Just in! Here's the performance of @JenniferKShea's wedge box with a Utilitech-style fan and two 3M Filtrete 1900 MERV-13 20x20x1 on the back. 🇨🇦 Cost: Fan: $28
Designer adhesive roll: $14
2 Filters: $42
Total: 🇨🇦$84 for estimated 335 CADR (519 sqft room)
It performs like Honeywell's largest air purifier, HPA5350BC (🇨🇦$300 sale price/$380 regular). The Honeywell has a greater turndown range but uses more power.
These are updated values for noise and power, measured at the same time as the ones for the DIY wedge: /2
At lower speed settings though the 2-filter wedge design beats the Honeywell in noise, flow, and power due to its large filter area. /3
Making the wedge air cleaner is straightforward. Hinge the two filters on the inside edge. /4
Position over the rear of the fan with the arrows pointing toward the inlet. /5
Trace cardboard top and bottom pieces and cut them out /6
As with previous versions, optionally cut a channel for the power cord /7
Tape a shroud on the front. For this fan, the optimal is a 13.5" opening. (this came from earlier flow measurements). For other fans, can use tissue paper to see where the flow changes direction. This front shroud greatly increases flow through the filter. /8
I've also added an internal shroud of 21cm diameter with tape. This adds about 2% flow and a small noise reduction. Not strictly necessary. /9
The finished version, sans the decorative adhesive shelf liner. You should also use better tape. The painter's tape I used here was for temporary assembly to test. /10
Here is the wedge air cleaner on the test rig mounted sideways because of the feet. A flow capture hood is attached to the outlet. Backpressure compensation feature was used for the measurements and multiple points were taken to obtain an average. /11
See the earlier 1-filter version thread with other details, including frequently asked questions, such as safety. /12
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
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
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
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...
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?
When an IAQ report for an elementary school states the acceptable industry CO2 guideline is 700 ppm above ambient, or 1200 ppm, ask why the professional is using Std 62.1-2016 Informative Appendix D that was DELETED in 2018 because of misuse and outdated 1950's data.
@O_S_P_E 's calculator will give a target steady state CO2 value based on Standard 62.1 minimum acceptable outdoor air ventilation rates. Hint: It's not 1200 ppm for an elementary classroom. Link: https://t.co/V1DwupuJ3xospe-calc.herokuapp.com
Key phrases identifying that the deleted Informative Appendix D was used:
-Target of 700 ppm CO2 above ambient
-ambient is 300-500 ppm
-majority of occupants be satisfied with respect to human bioeffluents
-uses 1.2 MET, 15 CFM (7.5 L/s), 0.31 L/min