So, has anyone made a working autocascade yet? [Archive]

Charles Wirth

08-09-2016, 09:02 AM

I have a working autocascade with dual heads. The heads both have bypass valves so they can be controlled independently or both together.

It is running the polycold blend that was modified for higher capacity, not sure of exact blend. The compressor I think is 2 or 2.5hp 220v with excellent capacity @ -100c.

It originally came as a single head "Polycold" and it was modified by Chilly1 for dual linesets with blocks. They mount to all sockets so far.

After Chilly1 modified it he could not get gas blend correct and it was re charged by mytekcontrols iirc, I also think he worked for Polycold.

Thanks S7ev3n, the previous owner of the Polycold.

PCIce made an auto, I don't think it had much capacity but he did show that it worked.

http://www.xtremesystems.org/forums/member.php?42860-mytekcontrols

Check out his threads

aenigma

08-09-2016, 06:25 PM

Oh right on thanks for the reply FUGGER, nice to see someone I recognize from the good old days! That sounds like a beast, I'd love to have the equipment and refrigerants available to make something like that.

Being stuck with nitrous oxide is a pain, it's a pretty lousy 2nd stage refrigerant, but it's what I've been using since me and captaincascade were trying to see who would be the first to make the first working autocascade. I never did make a thread or post any pictures for some reason, just mentioned it in a few threads. I still have it around, but something heavy fell on it and bent a line which broke when I tried to straighten it, so it isn't charged, but it worked pretty good. Well, it did before I accidentally broke my CPEV and went to cap tube on the plate HX. It used to handle around 200-300w at maybe -80 or -90c, I can't remember. Coldest it got was about -102c i believe. It has a 1HP copeland that captaincascade sent me. These autocascades need a lot of compressor power.

I have a tandem compressor setup on the latest one I've been toying with with a small 1/3hp copeland from 1989 and some kind of old rotary compressor from a small window unit and it does about -90c on average. No idea of load capability since it's just a coiled 1/4" evap so I can chill a beer in a hurry lol

They're a headache to fine tune, but that's the fun part. When it's working right then it's boring haha.

Thanks again for the reply, I'll check his threads out, although it seems like none of the pictures work on xtreme anymore.

<edit> Oh yeah, I remember him starting that autocascade back after I made mine, it turned into quite a machine! Those guys work for polycold and with autocascades for a living, that's like cheating :P

zanzabar

08-09-2016, 07:35 PM

is that something we will see at IDF?

aenigma

08-09-2016, 08:49 PM

What is IDF?

zanzabar

08-09-2016, 09:07 PM

What is IDF?

intel developers forum. fugger goes every year and overclocks for them.

aenigma

08-09-2016, 09:19 PM

Ahh gotcha, very cool! I haven't done any serious overclocking in years. I'm still on an old P5K with an E8600 3.33 that I would occasionally overclock to something like 3.6 or 4, I can't remember, just a standard overclock though. I did it so I could play FSX or P3D since they are very processor dependent simulators! It just has a heatpipe heatsink, never felt like taking the time to insulate and use my autocascade on it which is why I only used a load tester. This used to be a great computer, it's in the death throes now.

Charles Wirth

08-10-2016, 05:41 PM

I also have a tandem compressor unit that hits -60c, it is charged with Iceon89

I am not doing IDF this year, but I should be back next year.

Elmor is doing the OC demo this year with Asus.

Did you want to get your cascade fixed? Needed parts?

aenigma

08-10-2016, 05:57 PM

I can fix it if I ever get the ambition to bring it in and work on it, mostly just a matter of straightening a bit of tubing, recharging it and hoping the digital thermometer that was laying on it didn't break. For the time being I'm just playing with the hobbled together autocascade I made. I'd love to see what these would do with ethylene instead of nitrous. Considering that it runs at about -94c to -96c with nitrous I know ethylene would get me below -100c easy. Too bad it's impossible to find, and will most likely cost an arm and a leg.

Just wondering, how hot does the second compressor in your tandem rig run? Mine is a small rotary that has been open to the air for the last 10+ years and I used to use as a vacuum pump, it's hot enough to burn me which is a bit worrying. Amazing it still works after all it has been through without even an oil change, so I'm sure it can handle it. This autocascade also sat outside with open lines for years getting rained on and baked by the sun before I even added the second compressor. I expected worse moisture and oil waxing issues, but only had a clogging problem with some cap tube where I spliced 2 pieces together and it's fine now.

Buckeye

08-10-2016, 08:03 PM

Charles Wirth

08-11-2016, 09:23 AM

Americold compressors, compressors in parallel, lineset and block swapped, removed solenoid valve, re gassed.

http://www.xtremesystems.org/forums/attachment.php?attachmentid=132192&d=1470935776

aenigma

08-11-2016, 10:22 AM

Oh , they're in parallel, I see. Mine are tandem/serial so the compressor piped after the first is like the surface of the sun while the first stays very cool. I didn't have enough pipe and fittings to pipe them in parallel, so just working with what I have.

Working in series does really increase the performance, but that second compressor suffers. If I had some small cap tube I could use liquid injection after the desuperheater to keep it cool. But it doesn't matter, it's hideous and just to play with haha. I got to -79c idle running just propane when I was testing it, that's how well series works. Lately it seems like everyday it gets worse, I think that compressor was already pretty much dead before I put it on.

That's a very nice system you have there, very clean and professional looking! I love that aluminum case for it. I've always been function over aesthetics, mostly because it's cheaper that way. :P

I just remembered I had some pictures of my first autocascade on my old myspace page. It's pretty rough looking too, I always planned on making a case for it if I decided to make it look good. Let's see if this link works, haven't used myspace in years. https://myspace.com/121149822/photos

Raziel

09-09-2016, 05:46 AM

I have being thinking a long time about making an auto-cascade and have being collecting materials which were thrown away at my workplace. The goal is to hit much lower than -100. I do not expect this project to start anytime soon. Since I have being working on a different project (car) for some time. sure like to read about previously built phase change, the whole auto-cascade thing sounds really tricky to me.

aenigma

09-14-2016, 08:32 PM

Yes it is very tricky, but very doable if you understand it. If you want much lower than -100c you are talking 3 stages or more, I am limited to only 2 stages and with a weak 2nd stage refrigerant at that. It forms an azeotropic blend increasing the boiling point of the nitrous oxide by quite a lot, but it is all I have to work with. If you want to discuss autocascade refrigeration you can contact me on skype, my screen name is Vibrophil.

Raziel

09-26-2016, 04:00 AM

I'm thinking about dividing the high stage(s) from the low stage(s).
This concept is usually done in big industrial refrigeration plants. Like in ammonia 2 stage systems with a booster compressor http://s21.postimg.org/exqadpknb/Cascade_idea.jpg , the principle used is a cascade condenser. I think this is beneficial because of the lower pressure difference between suction and discharge and the high and low side can have less refrigerants. Maybe that improves the efficiency of the compressor due to less "noncondensable" gasses. What do you guys think about that ?
Maybe this is cursing when speaking of an auto-cascade, it has was done before or it defeats the "simple" single compressor design. I haven't had the time to read everything posted. ;)

a bit incoherent -> will update this post. and make a drawing of the idea. did that.

aenigma

09-26-2016, 11:18 AM

So basically a cascade cooled autocascade? I've wondered about that myself, I imagine it would work very well by keeping a better compression ratio on the 2nd stage autocascade side. I don't have access to enough refrigerants to make it worth trying, but I have thought about cooling the r290/r744a autocascade with a high stage r290 system just to achieve a lower 2nd stage SST on the autocascade, I just haven't tried it.

Raziel

09-29-2016, 05:04 AM

Yeah cascaded auto-cascade :up: R290 is favorable for the high stage because of the low price.
I haven't crunched any numbers in excel yet. Still reading up on some research papers about auto-cascade cooling.

found this. https://ic.tweakimg.net/camo/c533d94fdd7cadbaa873aab1926498909ae68665/?url=http%3A%2F%2Fwww.icecoldcomputing.com%2Fgener ic%2Fimagehandler.php%3Fhval%3Dc84de0fdc0a38dc2963 0a847d2af34cf3fd5e039

aenigma

09-29-2016, 10:52 AM

I think you forgot to post your link haha. I haven't really read any research papers on autocascade since I never found much information about them back in about 2004 when I made my first one, so I just dived into it and figured it out.

The price of R290 is exactly why I use it, the same goes for my 2nd stage gas which is nitrous oxide. $70 for a big bottle beats $600 for ethylene even though nitrous isn't a very good refrigerant.

Raziel

09-29-2016, 11:42 PM

There is allot to be read.

Some links on scientific research
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.474.4455&rep=rep1&type=pdf
http://eprints.whiterose.ac.uk/95741/1/Experimental%20Investigation%20of%20the%20Performa nce%20of%20a%20Single-stage%20Auto-cascade%20Refrigerator_HMT.pdf
http://www.zju.edu.cn/jzus/oldversion/opentxt.php?doi=10.1631/jzus.A1000050

More info on stirling cooling
http://sunpowerinc.com/wp-content/uploads/2014/08/Doc0065-The-Free-Piston-Stirling-Cooling-System.pdf
http://www.stirlingultracold.com/lib/sitefiles/whitepaper/10354-GLOBAL-whitepaper-apr13-vF-web.pdf

some data
http://www.icecoldcomputing.com/library/reflib/Refrig_Data_Sum.pdf

I feel that somehow the auto-cascade hype has seen it's glory days. around 2008-9 most forums halt on this topic. Got the idea to make one 11 years ago. But I had to much other stuff going on back then to do this, and I now have the ability to buy directly from huge distributors.
Building a Auto-cascade is on my project bucket list. Though I still have my other project building a 400 hp turbo car, which still needs a substantial cash injection..

-->Added you to skype Aenigma<--

You mentioned ethylene would be better instead of nitrous oxide. Could there be a way to make this yourself? on the internet I find that this can be synthesised by dehydrating ethanol (ethyl alcohol) with sulfuric acid.
Both chemicals could be obtained easily. https://en.wikipedia.org/wiki/Ethylene

aenigma

09-30-2016, 10:57 AM

Yeah, seems like there is a lot of information out there on autocascades now, I just didn't find much when I made my first autocascade. Granted I didn't look very hard for it since I wanted to figure it out myself rather than just copying a schematic or something.

I am sure one could make it themselves but it would be a lot of time and money to get a significant amount. Even ripening bananas produce it which is why some places call it banana gas since it aids in ripening fruits, although it is not pure ethylene as they mix it with co2 or nitrogen I believe.

bthom

10-01-2016, 02:00 AM

I'm new to this subject but also very interested. Is an autocascade the same thing as a full two-stage cascade (two compressors with a refrigerant-refrigerant heat exchanger in the middle)?

Regarding ethylene I believe it's used for fruit ripening the other way around, meaning added to the fruit's atmosphere to make them ripen faster but it may also be produced by the fruit itself, not sure. I might even have some. Need to put a regulator on it to see if the cyl is full, empty, or somewhere in the middle.

In any case, I'm very interested in doing a two-stage cascade just for educational purposes. Trying to teach myself some thermodynamics and see how cold I can make an evaporator just using two old compressors.

aenigma

10-01-2016, 10:26 AM

An autocascade is one compresor with mixed refrigerants. It is like a casade, but it uses mixed refrigerants and separates them in a phase separator so your high temp refrigerant boils in the 1st stage of the interstage heat exchanger while the low temp refrigerant condenses in the 2nd stage of the interstage heat exchanger, to put it simply.

That is what I meant with the ethylene, it is used to riped fruits, but bananas naturally produce. For example you can put tomatoes in a bag with bananas to ripen the tomatoes faster. If you have a tank of ethylene and want to use it as a refrigerant you better make sure it is pure ethylene and not a mixture with co2 or nitrogen.

bthom

10-01-2016, 02:02 PM

Thanks, that makes sense on both accounts. The cyl I have is definitely just pure ethylene assuming the cyl isn't empty. Looks to be an 80cf half-height cyl with proper labels. No exact idea on age but definitely not recent. The last hydro test should be stamped on the cyl so that should put it within a few years or so. I'll take a look. I was google searching for some R23 or R508 in order to keep everything non-flammable. Ordering looks expensive though given it's just a self educational experiment, so ethylene may be a good option.

Does anyone know if there are any major concerns with using ethylene (or any other flammable refrigerant) other than the obvious that a circuit leak mixed with atmospheric oxygen plus a spark equals fire?

Regarding nitrous oxide, I thought about that as well. The temperature values look good but it's a strong oxidizer which most likely means what was clean on the inside of the circuit won't be clean for very long assuming regular copper tubing.

aenigma

10-02-2016, 11:35 AM

That would be perfect if you have ethylene, I would love to have some ethylene, you're lucky! It's about $600 to get a cylinder here. Ethylene is safe enough if you take the necessary precautions. The biggest concern would be a big leak possibly causing a fire and that would be very rare. Getting enough air in the system to actually make it ignite is more than unlikely. You would have to let the system be running in a vacuum with the low side open to get enough to possibly create a flammable mixture, and then be unlucky enough to have a winding short out and spark. I have been using propane as a refrigerant for over 10 years without any problems.

Nitrous oxide is inert, it is only an oxidizer if it is heated above 577c which is when it decomposes into about 70% nitrogen and 30% oxygen which is why it works well for drag racing. It has worked fine in my autocascades since i made my first one in 2004. It is only automotive grade nitrous though, so it's not that good. My biggest problem with the nitrous I have is that it boils at -88c but when it fractionates with the propane that boiling point is about 10 degrees warmer. It also has a melting point of -90c, so when I get to -100c I start running into the nitrous oxide freezing and blocking the cap tube until the temperature or pressure increases on the low side. I usually run around -80c to -90c anyway, so not a big deal. It does good for how cheap and easy it is to get.

aenigma

10-02-2016, 04:46 PM

Hey FUGGER for the last few weeks I have been unable to access my user account by clicking my name on the top right of the page or view anyone's user page, so I can't check my PM box or send messages. I thought it might be a bug that would be worked out eventually, but that doesn't seem to be the case. I would have messaged you, but I couldn't, so I figured I would ask you here since you posted in this thread. Thanks for any help.

Raziel

10-03-2016, 01:26 AM

bthom

10-06-2016, 01:35 AM

Thanks, that makes sense regarding n2o only being an oxidizer at high temps. Good to know it doesn't make a mess of the system at normal/cold temps.

Regarding ethylene, $600 seems expensive for what it is. Turns out the cyl I have isn't empty (80cf cyl currently showing 900psi), but now concerned about running out before I get something really working well. That would be depressing getting something almost working and then running out. The cyl here was given to me from long ago, but if it goes empty I would have to buy more. According to the Airgas catalog the part number for an 80cf of plant growth regulator (PGR grade) ethylene is "EY PGR80". Their definition of PGR grade is 98.5% pure and I'm guessing should be less expensive than CP or UHP grade. I'll try to get a quote before I get too far into it. Maybe what I have is enough though... I don't have a good sense of how much volume/weight is normally needed for a given size compressor.

Another point I'm concerned about is that the critical temperature for ethylene is well below room temp. So, while unplugged from wall power the system would equalize and go supercritical with no liquid (in the normal sense) being stored in a receiver/accumulator at vapor pressure. I'm sure there's ways to deal with it, as it would seem that also applies to systems that use co2 as a refrigerant, but I'll need to look into it further.

aenigma

10-06-2016, 12:22 PM

Nice, 98.5% should be fine to use as a refrigerant, my automotive nitrous is probably less pure than that since it is mixed with sulfur dioxide and probably has air and who knows what else in it. I would be very interested to know how much that PGR grade ethylene is. I was quoted a price for 'pure' ethylene. Nearly half the price was the shipping though. About $300 for shipping.

If you have 900psi you should have enough to work with, especially if you recover your refrigerant from the autocascade if you have to work on it to change cap tube lengths for example. The critical temperature for many low temp refrigerants is close to room temperature, that is normal. Nitrous oxide has a critical temperature and pressure of 36c at about 1060psi. That isn't an issue with a cascade or autocascade, especially if you have an expansion/buffer tank.

My first autocascade has a low side buffer tank and a hot gas bypass solenoid that will automatically open if head pressure rises above 300psi on startup. My latest autocascade I made out of junk laying around doesn't have a low side buffer tank and it is fine. It has a receiver which I turned into a phase separator and a suction accumulator as a secondary phase separator since I had it lying around and it adds a good bit of volume to the system. Static/base pressure is generally around 150psi, not too bad. Sometimes the compressor groans when starting, but it was made in 1989 and pretty weak. I added an old rotary compressor to make it a 2 stage to help it out. Just to clarify what I mean by 2 stage is that the original compressors discharge line enters the suction line of the rotary compressor, thereby reducing the compression ratio.

Raziel

10-07-2016, 04:17 AM

In the transcritical co2 systems the company I work at manufactures the compressor is started when the pressure in the receiver has risen. Although it is possible to make a system or a vessel that could support the room temperature pressure of the gas.
If you make a vessel that can withstand the pressure and you can pump down all the liquid and store it, then the system can be designed for a lower pressure. I have no experience in this. though I think it's possible.

@aenigma
Sulfur dioxide doesn't sound very nice. if it's acidic maybe you can purge it with a burn-out filter.
Or what I read on a forum is bubbling it through water seems to remove the sulfur dioxide, since it binds to water. Water is also not desirable but maybe better than the So2. if you can suck it through a filter drier into the system. Just an idea..

It is used as a refrigerant. hmm

bthom

10-07-2016, 06:06 AM

If you make a vessel that can withstand the pressure and you can pump down all the liquid and store it, then the system can be designed for a lower pressure. I have no experience in this. though I think it's possible.

I'm not completely understanding the idea but any more details would be greatly appreciated.

@aenigma
As far as I'm aware you shouldn't have to pay shipping if you're willing to wait long enough. I have no association with Airgas other than work purchases, but based on that the area rep should be able to get one sent at no cost to one of their regular stops assuming the rep can find a cyl with the right part number to shuffle around. At work we get direct shipments of the regular stuff (nitrogen, oxygen, argon, etc), but a normal stop would also be a local welding shop.

By "pure" I'm guessing they quoted CP grade (chemically pure).

That's very interesting you have a static offline pressure of 150psi. That would mean your system has enough refrigerant to operate but isn't completely 'saturated' (I'm sure there's a more correct term). If you were to keep pumping n2o into it, it should saturate at around 700psi and then some of it would turn to liquid at some place within the system. That wouldn't happen with ethylene at room temp. I can see the advantage of having a buffer tank so that a minor +/- in refrigerant charge doesn't make as much of a difference and makes the whole system less sensitive to a slight over/undercharge.

bthom

10-07-2016, 06:20 AM

I'm not completely understanding the idea but any more details would be greatly appreciated.

Thinking about it some more, are you referring to a self-regulating system where a surplus of extra refrigerant is stored in a high pressure container and an over-charge situation automatically pumps refrigerant from the system into the container, and an undercharge situation automatically releases some refrigerant into the system?

Raziel

10-07-2016, 06:54 AM

Thinking about it some more, are you referring to a self-regulating system where a surplus of extra refrigerant is stored in a high pressure container and an over-charge situation automatically pumps refrigerant from the system into the container, and an undercharge situation automatically releases some refrigerant into the system?

Yeah like that. Extract the surplus to keep the pressure low in the system. store it in the high pressure vessel and block it off with stop valves or solenoid valves.
Like when you pump down a normal refrigeration system by closing the receiver exit valve and bypass the low pressure safety switch.

aenigma

10-07-2016, 10:48 AM

I'm not completely understanding the idea but any more details would be greatly appreciated.

@aenigma
As far as I'm aware you shouldn't have to pay shipping if you're willing to wait long enough. I have no association with Airgas other than work purchases, but based on that the area rep should be able to get one sent at no cost to one of their regular stops assuming the rep can find a cyl with the right part number to shuffle around. At work we get direct shipments of the regular stuff (nitrogen, oxygen, argon, etc), but a normal stop would also be a local welding shop.

By "pure" I'm guessing they quoted CP grade (chemically pure).

That's very interesting you have a static offline pressure of 150psi. That would mean your system has enough refrigerant to operate but isn't completely 'saturated' (I'm sure there's a more correct term). If you were to keep pumping n2o into it, it should saturate at around 700psi and then some of it would turn to liquid at some place within the system. That wouldn't happen with ethylene at room temp. I can see the advantage of having a buffer tank so that a minor +/- in refrigerant charge doesn't make as much of a difference and makes the whole system less sensitive to a slight over/undercharge.

Yeah I believe it was 99.5% purity and chemical grade, it was a specialty gas so it would be drop shipped to me. I just got the quote by e-mailing them. Even without shipping it would be too much money to be worth it.

In an autocascade or cascade you need much less high pressure gas than you might think. If you start off by base charging the high pressure gas first when it is vacuumed you will only get about 25-50psi with a system that has quite a bit of volume. If static pressure was 700psi it would be wayyyyy overcharged. If I add any more my running high side pressure would just rise and increase the compression ratio eventually raising the evap temperature. A little goes a long way. The buffer tank is only used to keep static and startup pressures safe, it doesn't really make much of a difference when charging. Startup high side pressures before the high pressure starts condensing can easily get over 400psi without adequate storage volume which isn't good for the compressor.

My static pressure today was only 125psi since it is only 57f in the shop. Earlier in the heat of the summer when it was 90-100f in the shop it was around 200 I believe.

<edit> I forgot to mention it only has 100pm sulfur dioxide so it's not that big of a deal, it's the non-condensables such as air that it may have in it that I don't like. I don't know if it has much, but being automotive grade I wouldn't be surprised. Yup, sulfur dioxide used to be used as a refrigerant long ago, it's not a big deal at such low concentrations. They only add it so people don't huff it to get high. Also I think the reason my static pressure was only 125psi this morning is because my rotolock receiver valve must have started leaking again overnight as it was undercharged. Such is the way of the road when using old junk haha.

Raziel

10-09-2016, 11:17 PM

couldn't you buy a 2 stage lab freezer ie. Cold trap with r1150 in it and extract the gas? last saturday I went to a refrigeration scrapyard to look around for interesting stuff and the guy told me he had some lab freezers a while back with an ethylene filled second stage. too bad he didn't have more units.

Aenigma did you get a quote from linde gas ? I can purchase here. don't know about America. If you want, I could give it a shot.

aenigma

10-10-2016, 10:52 AM

bthom

10-13-2016, 05:35 PM

Yeah that would work, but I don't know of anywhere around here that would have anything like that. I live in a pretty small town. I didn't get a quote from linde but I am sure it would be expensive too. Ethylene is pricey stuff.

I checked at work just hypothetically if it were a work assignment (not just self educational), and it turned out to be affordable. All they had on file is a CP grade 300CF cyl but it was reasonable for even that, and I have to assume a PGR grade 80CF cyl should be even quite a bit less. I still need to call a local weld shop on my own to see what it would actually cost me personally as opposed to being a work assignment. They have a zip code dealer finder on their website.

bthom

10-13-2016, 06:18 PM

In an autocascade or cascade you need much less high pressure gas than you might think. If you start off by base charging the high pressure gas first when it is vacuumed you will only get about 25-50psi with a system that has quite a bit of volume.

Not sure if I'm following this. Not contesting, just not seeing the full picture I guess. Specifically not exactly following where the 25-50psi limit would come into play. I'm picturing a static system being charged to a static pressure then powered up to see if it all works as calculated. Seems the system should take as much refrigerant as you would like to insert into it until the inserted gas either liquefies somewhere in the system or makes the system pop a leak. Again not contesting, just trying to understand the bigger picture.

aenigma

10-13-2016, 09:45 PM

Not sure if I'm following this. Not contesting, just not seeing the full picture I guess. Specifically not exactly following where the 25-50psi limit would come into play. I'm picturing a static system being charged to a static pressure then powered up to see if it all works as calculated. Seems the system should take as much refrigerant as you would like to insert into it until the inserted gas either liquefies somewhere in the system or makes the system pop a leak. Again not contesting, just trying to understand the bigger picture.

Ah, sorry. It is not a limit, I was just saying for a system with an ideal amount of volume; such as receivers, accumulators and/or expansion tanks, it only takes 25-50psi of the n2o when added after a vacuum. It really depends on the total system volume of course. If you have enough volume it could be only 15psi and if you have no volume it may be almost 100psi. My point was you will never have hundreds of pounds of pressure from a 2nd stage static/base charge in a system.

You could charge the 1st stage refrigerant then add the 2nd stage refrigerant until it is working properly and shut it off, let it equalize and warm up then check static pressures and they still wouldn't be that much higher than the sst/sct of the high temperature refrigerant.

My skype is Vibrophil if you want me to explain this further.

bthom

10-14-2016, 03:01 AM

Thanks for the clarification, that makes sense.

My imaginary concern was that the system needs to drop down below the critical temp before the low temp refrigerant even becomes useful. At that point the system needs a certain amount of liquid/vapor refrigerant for the low temp section to function correctly. Once the system is unplugged from wall power that same amount of liquid has nowhere to go other than to turn back into very high pressure gas (which is different than n2o where it could max out at ~700 psi without popping the system and stay in the system partially as a liquid).

Sounds like I'm imagining way too large of a charge though and your clarification again makes sense. Thanks. Everything I've played with up to this point has had max pressures under 400psi or so, but again this is a learning experiment/challenge for me more than anything else. Just an experiment to see if I understand the math and see how far I can stretch it via the cascade/autocascade process without involving any other processes.

bthom

10-14-2016, 03:21 AM

One of the systems at work requires about 45lbs of liquid r22 refrigerant for a 5 ton compressor. Liebert calls it "lee-temp" in order to make sure the system still functions correctly during the cold winter months, still needing A/C indoors with ambient outdoor condenser temps well below zero C. There's no way that 45lbs of liquid r22 would stay anywhere within the system without popping it if the critical temperature and vapor pressure at outdoor summer temps and static offline pressures didn't line up with allowing it to remain mostly a liquid.

aenigma

10-15-2016, 04:20 PM

Wow 45lbs, that would be an expensive unit to fill haha. I am guessing it also uses a head pressure fan controller so the condenser fans only operate when needed.

These autocascade are much smaller, we are only talking about ounces of refrigerant and an autocascade always takes more 1st stage gas than the lower stage gasses. When the system is off then the low temp refrigerants will turn back into vapor and just increase the base static pressure of the liquid 1st stage refrigerant. This is why you want the expansion tank depending on how much low stage refrigerant(s) you add. Especially when it is more than 2 stages.

On my autocascade if I close the 2nd stage discharge line valve the head pressure can get up over 300psi since it isn't condensing the nitrous, just compressing it and storing it in the receiver without entering the interstage heat exchanger. When I have it running normally, like I do right now, high side pressure is only 195psi and my evap is -102c, but it is very cool in the shop at about 14c.