I forgot to post that big quiet air purifier number 6 is done :). Unfortunately the cost of materials and parts is now $512 cad. Cheaper/better motor and driver boards are the low hanging fruit to get that down maybe by $85. Num 7 will be back to 400 rpm max, this one only does 350.

Big quiet air purifier number 5 is now done. 1110 cfm flow through merv 13 filters with one 36.3 dBa noise 300 rpm and no motor hum etc., just the blades whoosh. Goes up to 350 rpm for more flow. And I honestly don't know what to do with it. Sent out some emails looking for takers.

And now, a bunny. Which happened to be in my images gallery and it's worth sharing :D

It's time to declare victory for big quiet air purifier number 4. It can be controlled over Wi-Fi, and measures airflow, remembering and comparing flow to when the filters were new to give a percent flow indication. With a latest fan model it would get 1110 cfm @36.3 dBa, 1450 @ 47 dBa. However

Big quiet filter box cad is coming along. To recap, should get the same noise to cadr relationship as a set of about $3500 cad of the next best machines, like the medify a-112. Plus a fraction the running cost and better building automation integration, and filter health sensor.

Another day another air quality scam. Do you suffer from excessive capitalist exploitation? Why not buy more crap in a desperate but totally ineffectual attempt to get clean air? Only $5.99!

I assembled another big quiet filter box today! I measured the pressure drop across the filters with the fan at 300 rpm. It's basically the same for the 3M filters and these cheaper dafco filters. So flow is probably also the same. So this is good. The cheap filters are about as good!

I'm experimenting with putting hardware cloth on the big quiet fan to prevent anyone from putting their finger in there. It still won't stop pencils which could damage the fan but at least no humans get hurt in that scenario.

The version 11 big quiet fan is slightly quieter than the version 6! I measured it this morning. The actual reading was only 40 dBa, background was 36, so about 38 dBa including reflections! And higher pressure/flow, somehow, not clear how that happened. 8% more!

I shopped around for a micro manometer, a very sensitive air pressure sensor. They want $900 for one with a resolution on 1 Pa, unclear accuracy. The sdp-125A sensor datasheet claims 0.1 Pa accuracy near zero, datasheets are usually legit. So I built my own. $35.

V5.0 of the big quiet fan is working great! The pressure and flow is the same but the noise is even less. So step by step it's getting better, but to be clear I've already delivered on the promises made for the schedule thus far, improvements are bonus from here on out :).

Printing of the big quiet fan v5.0 is complete! I plan to test it later today :D. You heard it here on bluesky first :)

After solving many issues in many ways, the cad for the v5.0 big quiet fan is done and the printer is working and it's printing! If no issues should be ready for testing in two days.

I tested a bunch of flow straighteners for the tw4. The best one gives a 23% pressure boost in one dir at lower throttles! But it's only 10% boost in the other direction. Still, it improves the noise in other ways, so it's a win. Will do a few more tests, stabilize and call this good.

I've used some of what I learned from the big quiet fan to add a flow straightener to the tw4/wm12 erv. Using the built in pressure sensor, the pressure, and thus flow, is up 14%. It's an extra part or two but it also makes it quieter and allows me to eliminate the lul more completely.

Testing

The giant printer lives again! It's printing a fan frame for the big quiet fan project :. Should take about 30 hours and 1.4 kg of plastic.

See that v of filters at the top? It's supposed to go inside the box below it. I just realized I could get two of them, a w rather than a v. Maybe even three. This is the way to go because the cost per unit clean air of the filters does not change if you have more filters!

The big fan jigsaw puzzle is progressing!