Boxfan Ambient Air Filter Hack Revisited #3: New Fan and More New Filters

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Blog entry by clagwell posted 06-27-2020 04:50 PM 505 reads 0 times favorited 0 comments Add to Favorites Watch
« Part 2: New Tests and New Filters Part 3 of Boxfan Ambient Air Filter Hack Revisited series Part 4: Two Fans Are Better Than One »

New fan:

The first thing to determine is how much effect the fan shroud has. Testing the same set of filters as the previous post yields this:

With no filter there’s no real difference with the shroud. It increases flow with the MERV 12 by about 14% and 12% with the addition of the MERV 8. That’s not a huge improvement but adding the shroud wasn’t very difficult, at least with the old fan. Unfortunately, the new fan has a different grill that protrudes into the metal frame. This would interfere with a shroud done the same way as on the old fan. Unless there’s a really easy way to take of that interference I don’t think it’s worth the effort. From now on I’m only looking at the unshrouded fan.

I also bought two more filters along with the new fan. One is a basic fiberglass MERV 2 furnace filter that might be more appropriate as a prefilter.

The other is a 2” thick MERV 8. It should have better flow than the 1” MERV 8. While efficiency won’t be as good as the MERV 12 the higher flow rate can make up some of the difference.

The 2” MERV 8 looks pretty good. That would be about 5 exchanges per hour in my shop. The MERV 8 is most effective above 3 micron but that’s most of the dust mass. For the smaller particles the MERV12 will clear the air faster because of it’s higher efficiency for those. I’ll put some numbers on this in a later post.

What this chart shows is that I would need two air cleaners with MERV 12 filters to get close to 5 exchanges per hour. An advantage to that could be better air circulation with proper placement. On the other hand, it’s twice the cost and takes up more space.

Now the filters cost as much as the fans so what about stacking two fans with one set of filters? Next post….

-- Dave, Tippecanoe County, IN --- Is there a corollary to Beranek.s Law that applies to dust collection?

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