Having compressed air available in a workshop can be extremely useful. Having a compressor isn’t such a pleasure though, because unless it’s a very expensive model, it will be one of the noisier devices you own. Other than putting your compressor outside, is there a solution to the noisy side of having an air line? [Dominik Meffert] may have found one for his CNC plasma cutter in the shape of a rack of much quieter fridge compressors arranged in parallel with an air tank.
Of course, there’s nothing new about using a fridge compressor in the workshop. Indeed, such units are even commercially available as compressors for low-capacity tasks such as airbrushing. But we’ve never seen so many at once. It’s not entirely apparent how he’s handling the replacement of any lubricating oil that’s being caught in his filters, and we hope the refrigerant was disposed of safely, but we can see he’s on to something.
Fridge compressors have appeared here many times over the years, for more than compressing, we’ve even seen one as an engine. They aren’t always as strongly built as they should be though.
You can technically just buy these off the shelf with no refrigerant in them, typically marketed as replacement units or even buy them used for that matter. Do note that they have a HUGE amount of variety and are built in very different ways depending on things such as the intended market. Plus they have so many different product names for literally the exact same product. So be sure to check to see that what you order is what you are actually looking for.
The downside to that is you will then need to install everything yourself with the right equipment and refrigerant, etc. It’s not THAT hard but you must both have or use moderately expensive equipment and also follow certain requirements such as very well vacuuming everything, etc. Some of the refrigerants used today are VERY FLAMMABLE. on top of not really being good for the environment and on top of that, starting to get pretty expensive as well. Class 3, Class 2 and Class 2L refrigerants are all flammable. R32, R290 and R600a are a potential hazard.
The other part here is that compressor tank looks to be super harbor freight like. Owned one many years ago. DO NOT RECOMMEND. Not sure what the maximum pressure this unit can generate in total (seems like 6 bars or about 87 PSI) but at least they seem to have installed a pressure release valve. Of all the things to skimp out on, that and a quality compressor tank are not things to save a few bucks on.
Cannot tell electrically here but these do use a good bit of wattage so keep that in mind as well. They can also get quite warm if they run a fair bit. Says about 2 minutes and 15 seconds to top off the tank from presumably empty.
What about CFM numbers here? Why so many units in parallel specifically? Lower runtimes? How much power do they draw when running? How is that compared to your average (to be fair typically quite loud) compressors?
Agree here as well with respect to filters. No idea how they are lubricating this but presumably it was added in when they properly installed them in parallel?
What if one unit fails or needs to have additional units added?
Lastly, every compressor differs in the amount of pressure they can generate and some newer ones can produce way more than 150 PSI or so. Looking at you, R410-A. What is the pressure output here and what is the maximum rating of the plastic tubing being used? How well can they actually seal compared to welded copper? How resilient is the plastic tubing chemically to the refrigerant / lubricant?
Interesting idea and in no way an expert here so if anybody has anything else to share, please let us know!
the article’s point was not using them as refrigerant compressors at all, but General Purpose…
It does not seem like their intention was that suddenly they were expecting to still use them as refrigerant compressors? They still need lubrication to run (for periods of time) though and air compresses and fluids don’t (nearly as much anyway). These generate heat when ran but typically have large cooling units attached. These no longer do as one example.
An average HVAC compressor is designed to take in a liquid and output gas in a closed loop. This build is taking in a compressible gas and outputting a compressible gas that is then used to fill a compressor tank.
Not pointless and certainly a hack which is sort of the point here but what does that change is the question and more over what else, if anything, needs to be considered in the build? Simply because you remove a part doesn’t mean you cannot use it elsewhere or for other uses but one should at least be aware of the fact that it had an original design intention and tried to work around those limitations in the traditional use case (HVAC here).
Here is a very basic traditional HVAC compressor. You basically pull the compressor out and go from there. The question is not are they doing that or not. The question(s) are what does that mean exactly for actual use in this manner?
Refrigeration compressors can’t draw liquid refrigerant. Liquid is non compressible and would break the compressor in short order. They draw vapour only. These hermetic compressors contain their own oil much like an air compressor does and oil return can be done very easily. Only issue with oil is the type used in the compressor from the factory. Many come charged with POE oils. These oils suck up moisture like a sponge and could cause issues.
There is no refrigerant contained in a replacement compressor.
Most manufacturers have switched to PVE oil because of extensive problems with POE.
https://www.achrnews.com/articles/113478-adoption-of-pve-oil-for-r-410a-applications
In school we put some POE into a beaker and watched for a week as it turned cloudy with water vapor inside of an air conditioned classroom. We tried to get all of the water out and return it back to clear by vacuuming and heating it for a month before we gave up. Made a lasting impression on me to keep that stuff sealed up as much as possible. I threw cans of oil away after opening them, no installs in the rain, etc.
I doubt that this installation will have problems, he’s not pushing these things anywhere close to the designed pressure.
Well this shows you are not a hvacr service tech. An average HVAC compressor takes in a low pressure low temperature gas and outputs a high pressure high temperature gas. Then the condenser removes the heat and turns it into a high pressure liquid to supply the Thermal expansion valve or piston type metering device to a larger line in the Evaporator coil dropping the pressure and temperature to collect heat out of the air to then move it as a low pressure gas back to the compressor to restart the cycle. If you are getting liquid back to the compressor it is over charged and will cause premature failure.
I dont think you understand what’s going on here after reading your comments. The ac compressor doesn’t take in a liquid and output a gas. This is nothing new and has been done to death. The only unusual part is running this many in parallel. If you want to learn more about the details just Google DIY silent compressor.
“An average HVAC compressor is designed to take in a liquid and output gas in a closed loop.”
No. No no no no no. They hammer this into HVAC techs during apprenticeships. HVAC compressors are designed to receive and discharge *vapor* refrigerant only. Liquid refrigerant getting to the compressor is called floodback and it will damage then break a compressor.
You’re right that running HVAC compressors without refrigerant is a bad idea though. The refrigerant both cools the compressor and carries oil to it. I would imagine HVAC compressors used to compress air would quickly cut out on thermal overload.
Of course you have to replace the lost oil from time to time but otherwise this works just fine
Wrong. HVAC compressor intake vapor and discharge hot, high pressure vapor. Liquid refrigerant can and will IMMEDIATELY destroy reciprocating hermetic compressors such as these. HVACR professional here.
It throws out high amounts of oil and some refrigeration oils are hygroscopic. But you can change it use plain old mineral oil if you only compress air and do not need (or have) the closed oil return circuit. The latter is the reason for more exotic oils for the new chlorine free refrigerants.
I have never seen someone so incompetent in information. So many wrong things. From run times to pressures to just how things work. I really recommend looking into things before typing on your keyboard. If any of the compressors were r410 rated, you see a max pressure of 450psig and operating pressures into the 300s all day long. I dont even have the hours it would take to type out all of the issues with your post.
That all seems sound but they’re compressing air so…
I don’t understand your post at all. Did you just want to vent your wonderful knowledge completely unrelated to the article itself? The article is about using them NOT in their intended way, hence it is a hack for a HaD article.
I don’t think anybody is discounting the use that is other than the “intended” use. Seems like it is more about what differences that would possibly create or potential issues it might cause? There is a reason you don’t fly aircraft with auto parts.
aircraft need a little more safty. A defective compressor just seizes to function. This is not life threatening in any way and for a medical ventilator it is not suitable anyway. :-) Too much oil throw.
You might not fly aircraft with automotive parts, but plenty of people with experimental aircraft do. Chevy ls to snowmobile engines. Pretty much if the power to weight ratio is there someone will try it!
Best way to hide noisy machines is to dig a shallow trench, wide enough for the device, with room to service and provide airflow, and then surround it with a double-stacked overlapping wall of sandbags, about 2 foot higher than the machine. This directs the sound upwards.
I think you’re missed the point a little here – the purpose is a much quieter source of compressed air, and yes fridge compressors have a very low CFM compared to the average air compressor hence many units in parallel – you can see the same approach in commercial/industrial “silent” units such as Clarke’s “Shhhh air” compressors that mount 3-4 units on top of a tank where traditionally there’d be one big motor and one big compressor.
Overall efficiency will be lower, although running current should be low-ish the startup kicks could add up massively unless the starts/stops are staggered across the units.
If start/stop is a problem, you may switch the compressors on and off in a cyclic pattern. This also enables variation in airflow while distributing the runtime equally across the compressors in the long run (I dare to mention an earlier comment on this in a different context: hackaday.com/2022/07/25/a-simple-charging-station-for-twelve-powerbanks/#comment-6497242)
Those plastic lines are often rated over 10 bar (~145 psi) and are used in many industrial applications. They’re very cheap, easy, and also compliant (they do not harden and break when bent). If that tank is a harbor freight 7 gallon, it is rated at 160 psi. This is a really interesting idea man, it seems safe to me, especially considering that each compressor is isolated with a solenoid valve.
Depends on the line in question, I’ve used plastic line like that in paintball guns to carry unregulated CO2, so that’s up to 1200ish psi in the summer.
I wonder about vastly superior reliability. Everyone I know it seems has at least one normal one, but 2 total out of them all I know about actually work. This ongoing fact has me mused them as being the desktop inkjet printer (least reliable device in every home) of the garage. While how many times have to had your fridge compressor go out on you?
Moisture coming in thru the intake(s), where they’re not designed for it, however…
You get what you pay for really. Being able to buy a 120psi compressor for $200 and have it work for five years without maintenance is really a miracle in its own right. There is a reason the bottom end commercial compressors from Ingersoll or any other reputable brand costs $2000 and has a six month rotating maintenance schedule.
Not sure you understand what’s going on here. It’s for compressed air, not refrigerant.
Well to make things easy just run over to Home Depot grab 2 sheets of plywood and 2 sheet panels of the styrofoam insulation. Build a box around your compressor and on one wall leave a 2 inch gap where the corner to corner joins then place another wall 2 inches in from the wall that has the gap and on this wall leave a 2 inch gap but on the opposite side of previous wall. In all 4 total is really quite cause the maze design is just like the baffles in a muffler<— that are made of metal. Just imagine how quiet this works!. It's fantastic..
How hot does your compressor get inside that box? Otherwise, sounds pretty good. (pun intended)
I have no idea why you are talking about refrigerants when the guy is compressing air? These compressors are partly submerged in oil so in a world were we don’t want oil in our air supply a bad start. Multiple compressors like this installation will probably cause start up issues, they draw large currents on start up so multiple units will compound the problem unless some very fancy staggered start up system is designed. The cost of new compressors Is not cheap so again multiple compressors equates to expensive system build costs. Other than noise there isn’t a decent reason to waste time and effort farting about wasting money on a system like this. As far as handling refrigerants go you not only should be trained and qualified to do so but should be recovering them in a safe manner for disposal.
R290 and R600(a) are plain old propane and butane. Yes, highly flammable but not really toxic. R32 is another thing, it is fluorinated and flammable, so a quite bad combination of properties, “worst of both” and when it burns really nasty toxic products come out.
I did similar with an old R12 freezer compressor >30 years ago. The tank was a connection of 3 2l PET coke bottles.
The power rating of this compressors is normally between 60 and 150W. Quite low flow rate but up to decent pressure. So it makes senso have many in parallel.
is possible uncompressed for creating liquid air?
convert air to liquid
Generally this is done by refrigeration. No matter how much you compress oxygen at room temperature it doesn’t become a liquid: its critical point is at about -110C or so, and above that, there’s no longer a phase boundary between gas and liquid.
Not without compression, and a LOT of it. Also, you probably won’t be able to reach the pressures needed for the task with anything off the shelf. For example the Linde process has a high side pressure of around 75 bar – https://en.wikipedia.org/wiki/Hampson%E2%80%93Linde_cycle
My (almost silent) Bambi appears to be basically a fridge compressor.
https://www.coleparmer.co.uk/i/jun-air-jun-air-oil-lubricated-piston-air-compressor-2-12-cfm-120-psi-4-l-tank-120v/1620203
I paid noting like that for it, though, and I have no idea why it would be 10x the price of an ostensibly similar Bambi.
Talking of Bambi, they put multiple units on one reservoir, but not quite to the level seen in the article referenced. It looks like they go up to three: https://bambi-air.co.uk/products/md-range-silent-air-compressors/
They wrote that the standard specification is very high; air receivers are internally powder coated to prevent corrosion, internal valves are stainless steel and each model is equipped with a 10 micron air filter & outlet pressure regulator as standard.
Maybe because they anticipate air with water inside (humidity) to corrode steel under pressure and heat? They probably also went with compressors that were designed or built more for this application specifically?
The only silent compressor fitted with piston rings eliminating oil carryover to the air supply part is interesting too.
Not sure the piston ring part initially makes sense. It’s a scroll compressor, right? It oscillates. So why add a piston ring?
Niche product for sure which is fine but still neat to see it being a commercial product and curious as to what they identified as needing to be addressed in the design phase.
2 cfm/ 2400 English pounds plus VAT?
That’s what? $3.50 in real money?
Must be a joke.
At least it isn’t made by Lucas.
And they only charge an extra 180 pounds for a five gallon air tank upgraded version.
What a bargain! English manufacturing is definitely poised for a comeback. We’ll all be broke down on the roadside soon.
Industrial screw compressors (similar to a roots type blower) are really quite and more efficient than piston types. They also cost a bunch more. Unless you’re painting cars or media blasting, payback time vs the noisy cheap version is long. Earplugs are cheap.
Maybe some year we will see the first DIY screw compressor. For now the tolerances required seem to be out of reach for hobbyists.
I’ve used a salvaged fridge compressor with a receiver from an old compressor in my workshop for about 30 years. I’ve found all the leaks, so it only runs when it has to. Has a pressure switch, of course, but an over pressure relief is absolutely vital – the compressor is capable of way over safe pressure! The compressor is in a cupboard and is virtually inaudible.
I let it suck in a bit of oil every few years, and I know how much comes out, because it appears in the filter/drier.
No home workshop is complete without compressed air!
Just a thought but would this work as a homebrew compressed air storage for a turbine/generator? Kind of a UPS ? Use solar/wind to charge a bunch of tanks ?
Nice cheap idea. I like it. But lot of energy will be lost in compression heat.
I have an 80 gal compressor at my shop. What I did was use some PVC pipe to run the intake outside. While it’s still a bit noisy, it’s significantly less so now.
I’m refurbishing an Ingersoll-Rand T20 right now so this is *really* encouraging… to *hear* ;)
Also, mankind sure you have proper pads under the feet dramatically cuts down on noise.
Great thanks for the article about my project :)
I replaced the original lubricant oil with 0W20 motor oil and added an oil level indicator to each compressor (I first tried normal compressor oil which caused starting problems because of its higher viscosity).
I got the compressors from broken fridges that got left behind by the campers after an electronic music festival. I only took compressors from fridges filled with R600a, where almost all of them were already empty of refrigerant.
I used 8 of them to fill the tank fast enough to keep up with the flow rate of the plasma cutter and also to prevent them from heating up too much. 50l is enough to keep them off for minutes while cutting and so they don’t heat up much when the entire cut takes only a few minutes.
Another option (still a bit pricey though) is a small medical compressor. Very quiet. But if you look around, you can find rotary compressors used, for not much more than a new conventional piston type compressor.
My mother worked as commercial artist for years, a lot of airbrushing was done. To stop compressor pulses from spoiling thee work, you need a huge tank. Or, more likely, wait until the tank is charged, and then work.
Compressors are noisy, and, the required pressure is pretty low.
So the solution they settled on, was a tractor inner tube. Filled, every couple of days at the local petrol station.