After months of planning and research I took the plunge into autocascades.
Compressor: 1/2HP Rechi Rotary
Condensors: 2x 10x10 two-row condensors in parralel
Phase Seperator: 12" long 1" diameter copper pipe with endcaps and copper wool
Suction Line Heat Exchanger: 10" liquid/gas HX, can't remember the manufacturer
Heat Exchanger: 12" long 1" diameter copper pipe filled with 7 10" long 1/4" copper pipes connected in parralel.
Metering Devices: 7' of 0.031" cap tube for the evap and 8' of 0.031" of cap tube for the HX
Filters: 2x liquidline filter/dryers for installed before each cap tube.
Fan: 12" unducted fan cooling compressors and condensors.
Static Pressure: 97 psi
Unloaded Pressure: 210 psi high 40 psi low
Safety: 325 psi electrical cut off, 375 psi valve
It took me a while to figure out how to tune this system, the amount of volume compared to a single stage made it rather difficult when I dumped roughly 20 ounces of propane into the system to get the proper HX temperatures. I made a mistake in the HX captube, on reflection it should be much shorter, think I'll cut off 18 inches next weekend. I don't know if my system was just terribly thought of but I can't get the HX to drop below -20 celsius and the evap to drop below -56.5.
Pulldown time from system at ambient to -56.5 on evap takes about 10 minutes. The worst part is the drop from 31 celsius (ambient today) to 5 celsius takes a good 7 minutes then it snowballs to -56.5 celsius. On startup discharge pressures spike at 255 PSI on immediate startup and drop down to 210psi within the first minute. Power consumption peaks at 540 on immediate startup and slowly drops down to 460 watts with a 35 watt fan included. I think that just about covers it, diagram of the system along with pictures below, it isn't pretty but I think it's pretty good for a first job and a test system.
Future ideas to be applied will be:
Wrap r290 captube around the suction line
Pipe the evap gases into the HX rather than bypass to SLHX
Larger HX/Plate HX
Better gases, r1150 and/or r170.
Better tuning techniques
Sorry about the crappy pictures, I only have a camera cell phone, 1.3MP doesn't cut it.
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Good to see you're using a cut off switch as well as a release valve. Walt will be proud.
Nothing wrong with that for a first auto cascade. It will only get better
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Originally Posted by kayl
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Originally Posted by DetroitAC
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Well I managed to get temps down to -59 celsius by venting some of the r290/r744 and then charging with r744 to bump up the r744 content in the loop. Now my static pressures are at 210 psi, operating pressures are 35/230, and it pulls down to the -5x rather quickly but that final creep to -59 takes forever. Done toying with it now, need to get a loadtest on it and see how it handles that first. The captube lengths were definetly the weakspot, I just went with I thought would be decent lengths, I actually thought they could be too short, especially on the evap. Apparently I need a more restrictive system. Wish I had a way to view the inside of all the pipes to see if I'm overcharged on CO2, undercharged on propane etc w/o having to install 5 sight glasses.
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Luke you also use quite a bit stronger compressors. These are like 9cc rotaries. I think he does need more r290 though. And better capillary sizing.
And Ron,
Quote:
Originally Posted by Gomeler in post4
Wish I had a way to view the inside of all the pipes to see if I'm overcharged on CO2, undercharged on propane etc w/o having to install 5 sight glasses.
I'll have to retune it when I get a dummyload onto it, will have start over which is a shame as there is more than a pound of r290 in it. Guess it's time to hitch a ride to refill my cylinder, never thought I'd see the day. Was never expecting amazing results with this system, next one will be a step above with much more attention paid to the cap tube sizing as I just ordered a 100ft spool of the stuff, no more 10ft limitations from Supco.
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Gom can you PM me the link to where you ordered from?
I Think you'll see most of your improvement by adding 2 feet of captube, and though I can't see what your HX's look like, maybe neatening up a bit (i know its just a test system) and improving your HX's.
The 100 footer? I ordered at my local United Refrigeration, the guy gave me a 5 finger discount Once I have the spool in hand (10 days as it's being shipped form chicago) I'll tweak my captube. Final cost is going to be ~$32 for the spool I think, check your local HVAC stores, if anything I could ship you a spool if you can't get it for any cheaper + shipping locally.
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a friend of mine have a problem on tuning R744 autoc system, usually dice is formed in the captube causing a sudden increase in evap temps. do you have this problem too? how do you tune it?....
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a friend of mine have a problem on tuning R744 autoc system, usually dice is formed in the captube causing a sudden increase in evap temps. do you have this problem too? how do you tune it?....
adding more, more, more and more R290 in to the system.
nope, no dice in the lines yet, the temps just plateau at a point and flucuate +- 0.1 celsius. Just a terrible tune + incorrect captubes are my problem. Store that sells the wirebound resistors I wanted to buy is closed, will have to wait till tomorrow
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I want to attempt something similar myself this summer, so I would love to see your results.
If ya need some more info on autocascades have a look at this forum, it has ppls builds on autocascades from the last previous competitions. http://www.teampuss.com/forums/index.php
Also an actual autocascade section as well. Lots of good stuff in there hey.
How are dice geting into your system? Playing yatzie while building?
Or do you mean Dry Ice
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If the evap captube is only 7' i'd add 2 feet to it. It's a bit short.
Walt will be proud. 
Once I have the spool in hand (10 days as it's being shipped form chicago) I'll tweak my captube. Final cost is going to be ~$32 for the spool I think, check your local HVAC stores, if anything I could ship you a spool if you can't get it for any cheaper + shipping locally.
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