David Elfstrom Profile picture
Aug 16, 2021 15 tweets 4 min read Read on X
#boxfanfilter optimizing:
Fan shroud sizing for Lasko 20" Comfort Fan /1
Drove a screw into the middle /2
Made concentric circles with dry-erase marker /3
Used alternating colors to make it easier to see on the grid /4
Flow capture hood mounted on inlet side, with a 3M Filtrete 1900 (MERV-13) taped to inlet. There is some extra resistance from the capture hood, so actual flow will be a bit higher. Three speeds. 117 V
74 W, -259 CFM, 0.99 PF
59 W, -216 CFM, 0.93 PF
48 W, -166 CFM, 0.87 PF
/5
17.5" diameter: -328 CFM.
27% more flow. Same power /6
16.5" diameter: 338 CFM.
31% more flow. /7
15.5" diameter: -348 CFM.
34% more flow. /8
14.5" diameter: -351 CFM.
36% more flow. /9
13.5" diameter: -341 CFM.
32% more flow. Whoops, too far! /10
Final result: No change in power or power factor. Use between 14.5-15.5", so a 15" internal diameter shroud for the Lasko 20" air circulating box fan.
Speed 3: 74 W. 36% higher flow
Speed 2: 59 W. 30% higher flow
Speed 1: 48 W. 31% higher flow
/11
The fan is noticably quieter with the shroud. I have since removed the tape and will make a cleaner version and measure the noise difference with a calibrated microphone later. /12
Forgot to mention it's a 3M Filtrete 1900, 20x20x1.
If we assume 75% PSE the effective clean air delivery rate is 0.75x 350 = 263 CFM CADR, with 74W power, for an efficiency of 3.6 CADR/W, good for Energy Star (must be > 3.0). Further tests to come!
/13
Optimization so far, with 3M Filtrete 1900 20x20x1

Lasko with 15" shroud: 350 CFM, 74 W

Utilitech with 13.5" shroud: 350 CFM, 52 W!

Actual flow will be slightly higher when measured at outlet with backpressure compensation feature in the flow capture hood. /14
The mains voltage fluctuates (goes higher at night when less demand) and has a large impact on fan power and flow. These numbers are without shroud, with 20x20x1 MERV-13:
115V: 255 CFM, 70 W
117V: 259 CFM, 74 W
120V: 268 CFM, 77 W /15

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More from @DavidElfstrom

May 31
Vancouver Coastal Health has released an updated Ventilation and Indoor Air Quality resource for Schools and Childcare Facilities () but their CO2 page needs some edits. vch.ca/en/document-li…
States high levels of CO2 and other contaminants ... can contribute to [list of five health effects, such as headaches, fatigue, difficultly concentrating], says CO2 should be below 1000 ppm, then says (incorrectly) that health effects from CO2 occur at levels above 5000 ppm. No, those effects can occur below 5000 ppm.  It also states the CO2 concentrations do not indicate a risk of infectious disease transmission in a space. No, ASHRAE's position statement on CO2 states that elevated CO2 concentrations CAN reflect higher risk. Obviously, because it indicates poor ventilation, which IS an i...
Vancouver Coastal Health "CO2 concentrations do not indicate a risk of infectious disease transmission in a space". No.
ASHRAE's position document on indoor CO2 says "higher CO2 conc correspond to lower ventilation and potentially increased risk of airborne transmission"
Vancouver Coastal Health "Note that health effects from CO2 occur at levels above 5000 ppm". Did WorkSafeBC interfere? Because that's contradicted by your Health Canada reference in the sentence immediately before it.
Read 10 tweets
Mar 28
Three years ago on this day ASHRAE stated that Airborne transmission of SARS-CoV-2 is significant.

Today, WHO finally released a model () of #CovidIsAirborne risk by experts in the field. /1 iris.who.int/handle/10665/3…

Landing page for the WHO document titled: Indoor airborne risk assessment in the context of SARS-CoV-2: description of airborne transmission mechanism and method to develop a new standardized model for risk assessment
Four years ago on this day WHO said : "FACT: #COVID is NOT airborne."

Today, WHO finally released a model () of #CovidIsAirborne risk by experts in the field that warned of airborne even earlier, but were shut out. /2
iris.who.int/handle/10665/3…
WHO Tweet March 28, 2020 FACT: #COVID19 is NOT airborne.   The #coronavirus is mainly transmitted through droplets generated when an infected person coughs, sneezes or speaks.  To protect yourself: -keep 1m distance from others -disinfect surfaces frequently -wash/rub your hands -avoid touching your eyes / nose / mouth  Cover page of Indoor airborne risk assessment in the context of SARS-CoV-2
This document has been a long time coming. As described by @jljcolorado, Lidia Morawska, co-chair of the group that published the new WHO airborne model, was previously cut off by John Conly when making the case that #COVIDisAirborne to WHO. /3
Acknowledgements: WHO ARIA Technical Advisory Group:  First name: Lidia Morawska (Co-Chair) (Queensland University of Technology, Australia) (many other names) John Conly (University of Calgary, Canada)
Read 4 tweets
Feb 23
Air purifier manufacturers say HEPA should always be the filter of choice, and their product's proprietary filter delivers. Which HEPA? ISO 35H at 99.95% or ISO 40H at 99.99%? Why not ISO 50U? That's 10x better at 99.999%. Why stop there? Go for ISO 70U at 99.99999%! /1
The answer is, single-pass filtration efficiency DOESN'T MATTER except in specific cases like Powered Air Purifying Respirators (PAPR), clean rooms, operating theaters, or nuclear laboratory exhaust—HEPA's original purpose. /2
For portable/in-room air cleaners, all that matters is the Clean Air Delivery Rate (CADR) for a target particle size and type, within acceptable for sound power and frequency characteristics for the people in the room. /3
Read 13 tweets
Jan 3
Four years into this and we can't keep duct-taping in-room filter solutions for clean air. It's just filter(s) and a fan. We need open-source, optimized design, certifiable product, efficient, repairable using commodity filters and commodity components. /1
We need air cleaners assembled and distributed by not-for-profit community-based social enterprise. No more lock-in to proprietary filters. Verified replacement commodity filtration performance for safety. /2
Low income with donated CR boxes will pay over time in electrical costs for the duct-taped solution for clean air.
Power utilization for Smoke CADR, same filters:
Conventional CR Box: 4 CADR/W. (77 W)
PC fan array air cleaner: 24 CADR/W. (8 W)
/3
Read 4 tweets
Aug 28, 2023
1/ Levoit Core 400S versus Austin Air HM400 in a challenge to see which portable air cleaner removes submicron salt particle aerosols the fastest! Which do you think will win, and by how much? Poll in next tweet below... A large indoor tent with taped seams on a concrete floor is shown. On the left is a bench with instruments. A webcam is mounted on the top of a chair facing the instruments. In the middle are two air purifiers: The cylindrical Levoit Core 400S and the larger boxy Austin Air HM400. In the back right corner is a circular floor fan pointed diagonally upward into the middle. At the front right is a chair holding what looks like a tiny pitcher with a spout. A long thin clear plastic tube is connected to the side of this device, and exits the frame. Power cords are on the floor.
2/ Which has a higher CADR (Clean Air Delivery Rate):
Levoit Core 400S, or Austin Air HM400?
See if you can find the manufacturer's claims for both, and then come back and vote:
[sarcasm] Not only is the Austin Air bigger and far heavier, it also draws way more power, is much louder, and more expensive. It couldn't possibly be *worse* than the Levoit, right? Right?
Read 13 tweets
Jun 12, 2023
When to change the filter on DIY #CorsiRosenthalBox? Holder et al (onlinelibrary.wiley.com/doi/10.1111/in…) showed that performance degradation depends on contaminant: Dust reduces airflow. Smoke kills electrostatic properties. @JimRosenthal4 @joeyfox85 @CorsIAQ Table for MERV 13 single-fi...
@JimRosenthal4 @joeyfox85 @CorsIAQ Note the test substance for the CADR PM2.5 performance measurement was simulated wildfire smoke.
The same would likely apply to a commercial HEPA air cleaner. Monitor for clearing time for a fixed release of contaminant with a simple PM meter.
Read 6 tweets

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