Autocascade Discussion and build attempt

[Russell_hq]

My compressor has a maximum working pressure, so I dont want to go beyond that. So if I reach an R23 SST/Evap exit difference between 5-10K and my R290 SST/Evap difference is near 30K (EDIT and I am at my max working pressure), then I dont have any room to add more R290 without going past the max working pressure for my compressor. See what im saying? Anyway, here are the new temps after adding some R23.

R23
Evap Exit: -56ºC ( i added a little)
SST: -64ºC (1.6barg, 23psi)
SCT: -12ºC (16.6barg, 240psi)

R290
Evap Exit: 15ºC
SST: -18ºC (1.6barg, 23psi)
SCT: 52ºC (16.6barg, 240psi)

Air in: 22ºC
Air out: 26ºC

You can read what the manufacturer has written about the compressor, im guessing that the max working pressure is 25bara. What do you think?

http://www.cubigel.com/java/X?cgi=cu...rmaciontecnica

[Gary Lloyd]

The R23 looks just right now.

The heat exchanger is working very well.

Good airflow.

Looks like it could still use a little more R290.

It seems unlikely that the R290 cap tube is too restrictive, being 10 feet of .031, but autocascades are new to me.

What is the CPU temp?

[Russell_hq]

I removed the thermocouple from the front of the cpu and attatched it to the evap exit. So im using the motherboard to measure the cpu temp, its got a thermistor which presses against the back of the cpu. Currently its measuring -19ºC. This doesnt look good when the evap is boiling at -64ºC . Though I know that the evap works well, so I just dont trust the reading too much. Its more of a relative measurement I get from it.

The R290 is a strange one on me too. I just keep adding it bit by bit, but I cant shift the exit temps past 14-15ºC

[Russell_hq]

I went back and had a look at an old post. You can see what I mean about not trusting the temp it reports.
http://www.xtremesystems.org/forums/...052#post355052

I had a thermocouple right beside the core and my fluke was reading -37ºC (100% sure it wasnt touching the evap) while the motherboard was reporting -7ºC. Draw your own conclusions.

[Gary Lloyd]

The R290 is a strange one on me too. I just keep adding it bit by bit, but I cant shift the exit temps past 14-15ºC

This would be another indication that the cap tube is too restrictive.

What are all of the temps and pressures doing as you add the R290?

[Russell_hq]

R290 evap exit temp rises just after I add a little bit. Then it slowly begins to fall. I added a little bit then went for a shower and this is what I have got:

R23
Evap Exit: -55ºC ( i added a little)
SST: -64ºC (1.6barg, 23psi)
SCT: -11ºC (17.4barg, 240psi)

R290
Evap Exit: 17ºC
SST: -18ºC (1.6barg, 23psi)
SCT: 53ºC (17.4barg, 240psi)

Air in: 22ºC
Air out: 26ºC

Notice that the Evap exit has risen from 15-17ºC. Its definatly not dropping as I add more R290.

[Gary Lloyd]

The good news is that the high side pressure isn't rising, either. This may be the best we can get with this cap tube. I think we need to remove about 2 feet of the R290 cap tube. Better yet would be to replace it with a TXV.

Even with complete flooding of the R290 evaporator, I don't think the bottom line temps are going to get much lower without a larger compressor, but I could be wrong. Possibly a shorter cap tube would provide significant improvement.

[Russell_hq]

Thats what I was afraid of. Well im going to crank up the heat and see what happens As there is not much else I can do to the system, Im going to up the load and see where I can take it

[Gary Lloyd]

We also need to shut it off and warm it to room temp to see what the static pressure is. If it is too high, we may need an expansion tank.

[Gary Lloyd]

When you crank up the heat load, tell us all of the temps and pressures, so we can see what effect heavy load has on it.

[Russell_hq]

What's too high? What should I be looking for?

[Russell_hq]

Ok, I'm going to need more R23 in it to cope with the extra load.

[Gary Lloyd]

You are a long way from the 26 bar limit.

The ideal is to have 5-10C difference between SST and evap outlet with maximum load.

[Gary Lloyd]

We need to see the full list of temps and pressures.

[Russell_hq]

rgr that gary. heat load shoud now be in the region of 110Watts (from 68 watts). I will tune the R23 SST/evap out temperature difference to between 5-10K then report back.

[Russell_hq]

Gary, I was thinking about the R290 evaporator exit temperature. Should I be able to get this below zero and within 5-10K of SST with no load on the system? I say yes, but I dont think it will do it from what I have experienced of it so far, if thats the case can you conclude anything important from this that will help me get the temp down?

[Gary Lloyd]

It doesn't seem as if it is going to allow that additional flow with this cap tube size, and I don't think no load operation is going to do it. If anything, adding more R23 to tune the evaporator under heavy load may force a little more R290 through, but that seems unlikely also. Keep in mind that I have zero experience with autocascades, so I am learning too. I am waiting to see what effect the additional R23 has, as well as the heavy load. Have you added the R23 under heavy load yet? Do you have temps and pressures for me?

[Russell_hq]

Not yet. I should be getting some more thermocouples in the next couple days, so I can stick them to the system and see whats going on. I have 1 on the R23 evap exit and 1 on the R290 evap exit. Could you list in order of importance where you would like me to put the rest of the thermocouples, you can assume that I have as many as the number of temp readings you would like, thanks.

[Russell_hq]

Gary these are just for you before I go off to bed. I had to give it a good bit of head pressure by adding more R23 to get the Evap exit with 5-10k of SST,


R23
Evap Exit: -52ºC
SST: -63ºC (1.7barg)
SCT: -3ºC (22barg)

R290
Evap Exit: 18ºC
SST: -17ºC (1.7barg)
SCT: 64ºC (22barg)

Air in: 24.5ºC
Air out: 28.6ºC

CPU: -13ºC

The condensor in is hot and out is mild/cool (measured using my body thermometer ) thats the best I can give you at the moment.

[Russell_hq]

Checked static pressure this morning, its around 110psi with room temps about 21ºC.

[Gary Lloyd]

I've been going over all of the numbers, and everything keeps pointing to the cap tubes.

The R23 cap tube worked beautifully at the lower load, but we needed to add considerable pressure to push enough refrigerant through for the higher heat load. I think we need to shorten this cap tube a couple feet, which should give it roughly 40-50 watts more capacity (guestimating).

The R290 cap tube hasn't come close to flooding the heat exchanger even under minimum load with full sight glass, and doesn't budge no matter how much pressure is pushing the refrigerant through. The cap tube is much too restrictive. Not even in the ballpark. We need to cut off several feet. I would cut off 3 feet, at least.

I don't think we are going to have a problem with static pressure in this system. The minimum liquid R23 strategy seems to be working very well.

[Russell_hq]

Thats good news, I will try and get some cap tube cut off the system today and see what happens. And I will get back to you. 3 feet of the R290 and 2 feet off the R23. That will leave me 96" on the R23 and 94" on the R290. The original sizes where 120" R23 and 130" R290.

[Russell_hq]

I gave the cap tubes the chop, hooked it up to the computer and put 120 watt (approx.) load on it. Here is what I have:

R23
Evap Exit: -49ºC
SST: -59ºC (2.2barg)
SCT: -5ºC (21barg)

R290
Evap Exit: 18ºC
SST: -12ºC (2.2barg)
SCT: 62ºC (21barg)

CPU: -5ºC

As you can see I still have the problem with the R290 exit temps. I took 3 feet off the cap tube, and the sight glass is full.

[Gary Lloyd]

The R23 cap tube looks just about right.

The R290 evap has dropped the exit superheat from 35K to 30K, but it is still too restrictive. We are looking for 5-10K.

Just to get an apples to apples comparison, we might drop the load back down to 68W, and see how all of the temps compare.

[Russell_hq]

I like apples to apples. I was seeing how far I could push my cpu, just cant help myself Thats why the load was up.

I set up the cpu the same and see what we can do, what about the charge, do you want me to get it in any pressure range?