A Dream of Flying Cars

When I haven't had enough sleep, and try to get more sleep in the morning, sometimes odd things happen. Like not having any clear transitions between waking and sleeping, but finding myself with odd memories. Like this morning, where without ever feeling 'asleep' I found myself with memories of a shootout between flying cars. I have no idea what would have inspired that, but presumably I was dreaming in between!

experiments with air purifiers, and Consumer Reports

I have two purifiers currently. A Honeywell 50250 HEPA. And a 12x12 inch MERV 13 filter I taped to an Amazon Basics fan for DIY. I didn't expect the latter to be great, but I thought it was doing something. Now, I have my doubts.

A few days ago, office measured PM 7, I ran my DIY. After 45 minutes PM was 2, woo? But then it stayed for the next couple hours, so I'm not sure that wasn't just air variability.

Today, PM was 6+; with the Honeywell, it was 0-1 within 15 minutes. (I'm not sure my QingPing can measure <1 without wobbling.) Later I paid more attention, and even on low mode, PM was under 1 in 10 minutes.

Then I wondered how my DIY would do against high load. I fried one strip of bacon... and overshot; PM went to 999, which as high as my monitor goes. Oops. I moved the DIY in, closed the door, and waited. After 20 minutes, it was down to 893, and I wasn't sure if that wasn't just leakage/escape. Thing is, the kitchen area isn't that big (though that's complicated by literal holes in the interior walls.) 1000 cubic feet and 40 cfm should still cycle most of the air in 25 minutes, and hopefully reduce PM by like half (MERV 13).

Then I tried the HEPA. After just 1.5 minutes PM was 750. 9 minutes, 200. Whoosh.

I wondered if maybe DIY had done the hard work of getting under 999. Switched. 6 minutes, PM maybe went from 155 to 148. What if I ran nothing? 10.5 minutes, 148 to 140. So the DIY is maybe doing something, but just 2x natural leakage.

I then worried if the HEPA was biased: it blows straight up, and my monitor was on top of the fridge, near the stream. So I moved the monitor, and numbers stalled for a bit, but still, 140 to 48 in 5 minutes.

Honestly, given the volume and CFM, the Honeywell seems maybe too slow: it should be cycling the air every 4 minutes, and through a HEPA filter! But it's undeniably faster than this DIY.

A well made DIY, like a Corsi-Rosenthal box fan, is said to be very powerful, like 250 or even 400 CFM, for cheap. Maybe, but I sure didn't touch that. And if I ever do build another one, I'll want to test it, just as you should fit-test respirators. I wonder if I can get a particle source other than frying something or making popcorn.

Relatedly, I ordered a Levoit Core 300, for use in another room, and future travel. _Then_ I signed up for Consumer Reports, to read their air purifier reviews. They gave it low numbers... but also, I was not impressed with their reviews. They give high ratings to big purifiers with low CFM/$. They don't give precise numbers of their own, like CFM ACH or CADR. The more detailed Levoit reviews actually seemed great -- bunch of pro, no cons. So why the mid ratings? Totally unclear Also one of the reviews said "rated for 0 square feet" which uhhhh.

Where's the site that will tell me if CR has gone downhill?

Levoit Core 300

Ordered this last night, arrived this morning. Amazon is good at what it does...

Supposed to weigh 6-7 pounds, but it's _bigger_ than I envisioned. I was expecting something slightly larger than a personal air purifier, this is much bigger. Not sure it would even fit in my backpack and if it did, it would fill most of it. Traveling with it would be somewhat awkward. Could maybe do it if I dump my winter stuff, or else expand to a second piece of luggage.

The top speed is loud-ish (supposedly 50 dB elsewhere) but a lot quieter than top speed of my Honeywell 50250. Possibly quieter than the quiet mode of the Honeywell. Of course, lower power: 140 CFM (cubic feet per minute) vs. 250, for the top speeds. It may also be that the Honeywell needs a filter cleaning.

Power: top speed took 15 minutes to reduce office PM2.5 of 7 to under 1.

It has 3 main speeds, and a night mode. Low speed is definitely audible but not big. Night mode is almost silent, but then I wonder how much it's doing. There's _some_ air flow. Sadly, none of these purifiers or fans seem to give ratings for less than top speed.

Why I did order this one? It seemed small plus rated as both cost-effective and quiet on graphs like this: https://twitter.com/marwa_zaatari/status/1598180050893148160 or https://twitter.com/LibDemPatrick/status/1598460782408351744
And double checking myself, it had CFM/$ of around 1.4, with little in the HEPA space beating that, apart from discounts. (I did find later that Taotronics is having a huge sale on one, 176 CFM for $60. Sale like that might mean they're discontinuing it and you should buy your replacement filters now.)

By the way, it's been maybe 20 minutes on low (not night) speed and PM is still under 1, so it's keeping up with whatever's leaking in. Probably too soon to really tell, though.

air purifier caution

So I like my new Levoit, and they seem good overall. But there's something to look out for. If you find a page comparing their many different models, you might scan down, and see something like

Core 200S -- 176 sqft -- $89 -- 7 pounds

Core Mini -- 176 sqft -- $49 -- 2 pounds

and you might think the Mini is a great deal. Or you might smell a rat and dig deeper. And if you dug, you would find that Levoit is coy about the CFM/CADR of the Mini, but buried somewhere you can find a line saying it's 2 changes of air per hour for that 176 sqft. Whereas all the other models are rated at 4.8 air changes per hour. Which means the 200S is around 112 CFM but the Mini is 47 CFM. Not such a great deal.

Lesson: don't choose a purifier until you've really pinned down its CADR, in whatever units you like. "Covers a room of size X" cannot be trusted unless they also say how many air changes (ACH) that's for.

I view this as shady on Levoit's part, but then the whole market sector is a mix of good engineering and shadiness. You've got people selling basically the same thing for 2 or 3 times the price. You've got add-ons that don't work or are outright dangerous (ionization and ozone-generating UV).

I should also note that I wrote most of this based on memories of their own website. On Amazon, I see the 200S sold as "ideal for 183 sqft" in the fine print, but the headline is "up to 915 sqft" -- which only works at 1 air change per hour...

while, heh, the Amazon Core Mini page has an explicit 46 CFM for the Mini vs. 140 for the 300. So now it looks not so much disappointingly shady as just inconsistent marketing.

(Though I also note the Mini is "HEPA" and not "True HEPA". Another thing to look out for. And has an aroma dispenser which I wouldn't want.)