Exhausted Air Recycling System

April 22, 2007 10:05 AM

Australian inventor Chris Bosua, frustrated by the inefficiency of his air compressor, devised a method of recycling the exhaust air from air tools. His Exhausted Air Recycling System (E.A.R.S.) improves efficiency by eighty percent. It runs cooler, almost halves the power consumption, extends the life of the compressor, provides a cleaner working environment, and reduces the noise of an air tool to that of a sewing machine. Happy Earth Day, everyone!
posted by weapons-grade pandemonium (31 comments total)

Isn't this just really a sort of turbocharger? I realise there are differences, but it's interesting that you can patent something based on the fact that it's used in only a slightly different way. Good stuff in any case.
posted by jimmythefish at 10:29 AM on April 22, 2007

Sometimes the simplest solutions are the most elegant yet most elusive. Nice job my Bosua.
posted by caddis at 10:33 AM on April 22, 2007

Nice invention. His website.

Is the Google logo melting by the hour?

Would like to see routine rainwater harvesting.

Some other green inventions.

An excellent green inventions wiki, LiveGreenOrDie.com
posted by nickyskye at 10:33 AM on April 22, 2007 [1 favorite]

Thanks, nickyskye. I was hoping my post would precipitate more Earthy links.
posted by weapons-grade pandemonium at 10:40 AM on April 22, 2007

If pressurized air gets 'greener', wider adoption of dry ice 'blasting' might offset gains ... someone get the solar calculator
posted by acro at 10:47 AM on April 22, 2007

Chinese company tops Greenpeace "Green Ranking" of electronics industry --
Apple still bottom of the barrel
"Given the growing mountains of e-waste in China - both imported and domestically generated – it is heartening to see a Chinese company taking the lead, and assuming responsibility at least for its own branded waste," said Iza Kruszewska, our International Toxics Campaigner, "The challenge for the industry now is to see who will actually place greener products on the market."


Lenovo, which bought IBM's consumer electronics division in 2005, scores top marks on its e-waste policies and practice; the company offers takeback and recycling in all the countries where its products are sold. Lenovo also reports the amount of e-waste it recycles as a percentage of its sales. However, the company has yet to put on the market products that are free of the worst chemicals.

Other companies in the top five include Nokia (2nd), Sony Ericsson (3rd) Dell (4th) and Samsung (5th).

posted by acro at 10:55 AM on April 22, 2007

Bear in mind, acro, that it's recycling pressurized air that's greener--running a turbine and routing the air back to the compressor rather than venting it into the environment. Sandblasting or dry ice blasting would not easily permit recycling, since it depends on the vented air to carry the abrasive particles. You shouldn't avoid being green simply because someone is offsetting you. I must admit, though, every time I compost a teabag I imagine how many it would take to offset David Suzuki flying from Vancouver to Toronto and back again dozens of times a year.
posted by weapons-grade pandemonium at 11:15 AM on April 22, 2007

A blog (last couple days ?via mefi) had some (disturbing) pictures of vermicomposting... google 'red wiggler + kitchen'
posted by acro at 11:47 AM on April 22, 2007

Hmm, it's hard to tell from his site but I am wary about the efficacy of his invention. It sounds like jimmythefish is right, that his invention is a turbocharger of sorts (more likely an air-booster). If so, I'm VERY skeptical of his "80% improvement" figure.

The power of a turbine is related to the difference in inlet & outlet pressures, and the flow rate. We can increase the power by lowering the exhaust pressure closer to atmosphere (which is effectively what this invention seems to do). Unfortunately, as the air pressure is lowered, it expands, so we have to build a proportionately larger turbine to keep up the same flow rate. Moreover, as we bring lower the outlet pressure, the incremental increase in power is offset by the friction on the growing turbine's seals (doubly so if he's using the extra energy run a second compressor). Presumably air tool manufacturers choose their outlet pressure at a point where most of the useful energy is captured, without making the tool cumbersome. I would be shocked if that point left 80% of the power going out the exhaust.

The lack of product pictures on his site is also fishy. I'll bet donuts this guy is another "save the earth with my product" snake-oil salesman / VC hunter. If he's is so concerned with the energy his compressor wastes (fluid power is inherently wasteful), why doesn't he use electric tools?
posted by Popular Ethics at 12:13 PM on April 22, 2007 [1 favorite]

From the file: Out-there technologies to 'save the western consumer society': How about a superconductor-based electrical grid... If you have a cheap/clean point source of electrical power, you need a way to transmit it great distances (e.g. for desert-solar... ocean-wind turbines... etc.)
posted by acro at 12:20 PM on April 22, 2007

... motors based on the same technology (High-Temperature-Superconductors) are being developed for ship use ~"36 MW motors"
posted by acro at 12:23 PM on April 22, 2007

OK, I dug a little deeper into the site (which is lacking in useful information). He isn't adding a turbocharger, he's just returning the exhaust air from the tool back to the main compressor's inlet, making a closed-loop system. That makes slightly more sense except:

1) the extra work pumping the exhaust air to the compressor will reduce the benefit of the system somewhat
2) You could accomplish the same thing as I said previously - by exhausting close to atmosphere, the room would become your return pipe. This is not done because for reason's I've mentioned.
3) Now your tools have to connect to big-ass return hoses as well as supply hoses (they would have to be large to reduce friction at low pressures, they needn't be very heavy though). This is making electric tools look better all the time.

So it's snake-oil with a modicum of technical sense. Let's call it fish-oil (love those omega-3s).
posted by Popular Ethics at 12:27 PM on April 22, 2007

I should note that the other benefits he touts - reduced noise, drier air, reduced emissions, do have some value. I'm sure he'll do really well too, because if you want an E.A.R.S. system, you'll need a new E.A.R.S compressor, E.A.R.S hoses & fittings (instead of standards), and all new E.A.R.S. tools (or at least retrofits). It's a smart (if slightly deceitful) business.
posted by Popular Ethics at 12:37 PM on April 22, 2007

A 'trusted tools' business model, since you wouldn't want a contaminated return line to the compressor...
posted by acro at 12:43 PM on April 22, 2007

Help Roots tackle the problem of climate change!
posted by acro at 2:02 PM on April 22, 2007

The power output of a tool increases with pressure difference. This design uses some of the pressure difference to run the return system. It seems to be similar to multi stage steam engines, in a way.

In multistage steam engines you have two or three cascaded cylinders, each cylinder designed to run at lower pressure than the one before. The first cylinder alone could produce more power than it does, if you allowed it to make use of the full pressure differential between boiler and atmospheric pressure. However, if you pass some of the pressure along to a cylinder that is tuned for a different operating range, you get more power (and therefor efficiency) overall, by using multiple stages.

So, his approach is probably sound, although it will reduce the power output of the tools a little. Hard to justify a big expenditure on it though, I'd think - all that extra hose, and modifications, probably can't pay for themselves on energy savings.
Not that I know much about air tools..
posted by Chuckles at 2:16 PM on April 22, 2007

Popular Ethics, the return hoses on the main E.A.R.S. site look to be the same diameter as the supply hose. The main site has several product pictures. Also check out the product catalog.
posted by zsazsa at 5:51 PM on April 22, 2007

Another site for various e.a.r.s. products: exhibit 4. the e.a.r.s. chainsaw
posted by acro at 6:10 PM on April 22, 2007

zsazsa: the return hoses on the main E.A.R.S. site look to be the same diameter as the supply hose

So it appears! Now I'm even less sure they're saving much energy. Exhaust air is much less dense than supply air so you have to move more volume of exhaust per second to pass the same amount of mass. Thus in identically sized hoses, the exhaust air must travel much faster than the supply air to maintain the same flow. Unfortunately friction scales by the square of velocity, so the exhaust hose would lose a disproportionately high amount of energy to heat.

I would be very surprised if the typical air tool exhausted at a pressure high enough to pump the air back to the compressor in a small hose and still yield 80% more energy.
posted by Popular Ethics at 6:50 PM on April 22, 2007

The person who says it can't be done shouldn't interrupt the person who is doing it.
posted by TheNewWazoo at 9:00 PM on April 22, 2007

The person who says it can't be done shouldn't interrupt the person who is doing it.

Well, sure, but what we're wondering here is whether the EARS guy actually is doing it, or whether (like a few previous New Inventors stars) he's a scam artist. It'd be quite easy to test the claims made for the system, and most air tools certainly are much less efficient than electric ones, but it's been quite a while since the device was first on the show, now, and no independent tests seem to have been done. The Technical Data section of the EARS site is at the moment, shall we say, a little sparse.

See, for a previous example of lax New Inventors fact chekcing, the Greenfire magic emissions-reducing spark plugs. Which appear to have sunk without trace, after greatly exciting the New Inventors judges.

See also the Antibio water purification system, which won The New Inventors the Australian Skeptics' Bent Spoon Award for 2004.
posted by dansdata at 9:58 PM on April 22, 2007

Not going to comment on the physics of it (I've been pulling my hair out over a group physics assignment all weekend!), but I will say that the mechanics of such a system - the need for return air hoses, etc - is much more feasible in a commercial workshop than in a home garage. Think places that already have air loops, centralised dust/fume extraction, etc.

In fact, there are already places that use a similar 2-hose system - not for any benefit from the returned air, but for noise reduction (venting the exhaust air though an external central baffle/damper).
posted by Pinback at 3:03 AM on April 23, 2007

1) the extra work pumping the exhaust air to the compressor will reduce the benefit of the system somewhat

There is no pumping, just flowing due to pressure differential. The exhaust air is already at higher pressure than atmosphere. Do you really think the pressure drop through the lines is a significant energy loss? I doubt it.

2) You could accomplish the same thing as I said previously - by exhausting close to atmosphere, the room would become your return pipe.

You just wasted all the energy in that pressurized exhaust air. Oops.

3) Now your tools have to connect to big-ass return hoses as well as supply hoses (they would have to be large to reduce friction at low pressures, they needn't be very heavy though). This is making electric tools look better all the time.

Again, I doubt there is even a significant pressure drop through those lines. The quantity of air is not that high (an impact wrench might use 8cfm at 90psi), just the pressure. At most I would expect a few psi loss.

If you want to be skeptical, I would look to Chuckles answer.
posted by caddis at 8:04 AM on April 23, 2007

we're wondering here is whether the EARS guy actually is doing it, or whether (like a few previous New Inventors stars) he's a scam artist.

Quite right. These kinds of claims merit particular skepticism because they promise to absolve all your polluting sins with just a simple payment (like new spark plugs), so you don't have to make a more substantial change (like driving less).
posted by Popular Ethics at 8:10 AM on April 23, 2007

Paging asavage. We may have Mythbusters material here.
posted by weapons-grade pandemonium at 8:59 AM on April 23, 2007

1) There is no pumping, just flowing due to pressure differential. The exhaust air is already at higher pressure than atmosphere. Do you really think the pressure drop through the lines is a significant energy loss? I doubt it.

Of course I do. The compressor has to pump the air back to it's inlet. When you try to pipe the exhaust back to the compressor in a small tube, there's going to be an extra pressure drop which will reduce the flow rate, reduce the tool's power output, and reduce the potential energy savings

2) You just wasted all the energy in that pressurized exhaust air. Oops.

Que? You wouldn't waste any energy if the exhaust air weren't pressurized (ie, the tool exhausted at close to atmosphere). Doing so would make for a rather big turbine though, and, as I mentioned before, I doubt there's that much energy to recover.


3) Again, I doubt there is even a significant pressure drop through those lines. The quantity of air is not that high (an impact wrench might use 8cfm at 90psi), just the pressure. At most I would expect a few psi loss.

Remember that air is compressible, and the actual flow rate is a function of pressure. 8scfm is only 1.90
cfm at 90psi, so the supply air velocity is only be about 58 ft/s in a 1/4 inch supply hose, and we'd lose about 4.5 psi to friction. But at 10psi, 8scfm is equivalent to 5cfm, so the exhaust air velocity is actually 246 ft/s, and the exhaust hose would lose a whopping 80 psi! In reality, the flow rate would drop until the total pressure matched what the compressor could manage, and the tool would consequently lose power.

I'm not denying that the compressor will use a little less energy when you close the loop, but I doubt the effect would be so dramatic. To that end, a design which doesn't increase the hose size for low pressure flow makes my engineering sense tingle.
posted by Popular Ethics at 9:04 AM on April 23, 2007

I assumed a 20ft long hose for the above calcs. I'll post the source in just a sec...
posted by Popular Ethics at 9:09 AM on April 23, 2007

OK, I goofed a bit with my calcs. The pressure drop formula has a term for density which partially (only partially) makes up for the squared velocity term, so the results don't look quite so bad.

The corrected calculations show a pressure drop of 4.4 psi on the supply (sounds about right), and 13 psi on the exhaust. That means that the tool exhaust pressure has to be about 13psi (More if the piping is longer than 20ft) just to overcome the return piping losses (without any energy savings at the compressor inlet). If you want any energy reduction, the tool exhaust has to be higher yet. I haven't measured any air tools, but like I said, I would be surprised if they left that much pressure unused at the exhaust.

y'all are welcome to check my formulas & assumptions. I'd love to learn if I was wrong.
posted by Popular Ethics at 10:07 AM on April 23, 2007

Popular Ethics, I think your calcs are off. 8cfm at 90 psi and 70 F is about 4 lbs/min. Assuming no leaking, that same amount of air at 10 psi is about 24 cfm (horrible rounding here). Anyway, using the Darcy formula and assuming smooth pipe, and less rounding, I got about a 30 psi loss for a 1/4 id hose, not 80 psi. This is still significant, but at 1/2 inch id it drops to a little over 1 psi loss, which is insignificant. (What a waste of 30 minutes)
posted by caddis at 10:19 AM on April 23, 2007

caddis: yep, I caught that error - 30psi is much more reasonable (I got 13, but you'd have to check my assumptions to see why the difference). A 1/2" hose would reduce the losses considerably, but looking through the website, it looks like he sells 1/4" hose for both inlet and outlet. That's why I'm skeptical - why wouldn't he supply larger exhaust hose if he was trying to reduce energy losses?

Thanks for your 30 minutes though.
posted by Popular Ethics at 10:52 AM on April 23, 2007

There's more discussion on the ABC's dreadful old "guestbook" discussion board, including posts from someone who says he's been talking to the EARS inventor. Who has not been saying anything very reassuring.

(See also this page.)

The basic point of contention here seems pretty straightforward - is it in fact possible to harvest significant energy by any means from the exhaust of an air tool, without reducing that tool's power?

It seems quite obvious that this is not, in fact, possible. By definition, any turbine or return hose or triple expansion engine or whatever hanging off the exhaust port of the tool will create back pressure, which will reduce the pressure differential across the tool, which will reduce the tool's power.

Adding back pressure to a tool certainly will reduce its air consumption, and therefore reduce the amount of power consumed by the air compressor that's feeding it. Plug the exhaust of the tool completely and the compressor will only run long enough to pump up its reservoir, then stop forever, giving from that point on a 100% "efficiency gain", if all you care about is power consumed and not work done.

So I suppose it actually is possible that the EARS system reduces power consumption by some impressive amount. It seems that it does this by reducing the power of whatever tools you use it with by the same amount, though. Only if your tools are overpowered in the first place will this be of benefit.

(If that's the case, you should of course just be turning down the pressure of your compressor, or using flow restrictors in-line with whichever of your tools are overpowered, not adding more hoses.)
posted by dansdata at 6:22 PM on April 23, 2007