces acting on buildings
Read 16 tweets
David Elfstrom Profile picture
18 Feb
#COVIDCO2 readings in an Ottawa classroom. Never reached a steady state. At 3152 ppm every breath contains 7.2% of other people's breath‼️‼️ 🤮. #DontShareYourAir #Onted
Classroom has below 0.4 air changes per hour.

Target MIN: 3-4, Good: 4-5, Excel 5-6, Ideal 6+
/1
For COVID, air changes from HEPA filtration are equivalent to outdoor air. Typical classroom portable HEPA air cleaner:
400 CFM on max at 65 dB adds 2.7 ACH
200 CFM on med at 55 dB adds 1.3 ACH.
Two on med would be 58 dB.

BUT there's still the cognitive impact of 3000ppm!
/2
Here's the back-calculation assumptions used to reach 0.4 ACH in a classroom. I'm assuming 12 foot ceilings for an older naturally ventilated school. Other values are typical as well. The calculator throws an exception in red at 19 students, but not at 18.
/3
Read 10 tweets
David Elfstrom Profile picture
6 Feb
CBC Marketplace and UofT's Dr Jeffrey Siegel tested 3 samples of 5 models of air purifier, including the DIY box fan with MERV-11 filter, which was better than the Dyson #filtration cbc.ca/news/business/…
The Marketplace/UofT tests did not consider how loud the air purifier is on its highest setting, which can be a limiting factor for practical use.
cbc.ca/news/business/…
Also consider the Clean Air Delivery Rate per Watt of power. ENERGY STAR air purifiers are tested for both.

Link: energystar.gov/productfinder/… Screen capture of web page
Read 8 tweets
David Elfstrom Profile picture
2 Feb
ASHRAE guidance on in-room air cleaners for reducing COVID-19 in the air (Jan 21, 2021)
@ShellyMBoulder
Link (PDF): ashrae.org/file%20library…
/1 IN-ROOM AIR CLEANER GUIDANCE FOR REDUCING COVID19 IN AIR IN
Stick to the basics of filtration. Beware of some technologies used by portable air cleaners: Ionizers, UV-PCO and other names may claim to remove or destroy contaminants but may convert them to other compounds that may be harmful
Link (PDF): ashrae.org/file%20library…
/2 In-room air cleaners may contain one or more technologies de
Good example of sizing a portable air cleaner for a classroom with a MERV-8 filter already present in the HVAC system to achieve 6 air changes per hour equivalent.
Link (PDF): ashrae.org/file%20library…
/3 Example of how to choose the right size: A 45 x 20 ft (14 x
Read 13 tweets
David Elfstrom Profile picture
31 Jan
New plain-language guidance for reducing virus transmission in schools using HVAC systems, by @HRAI_Canada

#Ventilatio, #filtration, UV, CO2 meters, humidity, portable air cleaners

Link (PDF):
hrai.ca/uploads/userfi… Reducing the Risk of Virus ...
HRAI has also reached out to school boards and Education Ministries Canada-wide to ensure decisions concerning #ventilation and #IAQ in schools are informed by the best available information.

mediaedgedigital.com/supplierinsigh…
Since children are likely to be the last to receive a vaccine, we must continue to push for indoor air quality funding.

The lasting benefits of better academic performance and reduces absenteeism of students & staff alike are worth it. /3
Read 4 tweets

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