David Elfstrom Profile picture
P.Eng, Energy management, measurement & verification. Born @ 327 ppm CO₂. Safer infrastructure, #ventilation, #CorsiRosenthalBox optimization
Dame Chris🌟🇺🇦😷 #RejoinEU #FBPE #GTTO🔶️ Profile picture Aviva Gabriel Profile picture Eric's Mild Adventure Profile picture Potato Of Reason Profile picture Cawir Ginting Profile picture 7 added to My Authors
May 25 4 tweets 2 min read
Aerosol particle emission increases exponentially above moderate exercise intensity resulting in superemission during maximal exercise (2 W/kg+).
So spin class outbreaks weren't caused by droplets aerosolizing after hitting the bike's flywheel? [sarc]
pnas.org/doi/10.1073/pn… October 2020:
May 5 4 tweets 2 min read
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...
May 2 4 tweets 2 min read
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
Apr 22 5 tweets 2 min read
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
Apr 16 14 tweets 10 min read
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
Apr 16 4 tweets 1 min read
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
Apr 10 6 tweets 2 min read
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
Apr 4 18 tweets 8 min read
The next time someone denies the use of a portable air cleaner in a classroom on a (false) basis that it might spread infection by moving air, or interfere with the HVAC system, show them this paper. @amandalhu @sameo416 (HT @Poppendieck).
onlinelibrary.wiley.com/doi/epdf/10.11… /1 When determining the amount of outdoor air provided to a space, ASHRAE Standard 62.1's Zone Air Distribution Effectiveness factors to account for the inefficiency of air delivery and mixing to provide outdoor air to the breathing zone. /2
Apr 3 8 tweets 3 min read
Insufficient ventilation at arena causes fog in the stagnant air over the ice between the plexiglass. CO₂ rose constantly without end until intermission, when we left, at 2000 ppm.
Great show! We wore our respirators, few others did. Some coughing behind and beside us. Dew point was approximately 4.5°C
Mar 21 4 tweets 2 min read
The power was out this weekend so I decided to reclad the ELFSTRÖM in final permanent form: /1 Box fan with outlet shroud and box mounted on the inlet side I used vinyl adhesive shelf liner to wrap the box. Still using painter's tape to mount the filter - makes it easy to change the filter and won't ruin the vinyl adhesive pattern. The filter gets sucked on when running anyway. /2
Feb 2 4 tweets 3 min read
Highly recommended! Detailed summary of the main engineering controls for airborne infection control to reduce transmission indoors:
#Ventilation #Filtration #UVGI
👇 #DoAllTheThings! Implement multiple engineering controls to reduce airborne infection and improve indoor air quality
#Ventilation
#Filtration
#UVGI Image
Jan 20 4 tweets 3 min read
Having a CO₂ meter with visible display can enable an educator to be a manual version of a demand-controlled ventilation system, with control over the indoor environment using windows (Source: Di Gilio et al 2021, pubmed.ncbi.nlm.nih.gov/34224708/) #COVIDCO2
HT @Billius27 "Fig. 5 are shown the ... @Billius27 If a CO₂ display was in my daughter's mechanically ventilated classroom, her teacher might have opened the windows, or moved to another room after seeing rising levels. Principal: waiting for parts to repair the HVAC system. Daughter developed common cold symptoms 48h later. Image
Jan 12 8 tweets 4 min read
Very exciting news on the #corsirosenthalbox front! @CorsIAQ & @CappaSnappa thanks for the (Elfstrom 2021) reference, it made my day! Some comments & questions follow: /1 "AHAM recommends that CADR is 2/3 of floor area" Yes, it's floor area = 1.55 x sqft. That's for 8' ceiling with 1 ACH residential outdoor air exchange, described in Annex E of AHAM AC-1 2020: /2
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
Dec 14, 2021 11 tweets 5 min read
My wife & daughter traveled to @sickkids @SickKidsNews today for an appointment.

Several lapses occurred at screening. Most egregious:
They were made to remove their CA-N95 respirators for the blue surgical mask, shown below.

Let's go through all of them: /1 Photo of left hand holding ... Your policy is to protect everyone, especially those at higher risk of COVID-19. How is downgrading masks consistent with that? What is the "right" amount of protection, anyway?
My wife and daughter were NOT offered the option of masking overtop. /2 Several extracts from unive...
Dec 9, 2021 7 tweets 4 min read
Swiss study finds SIX TIMES the cases in poorly ventilated classrooms (those with over 2000 ppm CO₂) compared to better-ventilated ones. #COVIDCO2
#Ventilate2Educate #COVIDisAirborne
H/T @SamJCauston
swissinfo.ch/eng/society/st… More details on the Swiss CO₂ classroom study here: empa.ch/web/s604/covid…
Dec 9, 2021 5 tweets 3 min read
While #Ventilate2Educate is geared towards schools, we can #Educate2Ventilate with simple directives for small businesses & organizations. Simple low-cost changes can make for an enormous indoor air quality improvement. Low-rise small commercial buildings are everywhere. Simplified schematic of small business rooftop unit: Maximiz These simple ventilation actions and more are described on the CDC's Ventilation in Buildings Page: cdc.gov/coronavirus/20…
Dec 7, 2021 8 tweets 4 min read
Uh oh @GEDSB. My daughter's classroom was doing well in the fall with CO₂ levels below 800 ppm, so I stopped sending the logger. After my presentation last night with @DFisman, I decided to check it again. #COVIDCO2 /1 Levels below 900 ppm until ... This is a school with full mechanical ventilation. This room is centrally provided so air is shared with other classrooms.
Filters have NOT been upgraded to MERV-13 or better.
HEPA is only in the rooms required by the province. Not in this classroom. /2
Nov 25, 2021 4 tweets 2 min read
Genome sequencing analysis shows spread of new variant in HK in hotel quarantine between suites across from each other when the air flowed to the corridor. Here we go again—no amount of positive pressure in the suite is acceptable. /1
h/t @nzm8qs news.gov.hk/eng/2021/11/20… If there is a 5 Pa positive pressure difference between the suite and the corridor, air will shoot out under the door continuously at an average velocity of 2.1 m/s (higher in the centre). No open door required. For a 10 mm bottom door gap, that's 19 L/s (40 CFM) of flow /2 Graph of average velocity (...
Nov 7, 2021 10 tweets 4 min read
#corsirosenthalbox flow tests for Lasko 3733 and 3M Filtrete 1900 20x20x1 filters.
Shroud optimization: 20 cm radius (15.75" diameter) /1 Effect of shroud size on outlet flow. Having a shroud is important, but don't stress over it. Without it, air flows backwards at the corners instead of through the filters. /2
Sep 5, 2021 13 tweets 5 min read
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