Improved Air Filtration

[Russ Webb]

I built my shop in 2012 and have been continuing to refine it since. Because of my location I built the shop to be extraordinarily well insulated and air tight. The upside is it costs me virtually nothing to heat in a cold climate and is comfortable year round. The downside of being so air tight is that there is very little air exchange so any dust I generate stays in the shop (at least for 8-9 months per year).

My power tools are not terribly sophisticated and I don’t have good dust collection. The result of a very tight shop and crappy power tools and lousy dust collection is that in the last three winters I’ve suffered from persistent bronchitis - a condition I’ve never experienced before. So, in addition to going on a quest for better dust collection at the tools I embarked on a quest to increase the efficiency of ambient air filtration.

I’ve had a couple of Jet ambient air filters (AFS 400 and AFS 1000) for quite awhile and they’ve been helpful. But, obviously I needed to do something more to reduce the persistence of fine dust in the shop air.

I looked everywhere for sub-micron filters that could replace the finer secondary filters in both my Jet ambient air filters. I could find nothing that would do much better than the 1 micron Jet replacement filters. Given my struggles with bronchitis I concluded that I needed much finer filtration than that. I stumbled across a video by Stumpy Nubs in which he replaced his Jet AFS 1000 secondary filter with a sub-micron Wynn Environmental filter designed for a cyclone dust collector. Stumpy’s version was clever and located the filter well below the AFS 1000 connected by a flexible duct.

I don’t have the floor space to allow remotely locating the filter like Stumpy and I didn’t want to have to run any ducting because I felt it would reduce the efficiency of the systems. In looking for dust collectors I noticed the Oneida systems that transitioned from a rectangular plenum exiting their dust collectors to a cylindrical HEPA filter. So, I decided I could build a plenum that would make a short transition from my Jet AFS filtration equipment to very fine filters intended for cyclone dust collectors.

I ordered a couple of filters - one from Oneida intended for the Mini-Gorilla cyclone system that provided 40 sq feet of HEPA filtration and another from Wynn Environmental that provided 230 sq ft of (the 13”x34.5” MERV 15 nanofilter). I built a plenum to attach the Oneida filter to my Jet AFS 400 and one to attach the Wynn filter to my AFS 1000. The Oneida filter has a fixture at the bottom allowing for attachment of a standard 2.5” shop vac hose to help in cleaning the filter when it needs it. That seemed like a good idea so I built a bottom for the Wynn filter that allows for attachment of a shop vac hose that is covered with removable Lexan so I can monitor when the filter might benefit from cleaning. This lets me use compressed air to blow dust free from the inside of the filters while vacuuming from the bottom it to increase cleaning efficiency.

I hung both filters facing each other high on opposite walls of the shop with the idea that doing so would be beneficial to air flow. This has proven of no consequence since air flow from the filters is diffused in a large cylindrical pattern and does not create the kind of directional flow that resulted from the original AFS filters. In doing so I considered the advice that mounting the filters high would just pull fine dust up past my face and create problems. But, in my shop there was just really no other place to put them. Also I had previously bought a Powermatic PM 1250 air filter and mounted it inches off the floor under a table on casters that I can position near my work to pull dust I generate from hand tools at the bench, sanding, etc.

The result will, I think, be much cleaner air. The combined Jet AFS 400 and 1000 can filter the air in my small shop up to 25 times per hour to about MERV 15-16. The Powermatic increases that filtering capacity by about 25-30% but does not filter the very fine dust as well. The photos show some the plenums under construction and the plenums and filters mounted as well as a shot of the bottom of the Wynn filter with removable Lexan piece allowing monitoring of the condition of the filter and, when removed, vacuuming of the filter during cleaning.
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[Frank Pratt]

Given that you have bronchitis, you should be aware the the MERV 15 Wynn filters are not HEPA. It's the smallest, submicron dust that does the most damage and a MERV 15 will let a lot more of it through than a HEPA will.

I have an air particle counter in my shop and with no tool activity, the <.3 micron count typically ranges from 50 - 200. A couple of days ago I was doing a little cleaning & organizing & the count was around 1200. Then I started the dust collector (with a HEPA filter) and cut up a bunch of MDF. Within about 5 minutes, it had dropped down to about 50. For the next hour of cutting on the table saw & rounding the edges on the router table, the count ranged from 7 to 27.

My counter doesn't do data logging, so I was only looking at the reading about every couple of minutes. It is placed at nose height, about 4' behind the table saw & router table. Clean air in a wood shop is definitely possible.

[Russ Webb]

I knew the Wynn was not HEPA. The only HEPA filters I could find were from Oneida. I debated with myself but decided to give Wynn a try because of all the favorable comments I’ve seen, because folks with ClearVue systems and Wynn filters seem satisfied, and because the comparable size Oneida filter was only 95 sq ft of filtration area compared to 230 sq ft for the Wynn. Having now directly compared the two brands I think the small Oneida filter is the better quality filter.

A particle counter is definitely on my list as it seems the only objective way to determine how much good these filters do and see if the Oneida HEPA really does a better job on the very small particles. It would also tell me when I should be wearing a respirator while in the shop and when I might be OK without one.

You must have a great dust collection setup. What system are you using?

[Frank Pratt]

It's an Oneida V5000. I ran a 8" main trunk because there are some extra elbows & distance to get to the DC, which is in another room. I went a little overboard with everything, but it worked out really well.

[Andy D Jones]

One thing to remember in assessing needed filter efficiency is whether the filter gets "one shot" at the dust (as in a dust collector), or multiple passes (as in an ambient air filter). Thus, the need for single-pass HEPA efficiency may not be as critical in an AAF as it is in a DC.

However there is another side to the situation. If a non-HEPA AAF needs so many passes to achieve HEPA cleaning efficiency, that the dust is instead "filtered" by your lungs, or to settle out on surfaces until it is disturbed again, then better single-pass efficiency and/or more airflow through the filter, or more AAFs, are needed.

-- Andy - Arlington TX

[David Walser]

Stumpy Nubs published a video showing how to do this in 2015. It contains a lot of good information for those who'd like to increase the performance of their ambient air filter. Russ' version, with it's custom made parts, may have better air flow than Stumpy's. Stumpy's version has the advantage of using off-the-shelf parts.

Here's a link to the video: https://www.youtube.com/watch?v=iR6P...kwq7kS&index=3

[Russ Webb]

Stumpy’s video was absolutely my inspiration and gave me both great ideas and the confidence that I could improve beyond what I had. I considered off-the-shelf parts as Stumpy did but decided that it wouldn’t be that much effort to build custom plenums that would give me better air flow with less turbulence. Most importantly, mine had to hang off the back of the ambient filters because I don’t have the floor space Stumpy has. I think my version does what I wanted and needed but Stumpy gets all the credit for the original idea.

[David L Morse]

I may have missed it doing a quick scan of the video, but I didn't see any performance testing. So, did it improve anything? I didn't see any evidence of that.

A proper figure of merit for an ambient air cleaner is CFM x Filter Efficiency. 800 CFM through a 50% filter has exactly the same performance as 400 CFM passed through a HEPA filter. There's an industry standard for this, AHAM AC-1. One of the outputs of the testing specified there is Clean Air Delivery Rate (CADR). CADR is determined by measuring the decay rate of the concentration of various types of particles.

If you have a particle counter you can make a similar measurement. It's the best way available to a hobbyist. Lacking that, Stumpy at the least could have measured motor current and gotten an indication of whether or not he had increased airflow.

[David Walser]

David -- You didn't miss anything in the video. He didn't provide a before and after CFM (or other performance) measurement. In his defense, he was replacing the internal filter, rated MERV 14, with an external filter rated MERV 15. The external filter is about 5x larger, in terms of square feet of filter media. And, the external filter can be cleaned several times before it needs to be replaced. The internal filters are disposable. So, Stumpy's argument was that the 'upgrade' provided the following benefits: cleaner air (because of the higher MERV rating), longer time between filter change/cleaning, reduced cost over time. He WASN'T promising more CFM of clean air. The cost of the upgrade was greater upfront expense (the current external filter price is about $200, while the internal filters cost $70 for a two-pack), the hassle of making the upgrade, and the extra room the ambient filter will claim after the upgrade.

Obviously, Stumpy didn't prove that his upgrade provides any of the claimed benefits. That could only be done with careful testing over time. Do disagree that it is probable that his upgrade will provide the claimed benefits?

[David L Morse]

...Do disagree that it is probable that his upgrade will provide the claimed benefits?

It's possible that the upgrade will provide some of the claimed benefits but I wouldn't say probable.

cleaner air (because of the higher MERV rating)

Really depends upon what happens to the actual CFM. The Wynn filter possibly has less pressure drop but there's the added pressure loss from the contraction getting to the filter. For particles between .3 and 1 micron the difference between MERV 14 and 15 might be about 80% versus 90% efficiency. If there's no change in CFM then the cleanliness level achieved by the MERV 15 in 30 minutes might take the MERV 14 about 4 minutes longer. CFM differences will, of course, affect this.

longer time between filter change/cleaning

Agree.

reduced cost over time

Maybe. Return On Investment will depend strongly on how fast you fill the filters.

I will say that Russ's implementation has a better chance than Stumpy's of getting those benefits because of the lower loss connection he's made to the filter.