Cold Enough Cascade

[[XC] gomeler]

After playing around with SDumper's NCE 3 stager, I've decided to assemble a luxury benching 2 stager. After our experience with both of our QX9650's experiencing CBB at -70C to -90C and CB at -135C, I've decided to build this cascade so the operator can swiftly cut refrigerant flow to the evap to boot the PC and then flood the evap to get down to operating temperatures.

I also plan on attaching a small resistor to the backside of the evaporator and a low watt heating element stringed along the suction-line so the operator can gently warm up the suction-line and evap from -95C to a comfortable 15C to avoid cracking the cold suction line and having condensation issues on the evap on dismounts.

The system will feature two solenoids controlling refrigerant flow past the oil separator. One solenoid will control the oil/r290 return flow to let the user manually shut the oil return loop for the lowest evap temps and the second solenoid will control the R1150 flow to the evap, letting the user cut the flow. I need to contract/find a circuit that will not permit both solenoids to be shut otherwise the discharge pressures will skyrocket. I've decided to use solenoids so the user can have a single control panel to manipulate, eliminating user interaction with the actual unit via mechanical valves. This will also keep me from having to touch very cold valves, I don't fancy touching a -40C valve :down:

I plan on having 4 k-type probes installed into the unit itself. HX inlet, HX outlet, evaporator, and suction-line temps. 4 pressure gauges will be installed, suction/discharge on 1st stage and suction/discharge on the 2nd stage. The HX temps will let me know when to fire up the 2nd stage and how well the 1st stage is holding the 2nd stage. The lineset probe will be good for thawing out the unit and the evap is standard.

The 1st stage will feed the plate HX with dual 7' 0.031" capillary tube lines, the oil return on the 2nd stage will use a 8' 0.031" capillary line, the 7 liter remote expansion tank will use a 10' 0.031" capillary line, and the evap will use a 7' 0.031" capillary line.

The unit will use staggered safety features with the 2nd stage including a 425psi burst valve and two pressure cutouts at 300psi and 350psi. The 1st cutout will force both solenoids open, the 2nd cutout will cut power to the entire unit, and in a worst case scenario the burst valve with vent the R1150 charge downwards into the base of the unit. In theory this will remove all ignition sources and prevent ignition of the R1150 charge. The 2nd stage should never see pressures above 225psi though, safety first though :up:

This will be my nicest and most advanced build ever. I know a lot of people build cascades in their spare time, but for me this will be both my review/bench cascade and my entry into the -100C club. After playing with my baby cascade and SDumper's NCE I've figured out exactly what I want in a cascade I can use for 12-18 hour stints. I hope to be able to run the rotary compressors close to their rated compression ratios to help with the noise, I want ease of use in setup, operation, and shutdown, and I want an oversized condenser/DSH to permit lower speed fans and lower noise operation.

Put a lot of thought into this build and I've accumulated most of the parts. Over the next week I'll start to slowly assemble this build, I want it to be a work of art :cool: If you have any criticisms or suggestions, please let me know. This will be my first foray into R1150 cascading besides tuning the NCE, all advice will be welcome.

[ruffus]

that sounds like a good little project you got going can't wait to see the build and keep up the good work

[Moc]

Hey Gomeler,

I don't think you want to return the oil/R290 through the SLHX.
In such units, the superheat is quite low so the SLHX will be cold (-> boil liquid ethylen), too cold for the oil. So better let the oil as near as possible back into the suction line.

2) If your first stage is strong enough, I would recommend to solder the SLHX as I painted in the picture. With that, you get the ethylen colder. If you do it like you painted, you just unload the first stage and get a very high superheat in the second stage (which gives you very high discharge temps).

[[XC] gomeler]

Thanks for the advice Moc. For #2 I typically wrap the capillary tubing around the suction line, just kept it separate in the images ease of clarity. I just wanted to do something with the little R290 that would be flowing through the loop, not too worried about suction pressures as I want them around 5-8 psi under load.

Perhaps I could use the R290 to desuperheat the R1150 charge between the oil separator and then plate HX. I could then chill the liquid R1150 after the plate HX with the R1150 suction and then merge the R290 and R1150 suction lines. I'm just worried about having too large of a R1150 liquid line and resulting in very high static pressures.

I hope that by utilizing the R290 and warming up the R1150 return gas I can keep the suction pressures up around 5-8 psi and the discharge pressures around 160 to 170psi. I know it isn't near the 5:1 compression ratio recommended for rotaries but it's better than running them 10:1 or 15:1 just for a -105C evaporator.

[n00b 0f l337]

I just love the name, good luck, need anything ask Gom gom :rofl: :ROTF:

[DetroitAC]

gomeler;2900025'] I need to contract/find a circuit that will not permit both solenoids to be shut otherwise the discharge pressures will skyrocket. I've decided to use solenoids so the user can have a single control panel to manipulate, eliminating user interaction with the actual unit via mechanical valves.

That part is easily and cheaply done with a little relay logic.

First, the button or switch for a solenoid is a double throw momentary action type. The first set of contacts actuates the solenoid, and the second actuates a relay that opens the solenoid circuit of the other valve (so that if the button is pressed, the circuit will not be completed).

Then you do the same thing for the other button/solenoid. If you press both at the same time, they will open each other's circuits and no solenoids will actuate.

[Clemmaster]

SLHX on second stage isn't a good idea, the load in the HX increase very fast with ethylen and so does the suction specific volume at low suction pressure and moderate temperature. You'd need a stronger compressor on first stage.

On first stage that's usefull with R507c/R404a beacause that's easy to set a big air-condenser but you need a stronger fan to cool the compressor.

[[XC] gomeler]

That part is easily and cheaply done with a little relay logic.

First, the button or switch for a solenoid is a double throw momentary action type. The first set of contacts actuates the solenoid, and the second actuates a relay that opens the solenoid circuit of the other valve (so that if the button is pressed, the circuit will not be completed).

Then you do the same thing for the other button/solenoid. If you press both at the same time, they will open each other's circuits and no solenoids will actuate.

Reading through that, it sounds like I'd need 2 energized closed solenoids and if I tried to close them both they'd cancel each other out. That might be the best solution if I can bite the cost.

Decided what I'll do is 1 energized closed and 1 energized open solenoid. The energized open solenoid will go on the R1150 liquid line and the energized closed will go on the R290 line. This way the R290 line will remain open if power is cut letting the unit equalized and the R1150 will close, hopefully keeping any oil from making it into the evap upon equalization. The biggest problem I have is the price of the solenoids, $90 for the energized closed and $45 for the energized open. If only those energized closed weren't so expensive, I'd use two of them. Might still bite the bullet on it, need to search around.


SLHX on second stage isn't a good idea, the load in the HX increase very fast with ethylen and so does the suction specific volume at low suction pressure and moderate temperature. You'd need a stronger compressor on first stage.

On first stage that's usefull with R507c/R404a beacause that's easy to set a big air-condenser but you need a stronger fan to cool the compressor.

Not sure if I am understanding this correctly. After thinking about it, I won't be plumbing the R1150 into the SLHX. I guess I'm not understanding why I can't use the liquefied R290 to chill the gaseous R1150 before it hits the HX? The R1150 vapors should still be around -70C by the time they hit the compressor I imagine as I will only be wrapping the R1150 capillary tubing around the suction-line so those will stay relatively dense. What little R290 is in the loop will be oil saturated and I didn't want to shoot liquid R290 into the R1150 stream and not have it completely boil off and slug the compressor. Does that make sense or am I thinking about this wrong?

[DetroitAC]

Hmm, I don't see why you couldn't use either type just change the relay logic to suit. The real dilemma is the power usage and annoying buzzing noise. You would want the state that the valve is in the majority of the time to be de-energized.

[[XC] gomeler]

Hmm, I don't see why you couldn't use either type just change the relay logic to suit. The real dilemma is the power usage and annoying buzzing noise. You would want the state that the valve is in the majority of the time to be de-energized.

Well I wanted the ones that when energized would close so that while benching they would mainly stay de-energized. I figure this is better so that the system pressures can equalize without any power to operate the solenoids. I liked this option more than having to keep the solenoid powered on post-shutdown to equalize the pressures. Nothing is ever easy :p: How much power do the solenoids consume in their energized states? I figured the coils couldn't be too many watts.

[{.bLanK} GoD]

Relays don't buzz. And the power usage of the relay coils is 5/8ths of f**k all compared to a couple of compressors.

[Clemmaster]

gomeler;2900025']
I also plan on attaching a small resistor to the backside of the evaporator and a low watt heating element stringed along the suction-line so the operator can gently warm up the suction-line and evap from -95C to a comfortable 15C to avoid cracking the cold suction line and having condensation issues on the evap on dismounts.


That's not a good idea neither :p:. Compressor's Isentropic efficiencies are between ~0.5 and 0.7 (for those we use). With a suction pressure of 1bar and a 20°C gas enterring the compressor you get an exit temperature (right after compression) of more than 220°C ... I don't think oil will like such a high discharge temperature :p: The volumetric efficiency will decrease very fast with increasing suction temperature, especially at low suction pressure.

[DetroitAC]

Well if you hafta leave them energized, then you hafta. Solenoids are the annoying buzzy ones :yepp:

It's just a standard practice that I'm speaking of, you (usually) have solenoids engaged the least amount of time possible. Usually it's just as easy to have them going normally closed or normally open, so the default design is the one that uses the least amount of electrical power. For stationary equipment with heavy usage, the cost of electricity over the life of the solenoid valve is important. If you just can't do it that way for safety or operation reasons, then oh well :shrug: you can't

[mytekcontrols]

Well if you hafta leave them energized, then you hafta. Solenoids are the annoying buzzy ones
I use sporlan solenoids (B6, B9, custom XUJ). Never had a problem with buzzing (maybe all those years of blasting the music in my car have caught up with me). All I hear is a sharp click when engaged, and a thunk when released. What make of valves are you referring to?

Hey Gom looks like a great project :up: And I agree with the logic of having the valves open when non-energized. Keeps it safe that way.

Look forward to seeing the evolution of your new unit.

[DetroitAC]

Sporlan E5, although I've also got a lot of water solenoids around and they are they same way. If the coil is being held just right you won't hear the buzzing.
Maybe yours are close enough to the compressor that it drowns them out? My Bitzer compressor skid is on the roof, and the valves are in an insulated climatic chamber in the lab. It's a matter of perspective, I suppose but to me they are loud.

edit: now that I think about it, Gomeler will have them right close to the compressor, so probably no big deal.

[[XC] gomeler]

Not too worried if they buzz like the little solenoids I used in my Phys2 class. They'll easily be drowned out my the compressors and condenser fans. Thanks for the info guys :up: Parts are all ordered besides the main condenser, now I play the waiting game with UPS/Fedex.

[[XC] gomeler]

Decided to simplify the build a little bit. Going with a single valve on the 2nd stage that will cut refrigerant flow to the evaporator. I couldn't stomach to pay $110 for a normally open valve+coil so I went with a single $40 normally closed valve + coil that will cut the R1150 flow. The oil separator will be cap-tube fed so the entire system will have a way to equalize as that was my largest concern.

I'm in the process of getting a quote for my condenser and contracting out the case for this build. I'm going to have the condenser, 4 pressure valves, and the high-pressure cut-off all visible on the front of the case and then vents on the backside for exhaust airflow. Think I'm going to go with 24 gauge aluminum for the case and the case will bolt onto a supporting base with protruding handholds for easily maneuvering. I've only got 2 pieces restricting the case size, I want it to fit in the backseat of a normal car, and it's got to be as wide as the condenser. Parts start showing up on Monday so I'll start laying this sucker out and maybe get the 1st stage assembled by Wednesday.

[[XC] gomeler]

I haven't forgotten this project, I actually just finished assembling it. I tossed in a rough tune of r290 on the 1st stage and r1150 on the 2nd stage. It's been running fine but the condenser I used on the 1st stage is much too small. Unfortunately I'll be out of town for the next 2 weeks so I won't have a chance to post any big shots/scores till afterwards. I had it idling at -106C for a little while but the undersized 1st stage condenser is really crippling the unit. Going to get a Chilly1 Big Blue if I can get a hold of him. Back to blasting my HD3850's :cool:

edit: oh yeah, right when I finished the unit I realized a tragic error in my design. Using the solenoid to cut off the flow through the HX without a low-resistance path for the refrigerant causes the high-side on the 2nd stage to shoot up very quickly as it just heats up and compresses the R1150 and pushes it through the oil return loop. I'll be re-building this by plumbing in the solenoid after the oil separator on the R1150 side and with a 1' piece of capillary tubing I'll dump the R1150 into the suction side, hopefully bypassing most of the evap and helping to control temps without introducing oil into the evap.

[sacha35]

Sounds like a nice build gomeler, what size are the compressors that you will be using?
It should work out very well with the Solenoids providing you put in some kind of safety switch so that they cannot be closed or opened by accident.

[[XC] gomeler]

Well I'm just going to have the bypass and it'll be normally closed. 11,000 BTU on the 1st stage and 8,000 BTU on the 2nd stage. Once this condenser is swapped out this thing will positively howl :yepp: