Im extremelly happy for your input aenigma...
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First off, use 2 filters, one on each liquid line.
Noted
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You dont "need" a solenoid on the 2nd stage discharge line, just charge the system with only r22 and test it thoroughly to make sure there are no leaks and to be sure it works well.But if you use one then you wont have any load on the interstage when adjusting superheat.It will help to test unloaded and loaded conditions(when open and feeding r22 into interstage), so it is favorable, though not mandatory.I would prefer leaving it open so I could test the system with the interstage being loaded by the r22 condensing in it.
I hope you understand my way of thinking:
When the interstage is cutted off only the R22 part of the system works, cooling of the R23 stage to lets say -40C unloaded. Now, opening the soleneoid causes R22 (when theres no R23) to rush in a -40C area filling that part of system completelly (when the injector on the evap is closed), so theres a crazy heat load for a moment, no condensing in the condenser, just the hx, the hx fills up (acting as the cool side of a heatpipe) and nada, no heat load, just more R22 in the system.
If the injector on the evap is open i see a different problem. Beacause theres such a cold space R22 stops condensing in the condenser, now it has a colder space to do that. The system starts cycling, HX filled up, heats up, condenser starts to work, feeds R22 to the TXV, HX cools down, theres a much colder space in the system (thx hx), no freon to the txv, hx fills up and again, and again...
I cant see it acting as a subchiller, the TXV has a too high throughtput, the HX is to efficient, i dont thing it will work that way.
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Since it will use a txv you can do the real fine tuning once the 1st stage is working properly and you are ready for the 2nd stage.Txv's are very forgiving, and when it is charged correctly you wont run the risk of starving the evaporator like you would with capillary.My method would be to make sure the 1st stage is working perfectly then turn the system off and let it sit until it is at ambient and static charge the r23 to a low safe pressure(probably 80-125psi) and then start the system closely monitoring pressures so they dont get too high.If all goes well then you can monitor all your temperatures and start fine tuning.
Thats what i planned... But i dont thing that the R23 static pressure will be that low...
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Since youre using a txv then you dont need to subcool the liquid line unless you want to lower the temperature of the liquid entering the evaporator.But I see too many drawbacks to make it viable.The obvious drawbacks being more insulation and having to make a new tube in tube heat exchanger with very small returns.And it would increase superheat quite a bit depending on how efficient it is.I just dont think a suction/liquid heat exchanger is worth it on a txv system that is fed 100% liquid vs. capillary that feeds vapor/liquid and really benefits from subcooling.
Noted
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One more thing, why do you say you dont have enough compressors?It seems you have 3 of them, i'd say that is enough for a cascade system that only needs 2.
The oil in those compressors is incompatabile with R23 (needs poe) and i need to change the oil. The problem is the fact that i can get only ~30-50ml out in the begening. When i added 300ml of mineral oil to one of the compressors - not even a drop came out. Any good ideas ? IF theres a nice way to get rid of all the oil in these compressors and change it nice and clean - full blown cascade here i come.
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You need to start small with a basic cascade system before trying autocascade.If I remember right you already tested your old cascade and it didnt work right with r22 on both stages.
the latest news would be: "works fine, now i need to change the oil in the II stage compressor so its R23 commpatabile". Calibrating a system with injectors is dead easy, fill it up so the injector doesent starve and change the frequency / pulse lenghts
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Now youre trying to go into a full blown r23 autocascade system, I would recomend against that.
I also dont like that idea, unless a miracle happends ill probably be left with no alternative...
Maybe you wondered why i am so stubborn- i like doing such things, the harder the better... I have few other projects being completed exept this one, like finishing a gas turbine wich will be a jet engine in its first form, later im going to convert it to a turboshaft engine and power a diy gokart...
