Cascade Question

[fatguy1992]

Hi i'm planing out a cascade to cool 2x high end GPUs and I was wondering which of these two designs would work the best. I know that it would have hold a lot of heat.

1. 3 stage cascade, r404/1150/1150 with dual heads.

2. 2hp compressor as first stage cooling 2 separate 2nd stage loops each with its own compressor 1.5hp.

Second option I could run either 1 or 2 heads depending on the benching one or 2 gpus.

1st stage condenser...

http://img28.imageshack.us/img28/8292/bild0941.jpg

Thanks

[Patrickclouds]

how much load do you need on your evaps? 300watts each?
which displacements have your compressors?

are you using ethene on the second stages? no cold problem with the gpus?
i would choose 20-24ccm in your second stages r1150 and 48ccm in the first stage r404a or r507

[fatguy1992]

I was thinking about 300-350watts for each GPU. The 2nd stages would have R1150 in them and if the GPUs have a cold bug then I won't bench them

[Patrickclouds]

then go with the 24ccm rotarys on the second stages.
on first stage i´m not really shure what size you should choose.

toaster has build a strong cascade with only one compressor and one evaporator on second stage.
400watts on second stage evap. first stage was a 36ccm rotary.
so if you double the size of the first stage you end up at 70ccm which could be a maneurop mtz40 (68ccm, 11,8m³/h)
you can calculate your unit with coolpack and refrigeration utilities. i end at 9-10m³/h on first stage

[sdumper]

Sounds like a fun project...

[fatguy1992]

Alright thanks, so you think the 2nd design would be the best one?

Fatguy are you in the US? Im wondering because if you go as big as your describing then 115v compressor wont be available in the sizes your after.

No i'm in Australia, I already have the 2hp compressor in a 2x headed GPU SS.

[fatguy1992]

BTW has anyone built a 2x headed cascade before? If so is there a link to their build log? I couldn't find any.

[Patrickclouds]

here we go but with one compressor in the second stage:
http://www.extremecooling.de/forum/t...Rotary-Kaskade

[fatguy1992]

Thanks any newer builds? So that end up 2x 180watts @ -69C with smaller compressors then I would be using.

[Patrickclouds]

http://www.xtremesystems.org/forums/...ad.php?t=70265
but i don´t know if it has ever worked.

here are some pictures of that unit:
http://rapidshare.com/files/41184843...ap_cascade.rar

[sdumper]

Wait didnt kayl do one?


He is also in OZ right?

[SAE]

LittleDevil tried to do one, but got into problems with load balancing...
http://benchtec.co.uk/forums/showthread.php?t=525

[EliTE22]

easiest way would be two cascade in the same case.
how about a 3tons in the 1st stage and 3ton on the second with dual heads

[n00b 0f l337]

Sounds wastefully big.

[cdolphin]

3 compressors does sound like overkill!
Am I completely off basis, or are we talking about two evaporators in parallel? I imagine there would be difficulty if the load was different between the two heads, as the pressure differential would be different...
I hope this goes through! I would love to learn/hear about it!

[EliTE22]

fatguy what kind of load temps are you okay with?

[fatguy1992]

http://www.xtremesystems.org/forums/...ad.php?t=70265
but i don´t know if it has ever worked.

here are some pictures of that unit:
http://rapidshare.com/files/41184843...ap_cascade.rar

LittleDevil tried to do one, but got into problems with load balancing...
http://benchtec.co.uk/forums/showthread.php?t=525

Dam shame they never worked well.

Wait didnt kayl do one?


He is also in OZ right?

Yeah from memory he tried a 3 headed cascade, 1 CPU and 2 GPUs. It couldn't handle the heat load.

easiest way would be two cascade in the same case.
how about a 3tons in the 1st stage and 3ton on the second with dual heads

I don't really have that much money, hence why I'm wanting to re-use most if not all the parts I already have.

3 compressors does sound like overkill!
Am I completely off basis, or are we talking about two evaporators in parallel? I imagine there would be difficulty if the load was different between the two heads, as the pressure differential would be different...
I hope this goes through! I would love to learn/hear about it!

Heres a quick ms paint drawing of what i'm talking about not great but it should do...



Uploaded with ImageShack.us

fatguy what kind of load temps are you okay with?

I was thinking about 300-350watts each head in the -80c's.

[n00b 0f l337]

I wouldn't do it that way. Under that circumstance, should you not run one of them, you have a ton of wasted flow. Options are...
Either run two TXV's. Or, make one larger self-coiled heat exchanger. Something like 20 ft of 1/2" tubing with two 3/16" run through it. Then put a TXV on that.

[ultralo1]

Heres a quick ms paint drawing of what i'm talking about not great but it should do...



Uploaded with ImageShack.us



I was thinking about 300-350watts each head in the -80c's.

You have the two plate HXs in parallel. Thats is one big bi**h to load balance. Put them in series and drop in an accumulator between them and the compressor. It will save you some major head aches.

[n00b 0f l337]

You sure Ultralo? That doesn't seem like it'll balance them.

[[XC] gomeler]

Solenoids + PIDs are the solution



Just throwing something out there since we're all doing it.

[ultralo1]

You sure Ultralo? That doesn't seem like it'll balance them.

It doesnt balance them. It creates a bigger HX. You will have to do the brute force method. Balancing two evaps on the same system is hard, then if you put it into a dynamic situation, it is exponetially harder.

Here a few questions to ponder regarding the parallel setup:
1: How are you going to ensure that both metering devices are getting the correct flow?
2: How are you going to adjust superheat on each HX?
3: How are you going to ensure that each HX are responding correclty in a dynamic situation?
4: If using TXs how is one TX hunting going to affect the other TX since, suction pressure will be varying?

[sdumper]

Solenoids + PIDs are the solution



Just throwing something out there since we're all doing it.