Collecting *really fine* dust?

[HDRW]

Hi folks, I'm new here!

I have a problem:  My loft has incredibly fine dust inbetween the joists, and while boarding it over I've been using a Dyson DC07 (with HEPA filter) to clean out this dust.  I just don't like the idea of leaving it there "out of  sight"! 

I think it may be soot from when coal fires were a thing (this house was built in 1937 with 4 open fires) although it's grey rather than "as black as soot".  If it's not soot then I have no idea what it is!

Anyway, it's so fine that the washsable pre-motor filter and the HEPA post-motor filters clog up in about half an hour, so I spend more time washing the one filter and replacing the other (expensive!) than actually sucking up the dust.  Also, some of it makes it all the way through and shows deposits around the air-exit, so I'm probably breathing some of it too - a Bad Thing.

So:  I thought of getting a cyclone and putting in a first stage to catch the stuff before the Dyson gets it - and then found out about the Thien baffle.

My question, then, is which would be better at collecting this stuff?  I can get a cyclone for about £15 from eBay, and I have a bucket I can use for collection, but all the "shoot outs" I've seen are testing with woodworking equipment, so (probably) don't have anything as fine as my problem stuff.

Thoughts, please?

Cheers,
Howard

[tommitytomtom]

Regarding a sawdust collector or cyclone vacuum, the HEPA filters are likely going to catch some of the "fines" depending on how well they filter. Wynn Environmental makes large scale filters that are adaptable to sawdust collectors and are going to get even more of those' fine" particles. Another way would be to exhaust the fines through a sealed port to the exterior of your building although you'll most likely need to replace the air being exhausted by some type of filtered inlet from outside. Basically "out with bad air and in with the good".

[DustySanders]

The Thien Baffle systems we mostly deal with on this site are best suited for larger dust, which is why most of the systems here end up with the Wynn Environmental filters tomittytomtom refers to. If you built a small Thien style separator and powered it with your Dyson, you might end up with longer intervals between filter cleanings because less of the coarser dust would get caught in the filter. That is assuming there is any coarser dust in what you are vacuuming.

If you were to make a baffle separator for this specific task, I think you could increase your odds of sucess by designing it with a very narrow drop slot.

I commend you for wanting to get that nasty stuff out of your loft, but wonder if carefully stapling down some Tyvek or similar vapor permeable membrane before you put down your flooring might not end up being an easier and effective solution.

[HDRW]

Thanks for the advice, guys.  Unfortunately Wynn filters don't seem to be available on this side of the pond (we don't really have AirCon the way you do Over There, so I assume there isn't the market here).  I don't like the idea of exhausting the dust to the outside and I think my neighbours would agree!  :-)

The "thin slot" Thien baffle sounds like it's worth trying, although I don't understand the aerodynamics of it, I'll see how it works.  Has anyone tried making a variable-width slot, or a tapered-width one, I wonder?

Thanks again!

Cheers,
Howard

[HDRW]

Oh, and as for "sweeping it under the carpet", I'm more worried about it getting down into the rooms below than up into the loft. 

Many years ago my sister's bedroom ceiling fell down, and the biggest problem was all the dust and crud that had been sitting on top of it (the house was built in 1837, a hundred years before this one) and my father had to dress up like Neil Armstrong to clear it all out before repairs could commence.

So while it's tempting to leave it there, it just doesn't feel right to do so.

Cheers,

Howard

[cantfigureausername]

A Dyson is ridiculously small to fight fine dust as you've described. This will not work, whether or not you add a cyclone to it.

Also, a Dyson is in my personal opinion a pathetic vacuum which is more designed to fool people with snake oil than to actually work. It has cyclone magic powers with a total of 14 "cyclones". Only just, the design doesn't look like these will actually do any separation at all (air blowing straight down into them at an angle that actually cannot conceptually work). The only really good thing about the Dyson is its HEPA filter.

For your problem, you will need a much bigger (10-20 times) airflow than anything the Dyson will produce. And you will need a professional to figure out the very non-trivial problem of getting the flow exactly right. Because, you know, more is always better, but more is not always better. More airflow will eliminate dust better, but at some point, the airflow itself impacts quality of life. Also, getting the right suck/flow without a noise level that will drive you insane is a very non-trivial problem.

As for a cyclone, this can be used to pre-separate coarse and some of the fine dust, enhancing the HEPA filter's performance and lifetime. But you will need a HEPA filter in any case, too. Also, you will need something that "sucks" the right way. Vacuum cleaners and shop vacs are usually built to provide a significant pressure gradient because you may need to suck in bigger stuff which is lying on the floor, and that just doesn't work otherwise.
Dust collection and even moreso air purification doesn't need to suck up large particles so urgently, but it needs a high air volume (the CFM figure is primarily what one needs to look at, the pressure is not that much important, although of course you must be aware of pressure loss due to ducting and the cyclone). After all, what it does is filter out particles that are light enough to be in the air on their own already.

Cyclones isolate larger particles (such as PM10 and up) much better than smaller ones. Unluckily, it is not the large particles that we are usually interested in as they tend to eventually fall to the ground anyway, they're easy to cope with, too, and not a health issue (your nose, if nothing else, filters them). It's the smaller ones (PM2.5 and PM1) that we worry about.

Depending on the build and on the load, you can expect a no-crap cyclone to remove anywhere from 80% to 95% of the particles that we are mostly interested in. For PM1 and below it's much less (like 50%), but luckily, to our advantage, there is not so much of these in the air, comparatively. So, overall, we get out with 80-95% in the range that is important to separate. That's enough to enhance your filter's lifetime, but it is not enough to be considered "safe, problem solved".
For that, we  want a 5-sigma or 6-sigma reduction, and for this you will need to use a HEPA filter after the cyclone. There is no other way. Even then, most affordable HEPA filters will only achieve 6-sigma for the combined range, for very small stuff they often only achieve 98-99%, too (or worse). There's unluckily some legal leeway in the test procedures, too, so even what's printed on the filter is usually only 95-99% truth and 1-5% lie. But, that's as good as it gets.

The most important technical term for what you are interested in for the cyclone is called "cut point", that's the size of particles of which 50% get separated (anything larger gets separated as well). In the end, you want more than 50% of course, but research uses that figure, so what we are looking into is "pushing down the cut point" in order to actually push the total amount of stuff that we don't want closer to zero.

Things that affect the cut point are, among others:

• the load (so e.g. in the shop where you have kilograms of particulate matter in the hose, it makes a lot of sense to add a pre-separator)
• the speed of airflow (more is better)
• the cyclone's diameter (more is worse)
• the cyclone's length (more is better, but only up to some point because of pressure loss)
• the size of the outlet relative to diameter (less is better)
• the size and geometric proportions of the inlet (smaller and slimmer is better, a 7/5 ratio being considered the optimum)
• the angle, if any, of the inlet (for example Pentz cyclones achieve higher separation due to the explicit downwards lead-in)

What works quite well (70+ years of use in industry and agriculture) for fine particles is what's called 2D2D or 1D3D style separators. These are cyclones where the upper, straight bit is either equal to (1D...) or twice (2D...) the diameter in length, and the tapered bit is either twice (...2D) or three times (...3D) the diameter, the 1D3D separator being only marginally better alone, but significantly better in series. There's an awful lot of mostly-Chinese research on the topic with chaining 2D2D-1D3D appearing to be the best performer.