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Hi, I was wondering what would happen if someone were to put to compressors in serial in a single stage unit? As in the discharge port from the first connects to the suction port of the second one. Anyone understand or should I draw a diagram?
Thanks
That'd be series, but I'd imagine you'd burn the compressor in front out with the hot discharge from the one doing most of the compressing, and you'd manage a lower low side pressure.
Woops, your right it is serial, i'll go edit my post. So pretty much it wouldn't work.Quote:
Originally Posted by n00b 0f l337
I'd think you'd have to desuperheat/cool the discharge. And then you'd risk sending liquid refrigerant at your other compressor.
But two stage compression does exist, so it has to work in some way, unless the systems are rated for dealing with that sort of work load.
If you want to play with two, try two in parallel. ;)
I see :up:Quote:
Originally Posted by n00b 0f l337
Sorry for a silly question, but how would I put them in parallel, instead of serial?
EDIT:
Like this?
http://i292.photobucket.com/albums/m...y1992/SS-1.jpg
danfoss make comps like this :) in condecing units
http://www.extremecooling.net/random.../danfoss/2.jpg
Thats a whole lot of cooling power you got there Carl.
Hey fatguy, that parallel Diagram looks pretty much right. You might wanna put a DSH after each comp though. Or have an enormous condensor
How do you ensure proper oil return though?
:) there not mine it was just for illustration could not find the pic on danfoss's web so used this pic from cold_ice's threadQuote:
Originally Posted by Postal Dude
there will be no need to on such a small systemQuote:
Originally Posted by sjg0
Looks like you could have a nice lil project there fatguy. Good luck with it. You using recip or rotary compressors?
What gas you looking to use with it?
First i'll build a normal SS with my 1 & 3/8hp compressor, then i'll try making the dual compressor unit, with another compressor from a small AC unit off ebay. Not sure on what gas to use, would have to use anything special, or just R507? Also whats a DSH?
Then if it goes all good, I might try a cascade one day.
Anyway I can't do much till I finish school this year, then i'll have heaps of time and money :D
Thanks
Still dont get the point...if your going to use 2 compressors just build a cascade and maximize your temps.
its good if you got 2 matching small comps like 6-8 cc then you can do more with them but if you got a comp bigger than 11cc like you say theres not much point:)Quote:
Originally Posted by sdumper
The only I reason I would is just for practice and for fun :)Quote:
Originally Posted by sdumper
Thats cool..Id enjoy following your log on that because things have gotten pretty slow around here lately and I am too broke to start any new projects so have to live vicariously :(Quote:
Originally Posted by fatguy1992
ThanksQuote:
Originally Posted by sdumper
Unfortunately I won't start any builds until October, no time or money till then :(
You could connect the service ports, if one has a little bit higher oil level for whatever reason it'll flow through the tube there, unless for whatever reason there is a pressure difference between the compressors suction sides...Quote:
Originally Posted by sjg0
If you put compressors in paralel is there any change of final temps?
If not then like sdumper said a cascade would be a better choise.
It would increase capacity, allow you to have a real high load, maybe good for a 1st stage of a cascade, but you can't really push the load limits of a single compressor in a single stage, the max heat output of a CPU is what, around 200 watts or so?Quote:
Originally Posted by The Shooter
Thats @ low GHz and volts. i7's easy produce 350watts+.Quote:
Originally Posted by [486]
:shocked: That is almost 30 amps, now I see why they use an 8 pin connector! I actually think that is more wattage than my entire computer uses!Quote:
Originally Posted by fatguy1992
I really have been out of the computer "loop" for a while...
Hmm... I hadn't thought of that.Quote:
Originally Posted by [486]
It still doesn't help though, because I think this thread is referring to the small, 7cc Rechies listed on ebay. Rotaries don't have service ports :(
With reciprocating compressors you simply drill a hole in the bottom of the case and link the two compressors with 1/4" tubing. The oil levels will equalize during operation. With rotary compressors I guess you can do the same thing.
But what happens if you have a slight difference in the suction lines or something that would cause higher pressure in the other, like a bit of brazing material at one side of the T fitting connecting the 2? If the tube was at the bottom then a lot more oil could transfer than using the service ports.Quote:
Originally Posted by [XC] gomeler
I'd assume the whole thing wouldn't matter much as the oil in the systems moves through the tubes and all, if one compressor had a little more oil it would just pull more into it's intake and put it through the system, no harm done. Besides, the valves on the recip. compressors are reed valves, so they can handle a little oil, just a cylinder full of it will wreck the con rod... I think this might be the principle that the condensing units that have 2 compressors in parallel work on...
Here is a picture of a 2-stage ammonia plant at the Technical College of Jutland (Denmark).Quote:
Originally Posted by n00b 0f l337
http://img20.imageshack.us/img20/5026/2stageammonia.jpg
Hi I have some questions. Has some one already build these "dual" single stages(any work logs)? Is it worth it? What would you say about a dual Danfoss FR7.5G, R507 setup?
I think someone used two compressors in parallel in the 1st stage in a cascade. I haven't seen it done in an SS though.
http://www.xtremesystems.org/forums/...ghlight=tandem
It can be used only one bigger condenser.
If you put a heat-exchanger between the two compressors, heat won't be an issue. But then I would have two HX. One after the second, and the other between them. If you really want to get overly dramatic, depending on which refrigerant you're using, you could put one before the first compressor as well.Quote:
Originally Posted by n00b 0f l337
Then I would suggest connecting the heat-exchangers in series from the processor back to the condenser. That way you're progressively cooling them in order from the coldest to the warmest refrigerant in line.
I'll have to read the rest of this now to see what anyone has said about oil management. Because with two compressors, you need to distribute the oil evenly between the two.
EDIT: You should see the new Sanyo two-stage compressors in one unit! Search google for them. I believe there are other companies now making them as well.
Shingoshi
In that case, they used a reservoir for all of the compressors and used an oil leveler to make sure each unit was properly fed.Quote:
Originally Posted by [XC] gomeler
My only question is, how safe is it to do this? Do you need a diagram to know where to drill the oil lines? Otherwise, doing this blind could be problematic.
Shingoshi
Then you have liquid refrigerant going into the second compressor.Quote:
Originally Posted by Shingoshi
Two stage compression isn't that hard of a project, but you need a phase separator in order to prevent low stage compressor to suck in liquid refrigerant. Also the refrigerant of choice must be able to operate at high and low pressure. It's possible to achieve very low temperatures but cascade is a better solution though since you can choose refrigerant for each cycle separately.
So - if you have two appropriate compressors:
- for very low temperatures go with cascade
- for very high cooling capacity go for a tandem.
I meant a reservoir for the OIL. They used a COMMON OIL RESERVOIR connected to the oil sumps of each compressor. They then fed all compressors their oil from that reservoir, using an oil leveler.Quote:
Originally Posted by [486]
I think I missed your point! Yes, if there were no separator used, you would get liquid instead of vapor going into the second compressor. I just didn't think that was necessary to be explicit, since I thought that should already be known. Sorry for the assumption.
Hope that clears up any confusion.
Shingoshi
An oil leveler? When performing multi-stage compression the compressors will have different suction and discharge pressures. You can't simply pipe the oil dumps together as the pressure will equalize and shortcircuit your loop. 2 stage compression is best accomplished with a single multistage compressor.
Tandem compression is simple as the pressures are identical.
A note, it may be possible to operate a multistage compression system with the sumps connected via a solenoid. Run the system for a few hours and then powerdown and equalize the oil. Not worth the trouble though, a cascade will dare I say be safer.
Again! Why??:shrug: Because you can? use some logic:)
Quote:
Originally Posted by sdumper
Nuff Said!Quote:
Originally Posted by [XC] gomeler
I know I'm old and i don't like change, haven't been around for awhile (maybe for the best:clap:) but where has Phase forum gone:shakes:??
As I was searching Google for methods of using parallel compressors, this is one of the links I came across.
Parallel compressors single condenser
This is the link where the discussion of oil came into play:
A very effective oil return system is key to success
I hope this explains what I said and why.
Shingoshi
+1Quote:
Originally Posted by gosmeyer
Its been very slow lately...
I might start posting some SS bencher builds just to break the routine...
You do that, Scott. Hell, i've been posting chiller, auto-cascades, cascades, waterblock to evaporator modifications. It seems as I'm the only one left working on something in here.
It's rather sad and lonely :shrug:
Quote:
Originally Posted by tiborrr
I was just thinking that you were really the only one building anything cool lately.
Nice work on that autocascade!!
Hopefully this Fall and winter I will contribute a build. For now I must be content to play with chew toys :D
LOL have your fun ultralo1. As for myself I'm financially broke beyond belief until my student loans come in. When that happens though I'll have a little fun.
Gom, stop tearing away the mobo sockets, it might help the budget :P (this is being told by a person who ruined two M4A78T-E in a three weeks)
:lol:
http://cgi.ebay.com/COPELAND-SCROLL-...d=p3286.c0.m14
Tandem Scroll Compressors. This is how you build a tandem compressor system. Notice the oil equalization piping at the bottom with the sightglass. Imagine building a gigantic autocascade with this setup :D
And I'm wondering how well this layout would work for me? My compressors are 230v R-22 2-ton units.Quote:
Originally Posted by [XC] gomeler
Shingoshi
Quote:
Originally Posted by Shingoshi
Hey guys,just a reminder, don't forget R-22 starts it's phase out per "Montreal Protocal" Dec 31. remember how R-12 prices went ballistic.......... I don't have a crystal ball but quit a few extra pallets warehoused.:yepp:
I've got 2 jugs in storage back home to resell later :DQuote:
Originally Posted by wdrzal
Maybe you should have known about this!Quote:
Originally Posted by wdrzal
ISCEON® MO99™ refrigerant
Google can be so kind if you ask it to!
Shingoshi
I'm not quite certain what Walt's angle was on that but I would be willing to bet he's looking to resell it, hence why he'd store a few pallets. Like any commodity, prices will spike once production has ceased and the man sitting on a pile of said commodity will have a nice pay day as demand won't stop for a while.Quote:
Originally Posted by Shingoshi
to eliminate the oil level issue on hermetic compressors in paralell; you simply drill a hole in the bottom of the shell, and drill a hole at the upper part of the compressor, or use the service pipes to equalise the gass pressure. By doing so the oil flows freely from one compressor to the other. If one compressor is not running, ther wil be no problem since the compressor high pressure valves are shut due to the pressure difference.
I just got confirmation of my compressors being shipped now. Can't wait to see these things. Having two York 2-ton compressors in parallel should be a blast!Quote:
Originally Posted by mEsUsah1
Shingoshi
off topic please post in your own thread.Quote:
Originally Posted by Shingoshi
So was this also off-topic? It was a point raised here, not in my thread. And I believe it was already commented on. I simply stated that this wasn't a concept only to be left up to the imagination. What's the point in people providing ideas, if no one is expected to use them? I gave no further details here about it. Instead, I did that in my own thread. Sorry I ruffled you.Quote:
Originally Posted by [XC] gomeler
Shingoshi
Thanks [XC] gomeler: I thought I read the title here as "2 Compressors In A Single Stage?"
Easy guys, no need to get up in arms. Shingoshi was just informing us that he purchased two compressor for a tandem compression experiment which is relevant to the last month's discussion in this thread.
Would it be possible to use one compressor before the condenser and one after it? I'm thinking that if you use a refrigerant that wouldn't condense but lose most of it's heat at room temperature (from the first compressor), you should still have vapor entering the second compressor. The second compressor then would need effective subcooling to get the refrigerant to condense to a liquid. Or does this then qualify as a two-stage system?Quote:
Originally Posted by n00b 0f l337
Shingoshi
The system you are talking about is a two-stage system. You should know what you are doing if you atempt this. If the "condenser" (really a gas cooler) is to efficiant you wil have liquid out of it. But the good thing about this if you do it right is that you will have a lower spesific volume, and lower gastemperature. That means lower displacement on the sencond stage, and lower power consumption overall. It's a good idea to have a liquid seperator after the gass cooler (middle pressure cooler) to avoid a broken compressor. :) In industrial cooling this is actually a normal way to do things ;) (mainly because you will have lower gas temp into the condenser, pluss a lower power consumption)Quote:
Originally Posted by Shingoshi
As always, click on my images to see the links they point to!
I'm guessing you'd want to use something like this:Quote:
Originally Posted by mEsUsah1
http://www.rparts.com/Catalog/Major_...ccumulator.jpg
So then the question now becomes,
1.) Which refrigerants are pretty much guaranteed not to condense at room temperature? R-744?
2.) Specifically, which refrigerants need very low temperatures to condense? I know that R-14 is a candidate.
3.) Should both compressors be a different size? The first one larger than the second?
4.) Could such a system function with only a single refrigerant? Or would you still need another seeding refrigerant (like R-600a) to work for the subcooler downstream from the second compressor?
5.) Could you have a combination of refrigerants all incapable of condensing at room temperature? (That seems to make sense)
6.) So which refrigerants require an even lower condensing temperature than R-744/CO2?
Shingoshi
EDIT: Sorry for repeating myself. I keep re-editing my text, and I wind up with redundant questions.
EDIT: I always learn so much from these guys!
http://www.refrigeration-engineer.co.../header_07.png
EDIT: I think this applies to this subject as well:
http://www.wipo.int/pctdb/images/PCT...gz_en.x4-b.jpg
I got my new compressors today. I've posted pictures of them in my thread.
The Towers of York
[IMG=http://img27.imageshack.us/img27/5177/compressortwins.th.jpg]
Shingoshi
1,2)This is kind of andvanced stuff but anyway. You don't look for a refridgerant that does not condense in room temperature. You can do this with every rifridgerant. You just "get rid of" the gas superheating (cooling the gas, so it gets closer to condensing temperature at the spesific pressure).Quote:
So then the question now becomes,
1.) Which refrigerants are pretty much guaranteed not to condense at room temperature? R-744?
2.) Specifically, which refrigerants need very low temperatures to condense? I know that R-14 is a candidate.
3.) Should both compressors be a different size? The first one larger than the second?
4.) Could such a system function with only a single refrigerant? Or would you still need another seeding refrigerant (like R-600a) to work for the subcooler downstream from the second compressor?
5.) Could you have a combination of refrigerants all incapable of condensing at room temperature? (That seems to make sense)
6.) So which refrigerants require an even lower condensing temperature than R-744/CO2?
3) Usually the first compressor (that sucks superheated gas from the evaporator) is close to 3 times larger than the sencond compressor. This is due to the lower spesific volume on the gass after the intercooler.
4) The difference between cascade and traditional two-stage system is that you just have one refridgerant in a two stage system. (The same refridgerant runs through the entire system). In a cascade you can have the same refridgerant, but they run in a independent loop that heat exchange (The 1st. stage is condensing against the 2. stage evaporator).
5) You chose refridgerant based on the pressure and temperature you want the system to have. Things like oil blend capability, and oil types is also a factor. The critical pressure/temp (the maximum pressure that a refridgerant can have in order to condens/evaporate) is a major factor.
6) Nitrogen has an extremely low critical point. (34bar/-147c) But this is not what you want to consentrate on.
Hope this helps! :)
1+2.) Let's concentrate on R-744 as my baseline for this discussion. I need to look at how much pressure I need to get the condensation point low enough to work with. I need to take the time to convert bar to psi to see what I'm working with here. My main concern is that I don't want too much pressure inside my gas coolers. Specifically because they weren't designed for this (They're actually very large 32"x12"x3" Turbocharger Intercoolers). So I don't want the pressure inside of them to be higher than say 200psi. I want to use my smaller compressors to bump the pressure up from there.Quote:
Originally Posted by mEsUsah1
3.) My two compressor sizes are 19.6cc and 7.75cc respectively for the Matsushi+a (York) and Rechi. That's about a 2.5x difference between them.
4.) I have a total of six compressors. Two York and four Rechi. See my link I posted above to see them together. I want to use the two York (Panasonic/Matsu) compressors in tandem/parallel for my first stage. I simply want to them to provide for the system's volume/load capacity. I then want to divide the four Rechi compressors into two separate tandem/parallel groups. The first tandem group will be used to bump the pressure of the refrigerant up coming from the gas coolers. The second tandem group will be used to subcool the refrigerant leaving the first group, passing the heat back to the outbound refrigerant.
So there will be two completely separate refrigerant loops in the system. The first loop will have the combination of both the York and Rechi compressors. This loop will likely have R-744 as the main refrigerant. The Yorks will be (first-stage) before the gas cooler, and the Rechis will be (second-stage) after the gas cooler. The second independent loop will have only the last two Rechi compressors to provide the subcooling. The subcooling loop will likely have R-600a as the refrigerant. The two loops (main flow and subcooling) will run in counterflow. The inside subcooling Rechi loop is moving refrigerant in the opposite direction against the main incoming refrigerant loop. Instead of the subcooling loop having it's own condenser, it will use a heat-exchanger to cool the subcooling refrigerant with the refrigerant coming from the evaporator of the main loop. This will also be done with the two Rechi compressors in the second stage.
I'll leave 4+5 alone for now.
Thanks for your time!
Shingoshi
I imagine you have made some autocaskade/cascade systems. When you build two-stage systems you have to think a bit different. And R744 (CO2) is really different from the usual refridgerants. I'm sorry but i'm not used to working with psi (i live in europe). R744 has a critical point of 73,6bar (31.1 °C). In other words to make a traditional system with condensing, and subcooling you must have a pressure below 57bar(20°C).
This is how a typical transkritical 2-stage R744 the system is buildt. As you can see the pressure in the middle pressure reciever is quite lower than the gas cooler pressure.
http://i939.photobucket.com/albums/a...ah/CO22STC.jpg
http://i939.photobucket.com/albums/a...ksbeholder.jpg
This system solution does not requier external cooling. and will give a good cooling capasity with low mass-flow. And therefor a low compressore displacement. Sub cooling before the evaporator vent is not neseserry in so small builds. You recomand having a suctiongass-heat exchanger on the low pressure compressor. Leting the middle pressure liquid heat exchange with the suction gass from the evaporator. This will superheat the gass before the compressor and subcool the liquid before the evaporator. And then secure your low pressure compressor from "liquid-hammering" (destry the compressor).
EDIT: Usually you have a 2 times larger dispacement on the low pressure compressor i R744 systems.
The valve between the gas cooler and the middle pressure reciever is important if you plan on running transcritical. If you don't have it you'll have a low evaporator performance.
I do not recomend building a sub-critcal system with R744 if you dont heat exchange the condensation with another refridgeration loop (cascade)
A solution for subcritical R744 is something like this:
http://i939.photobucket.com/albums/a...sah/CO1SCC.jpg
This is a good way of doing things but requier a lot of automation + oil return systems.
Hope this helps.