Sort of OT: air conditioning redux- boosting efficiency

I have a pair of Sanyo split system air conditioners, Persently defunct due to leaks in the evaporator. I have read that once the leaks start,
they will develop in multiple places, so a solder repair is a maybe thing over time.
The local water table is perhaps 15 feet down from the surface, giving me an inexpensive source of ~55 degree F water.
I am considering an experiment with one of the systems, repairing the leaks, sucking it down and charging it again, with an added coil of copper in the return line.
The coil would be placed in a bucket of the cold well water.
This would put the additional cooling before the compressor, not the ideal place, but easy to do.
It would cost the Freon and (paid) labor to put it in. The systems are pretty much history anyway so I am not afraid of burning them up.
Has anyone tried this? Any thoughts?
Kevin Gallimore
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Yes. This is called a ground-loop heat pump in practice, using many yards of tubing underground for large thermal mass. You see the thermal mass of a bucket of cold well water is pretty low, and pumping water costs $$$.
Doug
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snipped-for-privacy@aol.com wrote:

I am aware of commercial geothermal pumps. This would be an attempt to kluge an air cooled A/C unit. The water in the bucket (lets call it the outer shell of a heat exchanger) would be continually replaced by fresh water. The overflow would water the lawn. I suppose the way to figure this is to estimate the heat transfer of a length of tubing, and knowing the temperature differential, calculate the BTU/HR transfer. One of the questions I have is what difference cooling the returning gas (before the compressor)or cooling the compressed fluid (after the compressor)will make.
Kevin Gallimore
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wrote:

I've done a lot of experiments along these lines over the years. My current setup is the best that I've found short of a full blown ground source heat pump (which is to expensive to install compared to the payback).
My first system was a old 5 ton very inefficient condenser with all the components used and kludged together. I started with a coil of copper coming directly out of the compressor into a 1/3 cut off 55 gallon barrel vat. The water in that tank would get very hot. I tried pumping it through a series of troughs above the tank and back but my "water tower" wasn't big enough to work well. After leaving this tank it went to the original too small condenser coils in the original unit (I figure the unit was originally about 5 SEER rating). After leaving the air coils it then went to a old heavy duty commercial condenser coil which was all copper. I had this sitting inside the other 2/3's of the 55 gallon barrel. This barrel I cooled with two 16" x 20' roofing panels like my shop is built from as troughs. The top one had the water pumping into it which then flowed to the other end and then back via the bottom trough. This worked ok but was a pain to keep clean.
Overall this system worked well and based on measurements I figure that I took the original 5 SEER unit up to about a 10-12 SEER unit with my improvements. But it was with a cost. I had to maintain the system and powering the water pumps for cooling the water decreased efficiency.
The next year I got rid of everything except the original air coils and the after cooling coils. I placed the old commercial condenser coil into a 8' stock tank which I purchased. This worked much better without the cost of pumping water and keeping the troughs clean. It also made a heated swimming pool for my daughter who loved the 90-100 deg water temp it usually maintained. Of course there was the usual problem of keeping a pools water clean and sanitary but that would of been the case whether the coil was in there or not.
After a summer where we got a $240 electric bill and then seeing the electric rate increase from $0.08/kwhr to $0.11/kwhr that winter I decided I had to do better for the next cooling season. All stops where pulled and I did a lot of research. I came very close to getting a evaporative cooled condenser unit made in El Paso. This area is border line on evaporative cooling but it works ok most of the time. In fact the above system was put in place because of the some times humid days which made the evaporative coolers useless and caused a 90 deg with 95% humidity in the house during some of the hottest days of summer. Due to other money considerations I was forced to forget about the evaporative cooled compressor. However I did managed to get a old RUUD condenser unit which was state of the art high efficiency heat pump in its day. It has two sets of condenser coils on each side of the compressor instead of the one which the standard units had. It was rated at 4 tons but doing research on the part number to replace the compressor (which was supposed to be out and the reason the unit had been replaced) I found that they had installed a 3 ton piston compressor with the double coils to make the high efficiency unit. I replaced this compressor with a 3 ton scroll compressor and then found that the "H" valve used to switch from heating to cooling mode was out (the real probable cause of the unit being replaced). After replacing this valve with another from another old unit (I have scrounging rights to a HVAC scrap pile making this type work easy) I found it worked very well.
I kept the after cooling condenser coil in the tank but found it didn't work anywhere near as hard as with the original unit. During this install I also installed a set of solenoid valves and thermostat which served to switch the water cooled coil in only when the air temperature was above 85 deg. This allowed the tank water to cool at night when it wasn't needed (also preventing the water from adding heat to the refrigerant during that time).
Inside the house I installed a new 80% efficient gas heater and I used a brand new high efficiency 5 ton evaporator coil above it.
Measurements during the summer that was installed showed a temperature drop across the coil of 20-30 deg with airflow of 1600 cfm. The condenser is drawing about 13-14 amps during this (which includes the two condenser fans). Based on this and other figures I figure the unit is in the 14-16 SEER efficiency area possibly a little higher. This is the best that I've seen short of a full blown ground source unit which would cost well over $10,000 to install. My cost not including labor(which was my own) for the system was less than $1500. Which is less than the evaporative cooled condenser unit I was considering cost.
I've been extremely happy with the performance of this unit. I did have to replace the old commercial condenser coil last year since it developed a leak. Currently I just have a 50' coil of copper tubing in its place. It's not as efficient but with this unit that's not as much of a problem. I also traded the 8' tank for a smaller oval tank. My dad needed a big tank for one of his places and my daughter is old enough that the 8' tank wasn't really big enough to swim in. The smaller oval tank seems to be sufficient with the double sized condenser coils on the unit.
I guess to sum it up what I'd recommend in your case is to replace the evaporator with a new high efficiency coil, put your extra cooling on the high side line between the compressor and the evaporator, and enjoy it. I think you might be surprised at how well it works but keep in mind any cost of pumping the water.
Wayne Cook Shamrock, TX http://members.dslextreme.com/users/waynecook
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Wayne Cook wrote:

(snip a lot of good stuff)
That's just what I was interested in hearing. the only operational problem is that I can't buy Freon (legally). Even when I include the retail cost of Freon and someone's time to suck down the system and pour it in, it may be worth it. It will be an interesting experiment. Around here, the groundwater depth would make it practical (there's a lot of salt water too). I think of it as a keel cooler for the A/C.
Thanks,
Kevin Gallimore
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wrote:

Hope it works well for you.

You're welcome. Wayne Cook Shamrock, TX http://members.dslextreme.com/users/waynecook
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wrote:

So, go get your own refrigerant technician license and you can go buy your own, legally. Open a cash customer account at your local refrigeration supply house <cough_www.JohnstoneSupply.com_cough> and they'll be glad to sell you everything you need, tell you where to take the test, and even steer you toward continuing education classes and specialized technical help. Or to another of their local customer companies that have done it before.
The test isn't difficult (multiple choice AKA multiple guess), but with the license also comes the responsibility - do something stupid like venting refrigerant and get caught, and you can't plead ignorance as an excuse. If they decide you're going to be "Example Boy" they can spank you hard, and no liability insurance allowed - cash only.
The expensive part is buying any service equipment you can't get used or scrounge - new vacuum pumps are ~$300, recovery machines are ~$600, leak detectors and charging manifolds start at $100 each...
Oh, and you don't "pour it in", you pump or siphon it in, even if you are using R-11 (or a replacement for it) which is still a liquid at room temperature and sea level atmospheric pressure. The big 50-ton-plus centrifugal chillers work under a partial vacuum, they have more trouble purging the air that leaks in than the refrigerant leaking out. (Or at least that's how you answer it on the test. I've never played with one myself - but I'm licensed to if I want to.)

If you are very close to the ocean, salt - or brackish - groundwater is a bad thing. Depending on the exact composition, it can be hell on the water cooled condensing coil materials. And pumping out a lot of brackish water is worse, because that depletes the water table and encourages more salt water to infiltrate from the ocean. And your local water agency will have a cow, they avoid doing anything that makes the situation worse.
If your ground water is brackish, I'd use a cooling tower and run domestic fresh drinking water in the loop. Even after replacing the evaporated water you still come out ahead just from the extra efficiency of the refrigerant-to-water heat transfer.
--<< Bruce >>--
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
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Bruce L. Bergman wrote:

This is most assuredly true. It becomes a bang/buck question for something I might do once a decade.
do something stupid

Again, most assuredly true. I do not see the sense of it, however. The two systems in the house just vented about ten pounds of Freon to the atmosphere. The most common failure mode in air conditioning systems is losing refrigerant. The problem of venting a couple of ounces to purge lines would seem to be down in the noise.

Having put the original systems in 14 years ago, I still have the vacuum pump, halogen leak detector and manifold. Recovery machines were not generally used for home systems at the time.

A poor choice of words on my part. Like "suck it down".

That it can, although the problem here is iron.
And pumping out a lot of

Down 15 feet or so is considered "surface water" (around here this is fresh water with a high iron content). The town requires a permit to put in the pump, but unless I pump more than 10,000 gallons a day, the state DEP is not involved. (Surface)well water is commonly used around here to water lawns and gardens. Most of the houses in this part of town have a well for this purpose.

If the experiment indicated a significant improvement, I would probably change over to a closed loop (with a DI water/ethyl alcohol mix) with one end down in the well, and the other in a heat exchanger on the surface. I'm too lazy to deal with winterizing a cooling tower in a place where we often have freezing temeratures and a need for air conditioning in the same week.
Thanks for the cautions. I plan to have an aquaintance from work (who did get the licence and does jobs on the side) evacuate and re-charge the system in question. Due to a strange brain defect that I have noticed in others here, it _really_ bothers me when I can't do something myself.
Kevin Gallimore
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