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I'm building a small wood shop air cleaner to suck dust floating in the air. I understand a radial blower (squirell cage) is usually used to get some static pressure to overcome the resistance cased by the filter (for instance: Record Power 400). But as a radial blower is more expensive and quite a bit louder, I'm hoping to get about the same suction using two 19 cm (actual blade size) computer case fans (Spectre Pro 23 cm / 156 CFM / 1.81 mm H2O air pressure).

I understand that that putting them parallel doubles the air flow and putting them in series doubles the static pressure - not affecting the air flow much compared to one fan, but I still have a couple of questions with this:

  1. Does putting the fans in series give anything like the same static pressure like the Record Power 400 has? Just an educated guess... (the Record 400 is just an example of the approximate filtering capacity I'd like)

Also, putting the fans in series doubles the static pressure, but is it that simple in an air cleaner where there is a under pressured air chamber/cavity (the space between the filter and fans) in front of the fans? Obviously two fans in parallel would cause a bigger under pressure in this cavity.

  1. So which would filter better, the two fans in series giving more static pressure or two fans parallel giving a greater under pressure in the cavity between the filters and the fans?
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  • $\begingroup$ Compare the static pressure delivered by the two fans to that from the filter - then you know what you need to do. $\endgroup$
    – Solar Mike
    May 27, 2020 at 6:43
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    $\begingroup$ I suspect that a computer fan in a room will have an almost negligible effect on room dust removal. sure, a filter would fill up, but the dust collected versus the dust in the air will be quite small. You need to move air to have an effect on the cleanliness of the room. Like enough air to make a breeze. $\endgroup$
    – Tiger Guy
    May 27, 2020 at 19:43
  • $\begingroup$ Yes comparing would do it, but that would mean that two different enclosures would have to be built first... trying to avoid that. =) $\endgroup$
    – jugi
    May 28, 2020 at 15:50
  • $\begingroup$ Well, a 19 cm fan does give some breeze and two even more, but after putting a filter in front of them, I'm not so sure they have the static pressure... $\endgroup$
    – jugi
    May 28, 2020 at 15:53

3 Answers 3

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To catch the dust in a 50 cubic meter shop requires an air transfer rate of about one complete air change per minute. That means your fan has to pull in at least 50 cubic meters of air in a minute and stuff it through the filter. Your computer fan runs at 156 cubic feet per minute which is 4.5 cubic meters/minute which means you'd need more than ten of those fans to do the work, assuming no pressure drop in the filter.

A much wiser choice is to catch the dust at its point of origin and filter just that air instead. If the dust source is a table saw, you put a vacuum cleaner hose right next to the blade inside the saw housing underneath the table and seal that space off. Running the vacuum cleaner will then draw air down through the blade slot in the table and prevent the blade from throwing dust into the room. All the dust will wind up in the vacuum cleaner and you don't have to filter the entire volume of air inside the shop to accomplish this.

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Well, the 19 cm computer fan had some jitter to it and at least one problem was a blade not at the same level as others. I tried to rectify that, but of course broke the blade off.

So of to plan B - or C ;)

I came to think that car parts are cheap enough and they seemed to have ready made radial fans, motor and everything. So I guess I'll order one of those for the air filter. Should work nicely.

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  • $\begingroup$ Car fan is probably 12V DC , is that your power source ? $\endgroup$
    – blacksmith37
    May 28, 2020 at 18:53
  • $\begingroup$ I can easily make it that - so yes. $\endgroup$
    – jugi
    May 28, 2020 at 20:05
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The volume of air in the shop needs to be known prior to any equipment being specified to accomplish your goal. That being said, your current attempt is never going to get results of any significance whatsoever. What's the volume of air in your shop?

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  • $\begingroup$ The shop is about 50 m3. >>your current attempt is never going to get results of any significance<< Why do you say this? There are examples of this kind of filtering. This air filter isn't supposed to move junks of air at once, but just slowly pass air through. And if it's silent it can basically be left on all the time. $\endgroup$
    – jugi
    May 28, 2020 at 20:13

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