Howdy...

[Mark C]

Howdy. I just thought I'd check in and introduce myself, as i just stumbled in here. Are any of my friends here??

[Dan]

Howdy yourself, Mark. I think you will be pleasantly surprised. Try using the search function.

The edit function is also a nice thing.

[Andy]

Howdy Mark,
nice to hear from another Nh3 technician Hope you find somthing of interest to you on this site.
Regards. Andy

[Mark C]

Hi, Andy....

Actually, I'm not a "technician". Which I take to be a service technician here in the USA. I'm a design engineer. Although in my formative years, I did servicing and rebuild of compressors and systems, I no longer really do those chores.

I design (new and additions), troubleshoot, and work on OSHA/EPA compliance issues. I also teach, having taught Industrial Ammonia Refrigeration I & II at a college in California for four years. I also teach custom training courses and RETA review courses for clients in their facilities.

My shingle is hung at www.coldprofessionals.com , where you can find my resume if you are curious.

...Hey, It's a living!!

[Andy]

Hi Mark C,
still nice to hear from you, even if you no longer work at the sharp end
With a designer on the fourm I will have to talk more sense from now on

The big thing in Industrial Ref in Europe at present is co2 systems (R744) is their any great amount of them in the US yet?
Regards. Andy

[Mark C]

Not really, just specialized installs. One had to be removed, several years ago because it was considered dangerous as the people that worked on the ice cream line keep keeling over... Maybe you are talking enclosed systems??

I doubt anything will replace ammonia as the choice in warehouse distribution and food production.

[herefishy]

Hi Andy,

Are y'all recircin' Co2 as with a compressor in a closed system? Enlighten me. I'm interested in cooling CPU's with CO2. At first shot, I thought I would just build a block and expend the CO2 and see if I can get -78F.

[Gary]

Why -78F?

[Andy]

Hi all,
the R744 systems we are now installing replace the large sector NH3 systems. The main differances ofcourse are the pressures, strength tests are preformed to either 52barg or 70 barg, dependant on system allowable pressure. We recently installed a R744 system in a distribution center for a supermarket chain, installed duty was in the region of 2500kW (slightly more actually).
The way the system works is the co2 is compressed by the low stage cascade compressors and discharged into a welded plate and shell heatexchanger, which is the co2 condenser and the NH3 high stage evaporator. The high stage plant is a coventional NH3 flooded plant with an evaporation of about -7deg C to give a glycol condensing temp of -5deg C.
The co2 is also used as a volatile secondary to cool the chill rooms.
Basically the liquid from the co2 condenser is returned to the co2 liquid receiver, where it is pumped thru the high temp coolers without expansion and returned to the receiver as a gas/liquid much as in a large pumped NH3 system (the gas is condensed in the co2 condenser again).
Mark C
the R744 refrigerant is safer than NH3, with a threshold short term exposure limit of over 300ppm, with no long term effects. As with any gas a leak detection system is needed, how many sailors have been killed with something as harmless as R22
R744 is a lot safer than NH3, leak detection is easier, the only thing holding it back is lack of knowledge.
Herefishy
co2 is a high pressure refrigerant, and as such components are not readly available, especially in the size you need. You could run a R404a system at -50, to cool the co2 to -48 degC, but then why not just use R404a.
Also co2 is a soild at atmospheric, if you just alow it to go to waste, control is necessary to stop the pressure dropping too low, creating dry ice.
Regards. Andy

[Gary]

Hi Andy,

I think what herefishy has in mind is using CO2 for refrigerant in a cascade low stage for overclockers. I considered building low stage add ons for people with chillers capable of -30C or better.

But then, I have to keep reminding myself that I am retiring.

[Andy]

Hi Gary,
it could be done, but you would have to keep the temp down permantly in the co2, or vent off thru a releif valve as the pressure increased. What is the design max on a R404 pot, assuming you could get a small enough one, any compressor on co2 has a lot more capacity. If you did obtain a pot small enough, the motor would probably not be fit to drive the comp. The best solution would be a very small heat pump compressor (danfoss makes one I think) Oil won't be a major problem, as more viscos oil is needed with R744 anyway, a deep freeze or medium/low temp minerial oil would suffice.
My problem is obtaining R744 screw compressors small enough, the smallest Grasso "C" will do 300kW at -48 deg C -5 Deg C condensing.
I wish you luck Herefishy, as components are not yet widly available.
Regards and kind thought at all times Andy

[Gary]

The low stage system is vapor charged, at room temperature, with the system off, to 100-150psig. That's the highest the pressure can go when the system is off, because no liquid is present.

If this isn't enough refrigerant for the system, then the inner system volume is increased by using a storage tank.

Also, the low stage is never allowed to run until the high stage is down to temperature (about -30C SST or lower).

Therefore, the highest pressure experienced is SCT while running. About -20C SCT or lower.

[herefishy]

Oh.... Cascade... I see

I work on small cascades in the semi-conductor industry, here in Texas silicon Valley (Austin). I've charged a sceond stage Ethane circuit before according to factory spec ('am familiar with the vapor charge scenario). I would be embarrassed to tell you from what the necessicity of servicing the stage two was, though !

PS... that was a long time ago

I can readily obtain refrigerant grade ethane, however, would I need to get a grade of CO2 for the refrigeration application also? I guess not much research would be necessary.... I'm thinking that I just couldn't use food grade CO2 such as that used in soda pop.

The reason that I say -78F, is according to a resource that I found, that is the boiling point of CO2 at atmosphere, I assumed. As such my original thought was, if I can get -78F, why worry about all the compressor cr*p. The question is, how long would a 20# bottle last you?

But Gary..... I was initially thinking of just blowing the CO2 to atmoshpere, evaporating in the cooling block

[Gary]

It seems like dry nitrogen would be a better choice for expending, although I haven't worked with either as refrigerants.

BTW, lessons 12 and 13 in my book cover cascades.

[herefishy]

thought about nitrogen too... but you can't get liquid nitrogen in a self-contained bottle... I beleive

"liquified" CO2 is readily available in a bottle without refrigeration of any sort to keep it contained.

...You're gonna get a purchase out of me aren't you?

[Gary]

...You're gonna get a purchase out of me aren't you?

I'd give it away, but these damned bills keep coming in. And there's this food addiction I need to support.

[herefishy]

Originally posted by herefishy
thought about nitrogen too... but you can't get liquid nitrogen in a self-contained bottle... I beleive

"liquified" CO2 is readily available in a bottle without refrigeration of any sort to keep it contained.

ooohhhhm so now we're playin' the guilt trip card...

Anyway, I have been wondering, lately... were you employed by Trenton Refrigeration Products...?

..The Trenton Michigan thing, ya' Know... Did you know Glenn Schendelbeck?

[Gary]

Ubetcha.

No.

And no.

[Mark C]

Originally posted by herefishy
Oh.... Cascade... I see
The reason that I say -78F, is according to a resource that I found, that is the boiling point of CO2 at atmosphere, I assumed. As such my original thought was, if I can get -78F, why worry about all the compressor cr*p. The question is, how long would a 20# bottle last you?

Simple calculation of the watts your chip pulls and the BTU content of the evaporation of the CO2.

[Gary]

I can readily obtain refrigerant grade ethane, however, would I need to get a grade of CO2 for the refrigeration application also?

I've been looking through some old cascade manuals and here's how it seems to go:

R13 beats CO2. Ethane beats R13. Ethylene beats ethane. R14 is the king of the mountain, but it takes three stages to get there.

R13 is recommended down to -100F.

Ethane is recommended down to -125F.

Ethylene is recommended down to - 150F.

R14 is recommended for -200F and beyond, with ethane or ethylene for the intermediate stage.

None of my books recommends CO2.

[DaBit]

Originally posted by Gary
None of my books recommends CO2.

When everybody goes left, the probability of you going left too is higher than 50% (I just don't want to say that you will go left too )

This might be as well our CO2 problem. Nobody used it for a long time due to chlorinated/fluorinated alternatives being pushed during training ans school. Experience has gone, while experience with alternatives increased. Then, the next step is to say that the alternative is 'better'.

There are a lot of success stories which all needs investigation to find out if CO2 performs like it should. Besides: hydrocarbons suffer from the same problem.

[Andy]

Hi Dabit
Hydrocarbons too are not being exploited enough. At present we are installing a large MW polypropelene plant at an oil refinery. These petro chem people look at gases and select for best fit. Having more dangerous hazards on site the Zone 1 plant is not a problem. It is just fitted away from other buildings in a covered in structure.
I hope to make a visit to this plant when it is running, just to see how will the plant runs.
Regards. Andy

[DaBit]

Originally posted by Andy
I hope to make a visit to this plant when it is running, just to see how will the plant runs.
Regards. Andy

Probably fine. I once read an article about the conversion of large R22 heat pumps to propane, done by the German energy company, the RWE. Results were good: capacity dropped a bit, but so did consumed power, resulting in a net increase in COP.

And here in Europe almost all our fridges run on R600a, with succes.