refrigerant efficiency

After only 30 years it looks like one of my apple cooler's compressor and evaporator unit needs to be replaced. It uses 502 refrigerant. This was the best choice for low temperature coolers with electric defrost when I got it new.
Not many 502 systems are installed today because 502 is so hard to get. (Its very similar to the now banned R12) But I own a 30 lb. jug plus about a 10 lb. charge in the old system.
A fella told me the 502 systems are inherently more efficient because they run at lower operating pressure. Efficiency is important, the electric is north of $1K per month when it runs.
I'm searching all the commercial cooler units catalogs and I'm finding nothing on efficiency. Most compressor/evaporators can be set up for more than one refrigerant.
So, what's best?
Karl

Karl Townsend wrote:
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It is a lot more complicated than that. Operating pressure has nothing to do with efficiency. R502 is a mixture of two different gases, see <http://www.free-ed.net/sweethaven/MechTech/Refrigeration/coursemain.asp?lesNum=4&modNum=1 for more info.
Efficiency has to do with how much work it takes to condense the gas, compared to how much heat that vaporizing gas absorbs. The numbers are different for every gas. Of course, you want the condenser to operate at the lowest possible pressure and temperature to make the load on the compressor lower. That's why a lot of commercial refrigeration units use water-cooled condensers and evaporative cooling towers.
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I have a Fortran program that evaluates performance given some numbers on the compressor, evap and condenser temperatures, etc. Unfortunately, I haven't converted this program to run on my Linux system, but it might be able to be converted by f772c. It has data for R502, as well as a number of other refrigerants common many years ago. I did some simulation with the program and found Propane was the best refrigerant for comfort cooling (air conditioning). It produced the same cooling at something like 20% less energy input to the compressor.
At 1 K $ /month, maybe you need to look at some alternative energy schemes, like solar-powered cooling. You can heat a heat transfer fluid with solar collectors and use that to run an absorption chiller. That might only be the first stage of a cascade chiller, but it would handle the majority of the work. An absorption chiller can easily deliver 40 F water. If you tweak the parameters, you can get Lithium Bromide to produce much colder temperatures with lower heat load.
Jon

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    Is this a commercial Fortran program, or one of your own programming?
    Note that linux systems usually use gcc (Gnu C Compiler), and the more recent versions can bet tweaked to also produce a Fortran 77 compiler (g77).
    Also, the lastest "Studio11" and Studio12" compiler suites (now free) from Sun include f77, f90, and f95, FWIW.
    Is there somewhere where I can pick up this program? I would be interested in playing with it. (Note -- you probably *can't* simply e-mail me the source, because my system is set up to totally block *any* e-mail larger than 30K total size -- before I ever get a chance to see who it is from. This keeps all the virus e-mail out of my mailboxes and mailing lists.
    An anonymous FTP site -- or a web site would work, since that could bypass the e-mail blocking.
    Thanks,         DoN.

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Doesn't a lower operating pressure imply that less work is done to condense the gas?
It IS much more complicated than that, but operating pressure is relevant.

On Tue, 28 Aug 2007 19:29:28 -0500, "Karl Townsend"
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Before you start, did you call the local power co-op and work on that problem of getting 3-phase out to the farm? This is another motor that can be changed over, besides the water well. The added efficiency means it costs less to run a compressor on 3-phase than single-phase, and every little bit helps.
As to refrigerant selection, that's way above my pay grade (haven't done it for money in a while). The chart says R-404a is the long term choice to replace R-502 for low temp applications. But confirm this with the equipment makers, they have it all figured out. Unless you have a local service company that stocks all the esoteric refrigerants needed to service walk-in refrigeration, you need to keep a stock of refrigerant, a few spare filter-driers and other parts and the right gauge manifold on site - especially handy if you call for service and find out Fred's taking a week off to go fishing, and you have to figure it out yourself...
--<< Bruce >>--

On Tue, 28 Aug 2007 19:29:28 -0500, "Karl Townsend"
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This was ~25 years ago, but all the big storage's around this area were using ammonia. I remember one of them had a three phase 150hp motor driving the compressor. It wasn't uncommon back then to find a four wheel trailer with an ammonia tank on it wheeled right into the compressor area and hooked on. At least until they figured out where the leak was and didn't have to keep adding more to it :)
Only the small systems used freon back then and weren't very common.

wrote:
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I've several old engineering manuals that put ammonia gas as #1 for overall efficiency. Nasty stuff, but still used for large warehouse and ice-making operations. Also biodegradeable and ozone-friendly. You probably won't find the information you need out of a catalog, efficiency depends on a lot of things, one reason the books are so thick...
Stan

On Thu, 30 Aug 2007 20:23:22 -0700, snipped-for-privacy@prolynx.com wrote:
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But have you ever been near a leaking SO2 system? Gerry :-)} London, Canada

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Ayupp! When I was 13, I made a "Globe Refrigerator" from copper, SO2, and silica gel.
You heated the "condensor" (absorber) in a fire while cooling the evaporator in a bucket of water.
Then you placed the evap in the ice chest/cooler/cabinet, and put the absorber in a bucket of cool water, and let the SO2 slowly boil out of the evap.
It would cool for five or six hours on a "charge".
SEVERAL leaks manifest themselves during the first cycle of assembly, charging, uncharging, and leak-fixing. <G>
LLoyd

Gerald Miller wrote:
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Back when I was in grade school (1940s) a family had one (household refrigerator using amonia) leak, fortunately only the pet (forget what kind of pet) was home. Did it in. Nasty stuff to breathe. ...lew...

Lew Hartswick wrote:
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Woops Maybe that was S O 2 Now that I think about it again. ...lew...

On Fri, 31 Aug 2007 08:32:35 -0600, Lew Hartswick
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The reefer here in my RV was ammonia charged. Blew a fitting about a year ago (which is why its now my dry storage).
Prior to that..Id had an ant problem here in the RV park.
Havent seen an ant, spider, moth, roach or any other critter since then inside the RV.
Nasty!
Gunner

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Most of the RV fridges are absorption types, can use propane or electric heaters to do the boiling. Active stuff is ammonia gas, water and a little hydrogen. Uses heat of solution rather than heat of vaporization. Not as efficient and doesn't work at as high a pressure as compressor-type ammonia systems. Also needs to be held level to work. But well-suited for the purpose, no electric current needed and it's quiet.
Stan

I didn't get the original message but Karl, you can use R-408 as a drop in replacment for R-502. The tech manuals will not agree but We have done it many times, sometimes on a unit with a hermeticly sealed compressor where there was not an easy way to change the oil. On an apple box I suspect you have semi-hermetic compressors. The efficiency will be very close to original with only slightly higher head pressures. Keep those condensers clean! If you equipment is shot maybe it is time to upgrade. But if the system has lost it's charge then use the R-408. I recommend if the system is very short, remove the refrigerant change oil to alkybenzine (avoid poe if possible it cleans the system and cloggs strainers) change filter, evacuate and charge with R-408. If system is only slightly short of refrigerant top it off . BTW R-502 is closer to the very popular R-404 today's choice than R-12 in terms of pressures. Good Luck Lyndell
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