Thread by @strawthatbroke

So as promised, yesterday I conducted a relatively simple test of my small desktop HEPA filter unit. Let me walk you through it.
(1/12)

https://twitter.com/strawthatbroke/status/1468160148875223044

The first step was a design modification based on something @PlasticFull said to me and I quote “HEPA hates leaks”. It was clear to me that my V0.1 slots for the HEPA filter were just too wide for the filter thickness, so a quick re-cad and 24 hours later, V0.2 was born.
(2/12)

Next came the test setup. For this I bought a large 0.57m x 0.43m x 0.37m box giving me an internal volume of 0.091m3. I put some regular draft excluder around the lid to make it reasonably air-tight.
(3/12)

Inside the box I put one of these cheap air quality monitors, £25.99 from Ebay. I know it's not a @sensirion but I thought I would limit the expense in case the whole thing was a complete failure. Perhaps @sensirion might donate one to the cause 😜
(4/12)

Next, I used a couple of old web-cams and loaded up NCH Suite for the video capture. All I needed was a chopped-down piece of incense and my test was ready to go.
(5/12)

Having let the air quality meter settle, I started the video, lit the incense and closed the lid. The meter doesn’t data log to my PC so I would have to transcribe it from the video later. Here is the hugely edited video of the test.
(6/12)

Key points (edited video time code):
🔹Fan Off
🔹Incense goes in at 0:15, burns for approx 30 mins (it gets smokey in there)
🔹The meter saturates at PM2.5=1000, PM10=1786 (1:05)
🔹Fan on (1:17)
🔹Getting clearer (1:50)
🔹Meter moving down (1:55)
PM2.5=0, PM10=0 at end!
(7/12)

Now to plot the graphs of the air-quality meter readings. Plotted is the whole test cycle and also the start phase and the air-filtering phase.

The saturation of the meter is clearly visible in these plots.
(8/12)

I plotted the rate of filtering with a best-fit line.

Unsurprisingly it's better at filtering larger particles compared to smaller. Not sure whether the rates of filtering are good, I suspect they are OK for a unit this size, definitely better than no filtering at all.
(9/12)

In conclusion, IT WORKS!
I was worried that it might just blow air around.This might be bad in classrooms.But it filtered the air!

30 of them running as a first line of filtering alongside a bigger unit in the room🙂

And don’t forget,it's right in front of the student.
(10/12)

Extra info:
🔸Freecad for CAD
🔸Ultimaker Cura for model slicing @UltimakerGB (really impressed with print support generation)
🔸@3DFilaPrint for PLA filament
🔸@anycubic3dprint Mega-S 3D printer

Happy to be contacted by any of these companies if they can offer support
(11/12)

@CorsIAQ
@JimRosenthal4
@theAliceRoberts
@dgurdasani1
@DrEricDing
@DrAmirKhanGP
@chrischirp
@rhysthomas
@wesstreeting
@IndependentSage
@iRobot_UK
@ARCTIChannel
@kprather88
@jneill
@AirbonPurifier
@cv_cev
@hivetosurvive
@HoppySaul
@Dr2NisreenAlwan

All input/retweets welcome
12/12