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Old 04-13-13, 11:18 AM   #1
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Default Bayou cooled (open loop) water source air conditioning?

Hey guys, I've been very interested in water source/ ground source cooling (not much heating needed down here, but it would be nice) for quite a while and A/C hacker has had me highly interested for years.

That said the relatively high labor barrier (time) of digging up a yard to bury a loop field has kept me out of the game. However, my camp is located on a small bayou Bayou - Wikipedia, the free encyclopedia that always flows a little, but often a bit and during large rain events a lot, never ever freezes, feels cool year round (sorry no numbers yet), is about 20 feet horizontal and 15 feet vertical from existing window units. A loop field in the bayou is essentially out of the question due to constant dredging, and the crawfish farmers across the bayou dropping their pumps on the bottom.

That leaves me with pumping bayou water to the A/C's and returning it with some of the camps heat. Unfortunately, the water is loaded with mud/ silt/ stuff that I've been afraid would plug up a conventional brazed plate heat exchanger pretty quickly requiring attention that I would like to avoid.

However I know that boats with water cooled A/c's often operate in similar water conditions, so what are they using? Quick google search lead me to these guys (and plenty others very similar) Self Contained Marine Air Conditioning Systems - Prices & Specifications is sure looks to me like approx 3/4 copper (they are using copper nickel for salt water resistance) with 1/4 ish A/c line in side it. The unit on the top of the page is 16,500 btu's and my quick estimation is that it has about a 12 foot long heat exchanger. I would think that it would be pretty difficult to plug up such a heat exchanger as long as I was running an inlet screen and kept the flow rate reasonably high. Any thoughts? I'm not sure how efficiant such a heat exchanger would be, but I can't see any reason not to just make it longer if it didn't exchange enough heat, I wouldn't think that the flow resistance would be dramatically higher than the tubing running to and from the bayou? Any thoughts?

So at the moment I'm thinking about building something similar to what they are selling(for more money than I can spend on such projects) out of an existing window unit.

Proposed steps.
1) remove condenser (or should I leave it so that if pumping fails I still have conventional A/C?)
2 ) if condenser is removed, cut fan off of shaft to reduce load on blower motor, hopefully countering some of the added draw of a pump.
3) build heat exchanger very similar to the marine units, it looks like copper is available in 30 foot coils, and I have 2 units, so I was thinking 15 feet each. More thoughts on this below.
4) Select pump install plumbing. I'm thinking that if I run the return pipe all the way down to bayou level my pump should only have to over come friction losses and counter the thermo siphon that will work against me since I'm heating on the top and cooling on the bottom. More thoughts below.
5) I'm thinking an expansion valve is the way to go here, any thoughts? There is an existing capilary tube, but I have no idea if it would be properly sized for new setup. Any ideas?
6) solder it together, add service ports charge. I'm pretty sure existing units are r-22, which I do have access to a gauge set, I also have a 2 stage vaccume pump(mine) so I just have to come up with a small quantity of r-22 unless I can figure out a good way to recover the existing refrigerant. Any easy ideas?

7) test. Plenty small enough for a kill-a-watt, and since I have 2 identical units, easy to gauge air vs water performance.

I'll have to measure, but I'm guessing 40 feet of plumbingeach direction to and from the bayou. Anybody have a calculator for pump sizing? I'd like to use the same pipe that A/C hacker uses in his field (cost, durability), but connection difficulties may change my mind (only 3-4 connections per A/C all of which are easily accessible so maybe mechanical would be ok?). The marine units want 500 gallons/ hour/ ton, so my 6000 btu's should want 250 ish gallons per hour (or 4 ish gallons per minute) through about 100 feet of tubing and a strainer basket. I'd like a pump that has the ability to make 15 foot head pressure so it could self prime, but I guess that isn't strictly necessary.
Any thoughts highly appreciated.

Although the 16,500 btu unit uses a shorter heat exchanger coil than I am considering AND I'm only 6,000 btu per unit, I'm not seeing virtually any efficacy information on the marine units, I realize it is hard to provide due to changing water temperatures, but I AM defiantly after some improvement in efficacy and the extra copper cost isn't all that much in the total cost. Any thoughts highly appreciated here. Anybody ever use / find info on such a heat exchanger?

Last edited by dremd; 04-13-13 at 12:24 PM..
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