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
The stack effect is a dominant factor in winter, and is directly related to the height of the building AND the temperature difference between indoors and outdoors. Remove the temperature difference and the stack effect is minimal. /4
Figure: Cdn building digest number 104, 1968
Wind effect can exert very strong pressures that overwhelm other pressures, from minutes to hours, causing significant air movement within a building. /5
Figure: Handegord & Hutcheon, Building Science for a Cold Climate, 1983
Dynamic pressures on a building can be very high. Note a 5 Pa pressure difference from a kitchen exhaust fan in a home is enough to backdraft a naturally aspirated hot water tank in the basement. /6
Figure: plot based on physics Plot of wind pressure vs wind speed
Mechanical pressures: It depends. Nearly all MURBs use corridor positive pressurization with fresh air to make up air exhausted from suites from kitchen and washrooms. Typically these flows are not balanced between units at all. /7
Figure: CMHC 2017 agency.coop/media/747/down… Air movement in buildings in winter
The implications are that in cold climates in winter, there are significant amounts of uncontrolled air movement between suites, sometimes substantially more than the intentional air supplied by mechanical systems. /8
Figure: Fitzgerald & Bohac, 2012 slideshare.net/mnceeInEx/mf-s…
*IF* any centralized exhaust fan is off, there is a potential for direct connection to other units with flows driven by wind, stack, and remaining mechanical pressures. /9
Figure: Center for Energy and Environment multifamily ventilation assessment 2016 cards.commerce.state.mn.us/CARDS/security…
In Ontario alone there have been outbreaks reported in the news of MURBs in London, Sudbury, North Bay, Collingwood. All of these had significant numbers, all were in winter. There are likely many more, but health units aren't aware of them because they are overwhelmed... /10
Dr. Alex Summers: A heavy load of case area-wide and the ability to notice trends contributed to delay. "It wasn’t until we had a few weeks of seeing this common address pop up multiple times, that we were able to see that trend and declare outbreak" /11 london.ctvnews.ca/why-did-it-tak…
So what can those in mid-rise and higher apartments do?
⛔️DO NOT cover up exhaust vents, or block the suite door, they exhaust stale air and provide fresh air!
✅Check with toilet paper for this necessary air movement out of and into the suite. /12 Toilet paper test at suite door
✅Look for areas of uncontrolled leakage entering the suite from other suites. Pipe penetrations are common. /13
Figure: slideshare.net/mnceeInEx/mf-s… Gaps around sink plumbing
Pandemic or not, if kitchen & washroom exhaust fans are not functioning (toilet paper not sticking to the grill) or worse, slight air movement into the apartment, bring it to management's attention immediately.
/14 Toilet paper should easily stick to an exhaust vent.
Remember, #COVIDisAirborne.
Properly functioning mechanical systems help.
Portable HEPA air cleaners will provided lasting indoor air quality benefits.
Open your windows a crack.
Wear a tight-fitting quality respirator outside your home.
Don't panic: Be aware of shared air. /15
Whoops, forgot the figure. You want central exhaust fans to be operating. If not, there's potentially direct connection to other suites.

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More from @DavidElfstrom

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+
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!
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.
Read 10 tweets
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.
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
2 Feb
ASHRAE guidance on in-room air cleaners for reducing COVID-19 in the air (Jan 21, 2021)
Link (PDF): ashrae.org/file%20library…
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
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.

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
15 Jan
New preprint from J Lednicky & al: Isolation of SCV2 from air in a car driven by a COVID patient with mild illness. (Jan 15 2021).
While virus detected at all sizes, "Remarkably, viable virus was only detected in particles 0.25um to 0.5um)"
Automobiles are one of the worst places to be. Roll down windows, wear good, well-fitting masks, and especially use NO recirculation.
"The patient drove the car for 15 minutes w/windows closed and the A/C on, then parked it and exited, leaving the windows up and the air sampler running for an additional 120 minutes. Total collection time of 135 min to
sample 1.22 m3 of air within the vehicle"
Read 4 tweets
14 Jan
BREAKING! Ontario Society of Professional Engineers @O_S_P_E calls on the Ontario government @ONgov to IMMEDIATELY address the #airborne transmission of COVID-19 to help slow the spread.

Summary thread follows

"OSPE and its engineers believe a key piece to our defence against this virus has not been properly addressed by the Ontario government - the need for proper #ventilation and air #filtration to stop the spread of the virus via #aerosol particles"

"OSPE believes that airborne transmission is one of the main reasons why we are seeing so many outbreaks in schools and long-term care facilities across the province"
Read 9 tweets

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