Morphing Air Conditioner into Autocascade System

[kang-China]

and what about danfoss in the USA

if i want to buy some SPORLAN what can i do

[wdrzal]

KANG-CHINA........Mytek controls auto-cascade thread is in the stickies for the wealth of information it provides. It's already a very long thread and Mytek provided as much information as he determined appropiate.

Many of the questions you are asking are REDUNDANT. You may want to read the thread severial times but also read all posts Mytek made and all the threads Mytek contributed too. That should be a years worth of reading.

I can't speak for Mytek but doubt he has the time to answer the same questions over again.

Also Asking Redundant questions in a already very long "sticky thread" makes it more difficult for other readers to find the important information they seek.

So Kang-China why don't you start your own thread on what ever topic you want to call it ("my auto-cade") and ask the questions there.

Walt

[mytekcontrols]

Ditto

[n00b 0f l337]

Note(1): It would seem that the "Stepper" design that I see being used for CPU cooling, has proportionately more surface being cooled on the circumference then on the CPU side. This seems like a waste of material and extra machining. Where as a low profile design would seem to be more efficient.

Note(2): Has anyone measured the surface temperature versus the refrigerant temperature of any of the currently used evaporator designs while under full load? If not, then how can anyone know if a given design is any better (or worse) than another?

Well, to 1, I can see what you mean, but I think we've always gone with the assumption that heat transfer will as always follow to the cold dead zone, so making the entire evaporator cold would be sufficient.

As for two, I've tried to use matching setups with different evaporators. Ultimately other then expansive, I found the worst evaporator to be a simple cap in cap design, moving up a gradient to a Chilly1 spiral (which we've known to see fail at larger loads), then to a stepper and finally to an Eleven style (like a pin grid or spiral on the CPU side). So it would follow as you said, but the machining time I think has always been the killer.

[mytekcontrols]

Hmm... Nol I wonder if we should also move this evaporator talk to another area, although I do find it fascinating, but its relevancy to this thread may be somewhat questionable. I think there was an ongoing thread about evaporator designs, perhaps we can find it and move this discussion there.

What do you think? Can we copy and paste this stuff over there?

[n00b 0f l337]

Not a bad idea.

[kang-China]

hi,mytek

please tell in your AC-2,and AC-3,about the compressor oil

POE or AB ,or another,,

thank your

[Kevin Hotton]

I would suspect that iso-pentane is the best substitute for R-123 both have a 1-atm. boiling point of 27C. The use of n-butane throws the refrigerant balance off.

[Kevin Hotton]

Yes it should be. In fact Polycold has a system called a PGC-150 that utilizes this many stages, and the same refrigerants (although it does have a subcooler and small amounts of R-14 and Argon as well). It does -120C at just over 300 watts, and utilizes a 1 1/2 HP reciprocating compressor.

But if you are just starting out with autocascade design, it is better to keep it simple, and build up from what you learn.

Edit: the PGC-150 also uses Ethane as part of its blend.

I reviewed the link for the PGC-150 and it states rated amps 12.5 at 230VAC (2875W). Even with the air-cooled condenser fan, this seem way over 1.5-hp (1.5*750/0.85 = 1324W, the 0.85 is the electric motor efficiency). So it appears to me closer to a 3-hp used by this reciprocating compressor. What am I missing?

Kevin

[wdrzal]

I reviewed the link for the PGC-150 and it states rated amps 12.5 at 230VAC (2875W). Even with the air-cooled condenser fan, this seem way over 1.5-hp (1.5*750/0.85 = 1324W, the 0.85 is the electric motor efficiency). So it appears to me closer to a 3-hp used by this reciprocating compressor. What am I missing?

Kevin

A good quality hermetic compressor can be pushed to 200%++ of their rating. They might only last 3 to 5 years (instead of 20+)before the insulation on the windings breaks down. Look @ NEMA motor insulation classes.

Walt

[mytekcontrols]

A good quality hermetic compressor can be pushed to 200%++ of their rating. They might only last 3 to 5 years (instead of 20+)before the insulation on the windings breaks down. Look @ NEMA motor insulation classes.

Walt

Walt is correct. When this system was developed, the compressor was pushed very hard in order to meet the desired specification of -90 to -95C for a secondary gas outlet temperature @ 12 CFM flow rate (this is the equivalent to 850 watts of total heat load). However in an autocascade such as this one, the better suction cooling provided by the choice of refrigerants in use helps to compensate for this greater current draw by providing better heat transfer as opposed to a single refrigerant system. The only down side was difficulty in starting under low voltage conditions.

Edit: The PGC-150 was a gas chiller, meaning that it consisted of both a primary and secondary circuit, with the primary side being an autocascade refrigerated system, and the secondary being a gas loop cooled by the primary circuit. The secondary gas circuit could be a flow of nitrogen gas or supplied by a clean dry source of compressed air.

[Kevin Hotton]

Michael based on your description, I guess thermodynamically, the PGC-150 is not quite as impressive as it first might appear. Because it is cooling a gas from room-temperature down to -95C and uses the paralllel cooling path with the autocascade return refrigerant flow, it provides very little of its total cooling duty at -95C. To cool nitrogen to -95C there is no phase change so it is all sensible heat with an effective heat-transfer temperature of probably only -50C. It would be much harder (probably impossible) to match the PGC-150's COP if you had all the cooling being done by an evaporator at -95C. If all the cooling was done at -95C, it COP would likely be cut in half.

Kevin

[mytekcontrols]

I'll respond to this here, but this is getting very off topic from the original theme of this thread, which is suppose to be about converting window AC or it's components into a working autocascade refrigeration system.

Michael based on your description, I guess thermodynamically, the PGC-150 is not quite as impressive as it first might appear. Because it is cooling a gas from room-temperature down to -95C and uses the paralllel cooling path with the autocascade return refrigerant flow, it provides very little of its total cooling duty at -95C.

The process of cooling the secondary gas stream from a +25C ambient down to a -95C outlet (an effective change in temperature of 120 degrees) is a gradual process due to the parallel path the secondary gas cooling circuit takes with the autocascade's primary mixed refrigerant stream. To say it provides very little of it's cooling duty at -95C is probably accurate to some degree, since the responsibility for cooling is not simply isolated to one HX. And the bulk of the cooling is most certainly happening in the first two HX's, which is very typical for a 2 phase separated AutoC (Auxiliary Condenser - Phase Sep#1 - Cascade #1 - Phase Sep#2 - Cascade #2 - Sub-Cooler - Evap) whether it be a gas chiller or not.

It would be much harder (probably impossible) to match the PGC-150's COP if you had all the cooling being done by an evaporator at -95C. If all the cooling was done at -95C, it COP would likely be cut in half.

Yes that is the point of spreading the cooling of the secondary gas stream across the entire AutoC's HX stack. That being to increase efficiency. This same method would work equally as well for a liquid chiller.