Morphing Air Conditioner into Autocascade System

Ah, do you know the foam density? Great Stuff isn't very good, so I'm purchasing some two part pour 8lb density foam.
Ah one last question again, do you think r11, r290, r23, r1150 might be a plausible creation? One more HX added then your design. Most likely 9' capillary lines. So r11/r290 condensing r23, r23 condensing r1150. I know its not straight like that, as the first r1150 to condense will most likely be liquid or saturation in r23, and thus help more r1150 condense. But in our systems colder is better, and ethylene is readily available and used in cascade systems of ours.

Here is another picture of my Cold Trap machine giving you a more "bird's eye" view of the compressor, air-cooled condenser, fan, and the modifications I made (bullet style liquid line dryer, suction and discharge access fittings). This also shows the corrected position of the suction access fitting, which fixed a small boo boo I made on the initial build (I accidentally had it pointing towards the front which you can see is occupied by the electrical box).

As part of the modifications, it is also necessary to cut the rear motor shaft and remove both the evaporator fan and evap (these were originally inside the Styrofoam box). Actually the evap is another bonus which could be used as an air-cooled condenser for some other project.

I've worked with an almost the same AC before, making it into a chiller with the evap coil actually in a cooler. Works pretty damn well. Very nice work again Mytek. If you take a dremel to the shaft that would be on the recirculator, it spins the shaft as you cut, works great ;)

Quote:

---

Ah, do you know the foam density? Great Stuff isn't very good, so I'm purchasing some two part pour 8lb density foam.

---

We use a MIL-SPEC foam which I don't recall the density of (I can try to find out). Yes Great Stuff is not a good substitute (whatever happened to the real polyurethane in a can?).

Quote:

---

do you think r11, r290, r23, r1150 might be a plausible creation?

---

Yes, very plausible. R290 instead of R22 I presume. The R1150 should do nicely to get you to -100C although R14 would be even better (understandably more expensive and harder to get in small quantities).

R23 and ethylene are hard to get as it is in small quantities, R14's incredibly pricey to begin with, though with a subcooler r14 and argon work nicely I've seen. But yes, r290 instead of r22, though I might use r22 as well. R11's good with oil but so is r290, in a way a bit more security to remove oil.

Mytek, in looking for compressors in this or any application, do you deem HP to be more important, or displacement, or what other variables? Do you prefer rotary due to greater vacuum vs reciprocating having a greater displacement?

Just a thought...
I am not sure what kind of oil comes in these units, and for the temperature I was designing for it was not an issue, but when going colder it might be.

I would hope that it would be charged with POE, but being made in Korea I have my doubts. Does anyone know? The compressor is an LG QA075CDE in a Goldstar GWHD5000.

If it can't be verified, then I would suggest changing out the oil for systems intended to being used down below -40C. Zerol 150 would be a good choice, although a POE type would also be good.

AB my guess, since its a rotary, and its designed with r22 originally. I dont think oil's a problem with each phase sep also acting like an oil sep.

Quote:

---

Mytek, in looking for compressors in this or any application, do you deem HP to be more important, or displacement, or what other variables?

---

Tricky question. Displacement would be key. But depending on the system running pressures, having too small a motor for a given displacement could lead to a burned out motor in short order.

Quote:

---

Do you prefer rotary due to greater vacuum vs reciprocating having a greater displacement?

---

I kinda like the rotaries myself. Nice to have so much punch in such a small space. Although reciprocating compressors do have a lot of volume on the suction side housing, sometimes making the need for an external expansion tank unnecessary.

Thanks again for letting me pick your brain like this; oddly your PM feature doesn't seem to work for your user name. I find most rotarys to be louder then something like a danfoss nf11fx. Which is 3.5cc larger displacement then that rotary, and actually probably a higher hp. So I wonder if it would serve better then that rotary...

Quote:

---

I dont think oil's a problem with each phase sep also acting like an oil sep

---

Don't count on it! On the Polycold units I work on, even with an oil having a Floc point of -100F we still see oil freeze ups occur (and we use very large phase separators). Of course we are operating down to -150C or colder, and not using either R-11 or R290, which are both excellent solvents for oil.

It would seem wise to not take the chance, and change out the oil for something with a low Floc point. This would be fairly easy to do early in the build, by cutting the suction line above the accumulator, draining and measuring the original oil, and then adding back in the same amount of new oil (having a little bit of the old oil left won't hurt).

Hmmm, is mineral oil not any good for really cold temps? Dang, that means I might have to change my oil...and POE is such a PITA.

Of course, I'll probably not be dealing with super extreme temps, and will likely be using r-290, so I may just not worry about it ;).

Yes, changing oil on the rotarys is a two step process. Gotta drain the top and the bottom. What about an actual oil separator after the compressor, oil output cooled via a small heat exchanger, and still having two very miscible refrigerants in the loop like r11 and r290. I think oil problems would be heavily minimized. Though with -150C I'm sure they'll always occur.
I just really thought about it though, that rotarys .33hp, and 7.5cc. The NF11FX is .375hp, and 11cc. Its also pretty quiet and compact. I wonder if in an autoc operation like this if it would perform better with higher loads, since probably would still have a higher suction pressure.

:Added: Also, in our somewhat small application, if the static pressures too high expansion tanks are often easy to make, either with heavy copper tubing (bit pricier) or the odd way of draining a propane torch bottle for a 1L setup, or picking up cheap small copper spun accumulators and daisy chaining...

:Added again: Though with rotary that accumulator is one hell of a benefit.

N00b I missed this one early, and just caught it when I was reviewing this thread.

Quote:

---

R14's incredibly pricey to begin with, though with a subcooler r14 and argon work nicely I've seen

---

Yes especially with a subcooler following the 3rd cascade, you can indeed get some pretty low temps using Argon with the R14. However for the typical loads desired from a PC Cooler (200 watts+), the desire to keep the overall size of the unit small, and the power supply requirements within reason, Argon should only be used sparingly.

Under the conditions I stated above, having more then a couple % of the refrigerant gas pressure made up of Argon, will very quickly send your compressor discharge through the ceiling.

If you can live with an operational range of -100 to -110C, then no Argon would be the better way to go.

For people that don't understand how using Argon (which wont condense in a typical autocascade) can create a colder running system, I would point you back to my earlier post in this thread that discusses the principle of gases dissolving into "subcooled" refrigerants, and thereby creating a pseudo refrigerant with boiling point temperatures lower then the condensate that formed the base.

Edit: Also the presence of Argon gas in the final evaporation stage helps to create what appears to be a lower pressure environment, due to the principle of partial pressure (reference: Low Temperature and Cryogenic Refrigeration).

Yep, I'm sure with these size units argon would be a no-go. I picked up a 5150btu Kenmore yesterday and am beginning basic rip down. You definitly have given me some great ideas, mostly since to me $89-95 is worth it for the condenser and fan assembly, especially with a nice small rotary there as well.
Well, time to pickup a roll of 3/16" and see how small I can go later, and get another price on r23 and r1150.

If I do get r23, I will try and compare r11, r290, r23 with similar sized condensers, exact sized hx and capillarys, and only swap the rotary for a nf11fx.

:Added: And finally, will eliminating the r290 (or in your case) r22, lengthen the pull down time considerably?

Quote:

---

N00b asked... will eliminating the r290 (or in your case) r22, lengthen the pull down time considerably?

---

First of all it depends on how many stages we are talking about using in the autocascade. ASHRAE describes a system as I used for the Cold Trap project to be a single stage autocascade (reference). So if we are talking about single-stage systems, then I would say that R290 or R22 would not be required or needed to obtain good results. This would be especially true for binary mixtures. However a single-stage can only be taken so far before you would run into inefficiency problems, or should I say limitations. Most likely you would need to go to at least a two-stage autocascade using 3 or more refrigerants when trying to make or break the -100C mark.

If your goal is -100C, and you choose to leave out the R290 (R22) and only use something like R11 or R123 as your high boiler (and assuming you are trying to do this with a two or three stage autocascade), you will experience a "disconnection" centered around the middle of your autocascade. If you were to thermocouple the In's and Out's of all the heat exchangers as I earlier suggested for new designs, this effect would be very noticeable showing up as a colder then expected 1st stage, and not much work being done in the following stages. If you were to add R290 (R22) while operating the system, you would suddenly see the colder temperatures shift downstream, and the "disconnection" disappear.

Back in the CFC days, the preferred choice for the high boiling component was R114, having a boiling point of about 3 degrees C. A charge made up from R114, R13, and R14 would produce excellent results in the -100C arena. Since R114 was banned some time ago (as well as R11), you will probably have to use a combination of two refrigerants (R123-R22 or R123-R410A or R123-R290 , ect.) to try to mimic the same boiling point. Of course since you seem to have access to R11, you could substitute it for the R123 (I hope you employ proper charge recovery).

By the way... Thanks for all the great questions, and the obvious enthusiasm :D

Edit: R236fa would be a good HFC replacement for R114, possessing a similar boiling point. It also goes by the name of FE-36 when used by the fire extinguisher industry as a replacement for Halon, and can be purchased in small quantities from places like Complete Off Road.

I will use all proper recovery when working with something like r11. I try to always recover when I have to.
Since your talking around the 9c range, what about butane or isobutane? I'm also assuming the disconnection is bad ;) or am I assuming that incorrectly.

Not using a "middle-stage" gas like r-290 doesn't sound very pleasant and/or useful if I'm reading that correctly, which makes sense. Cascading the gases in gradual steps strikes me as the way to do things, the drastic jump, if even possible, of ~0*C to -80*C or greater sounds hard if not impossible.

MytekControls, would you know of a good book that covers autocascade theory? You said you do the calculations from intuition which makes sense since you have been doing it so long however you had to start somewhere :D I'll just keep plugging away with my test setup, every day I learn something else.

Its not a 0C to -80C jump. Gaseous r23 would saturate the liquid r123, and cause the bp of the r123 to drop so drastically that condensing more r23 would be easy.

I see, same principle as done with argon and r14? I see R123 boils @ 27*C @ 14.7psi and r23 boils at -82.1*C @ 14.7 psi, once the initial startup is done then the 1st stage will have a hybrid gas that boils somewhere between 27 and -82 celsius depending on the amount of r23 saturated in the r123? Is there a listing of various gas combinations that will saturate into 1st stage gasses, there's got to be some chemical property that lets them mix so easily.

Well I think it comes down to polarity. R14 is incredibly polar, but that doesnt make much sense with argon now does it... But hydrocarbons are non-polar and so love each other dearly ;)
Ultimately I think most gases will do it since they're under pressure.

I think you got some things confused n00b. r14 isn't polar. second of all polar molecules tend to bind better with each other then non polar molecules. think of water.

you probably mean electronaffinity of the atoms within the molecule.

I don't know if your assumption here comes directly from a post I made a while back about mixing refrigerants with electronaffinity in mind but if you did read it again.

Very cool, I have a few of these in the garage that I haven't had a chance to mess with yet. This just gave me the jump start to go be creative!! Awesome info too, will be very helpful to most.

A noob shouldn't start with a autocascade. It is very complex, even when it don't look so!

Quote:

---

MytekControls, would you know of a good book that covers autocascade theory? You said you do the calculations from intuition which makes sense since you have been doing it so long however you had to start somewhere

---

The only books I learned from were in my earliest years, and was from some very old school text books on physics that covered various conventional refrigeration systems. This gave me a good foundation which I built upon when I first started working for Polycold in 1977 (I was 21 years old at the time). Most of what I learned about autocascades came directly from working with their systems. The education was almost purely derived through hands-on, not book, related learning.

My mentors consisted of the 3 original partners in Polycold, including the main creator Dale Missimer. Dale was heavily book learned, college degreed, and not much of a hands-on type of guy. The other 2 partners were definately of the hands-on variety, and it was through them that I initially learned the basics. In the later years Dale had taken me under his wing, and it was through this experience that I really started getting involved with the design process.

I never went to college myself, and have never had a strong math background, so my approach has always been more intuitive, based in large part on empirical test results (of which there were many). I have found that the human mind's greatest asset seems to be in it's ability to sort through and recognize patterns in literally thousands of tiny details. It is most likely the best multi-tasking, multi-threaded computer that will ever exist. And it is because of this, that I believe intuition is much more then just a lucky guess.

Basically the more tests you conduct, and the more data you look at, the better will be your ability in creating working autocascade systems. This is why I also stress the importance of thermocoupling the In's and Out's of all the heat exchangers in your new designs. Viewing the temperature profiles under various conditions of load, refrigerant mixtures, and cap tube/heat exchanger sizing will begin to create this intuitive link within your own mind.

You will be hard pressed to find a single book that will do this (especially on the subject of autocascades). However for the person just starting out in refrigeration, a good initial background in conventional techniques and safety as related to compression based refrigeration systems is a must. This can be learned from books and/or from a good mentor.

Here is some good background info on Polycold and autocascades Some of this you may have seen before when cryotec posted a short history on Polycold a while back.