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Old 04-13-13, 12:18 PM   #1
dremd
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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 01:24 PM..
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Old 04-13-13, 01:19 PM   #2
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First serious thought on the pump.
Little Giant PE-2.5F-PW Pond Pump 566612, Little Giant Pumps
Looks around 13 foot max lift (only needed to prime) and keeps my 250 gph up to 9 ft lift which seems excessive.

I'd like to do a bit more measuring, to get to 15 foot max head I'd be looking at 150+ watts running current, 80 actually seems a bit much, but I think would be acceptable.

I'm thinking of putting a 5 gallon bucket in the bank perforated with 1/4" (maybe smaller?) drill holes as super corse screen, and some sort of ridgid wire screen inside the 5 gallon bucket to keep most stuff out with the pump screen after that.
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Old 04-13-13, 06:18 PM   #3
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Dremd,

From what I could read in the specs, the units have a coarse SEER rating of 10.5 - 13 ish. This is about what a window AC unit has in terms of BTU cooling/power input.

I bet the efficiency could be WAY increased with little modification with a larger copper exchange coil instead of the keel cooler they use.

The concept of doing direct exchange has been around a long time. This simply means that instead of a long exchange tube, you substitute a shorter, but much more efficient tubing or plate.

A roll of copper tubing, as you suggest would work very well.

Then we need AC to look at it to determine how to better increase the EER. The unit has all the making of efficiency as it has a scroll compressor, co-axial heat exchanger - so it should not be hard.

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Old 04-13-13, 11:06 PM   #4
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Stevehull, where did you find the SEER ratings on those marine units? I never could locate them.

Amazing what being sick can do for project planning, I just saw randens heat exchanger here http://ecorenovator.org/forum/geothe...-pressure.html and thought of a much cheaper heat exchanger than I previously proposed.
PEX on the outside, copper on the inside, use drilled pex plugs soldered to the evaporator line to keep the water side leaks away, and a simple T to feed/ remove bayou water from the heat exchanger. PEX is about 1/4 the price per foot, so I could run a much longer heat exchanger for the same $ if my selection is correct, I could make them for about $2/ ft, so 25-50 feet would not be out of the question. That said, with 1/4" refrigeration tube(my guess on stock size) a 25 ft exchanger would only have 1.6 square feet of exchange surface.
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Old 04-14-13, 02:49 AM   #5
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dremd,
If it were me, I'd start out small to prove the effectiveness. Just spew water out of your pond pump pipe onto the existing evap somewhere it would only sling a little of water in the fan. Maybe up high near the top left corner? You could put in a vertical strip of something waterproof at the edge to block airflow. At a few gallons per minute, the drain hose for your window unit should be able to handle that volume of water. See if you gain any performance over air-only. My guess is that you will. Water conducts and carries heat MUCH better than air.

After preliminary testing, you can decide if you want to do better. The next step could be to add a txv where the capillary tube exists now. Then maybe add water cooling to the line between the condenser discharge and the txv. This way, you would get your existing air cooling plus water subcooling. Grab a small pack of the next tube size up from your existing line and a styrofoam 6-pack chest. Twist the tube up into some shape that will fit in the ice chest with room to run to the splice point, poke a few holes above water level to break out of the chest. Rig up an overflow drain to collect warm water, then figure out how to secure the chest before you cut or braze anything. With only 1/2 ton of heat flow, you would not need a very large exchanger.

Good luck, this stuff is addictive if you have the skill and patience!

jeff
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Old 04-14-13, 10:42 AM   #6
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Dremd,

A quick calculation of the SEER can be had by dividing the btu output by the power in watts input. Not perfect, but a close approximation.

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Old 04-19-13, 11:54 PM   #7
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Quote:
Originally Posted by stevehull View Post
Dremd,

A quick calculation of the SEER can be had by dividing the btu output by the power in watts input. Not perfect, but a close approximation.

Steve
Excellent, I honestly thought that the running watts was sort of a max continuous draw, not a norm draw (Im not very experienced in A/C ratings)
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Old 04-14-13, 04:13 PM   #8
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Dremd,

Another thing to consider doing with the smaller units is using them in "reverse polish" mode. I have found that the heat exchangers in the smaller units can only be pushed so hard before they become the bottleneck in your quest for high efficiency.

The outdoor heat exchangers in these units are designed for massively more airflow and exchange area than the indoor coils. By installing the unit backwards in the window, reversing the connections at the compressor, and adding to the smaller (now outdoor) exchanger to gain heat transfer, you can run the unit at a lower speed to save motor energy while still pumping maximum btu's. This also has the benefit of being able to work on the unit indoors where it's a comfortable temperature. Most window openings are at a height where you can comfortably sit in a chair or barstool to do work and take measurements.

Don't laugh, this works, really! I am using this method to do testing of some suction line heat exchangers now. It really helps your patience factor when you're in a normal environment. No need to worry about rain, snow, wind, heatwave, frostbite, etc.

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Old 04-19-13, 11:57 PM   #9
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Quote:
Originally Posted by jeff5may View Post
Dremd,

Another thing to consider doing with the smaller units is using them in "reverse polish" mode. I have found that the heat exchangers in the smaller units can only be pushed so hard before they become the bottleneck in your quest for high efficiency.

The outdoor heat exchangers in these units are designed for massively more airflow and exchange area than the indoor coils. By installing the unit backwards in the window, reversing the connections at the compressor,
I had such thoughts before, figured I was loosing it, and went on my way, I may not have been. That said, reversed window units are a bit to polish for me.

Thanks for thoughts for sure, and for making me feel a bit less wacko.
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Old 06-28-13, 11:53 AM   #10
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Default Open Loop, Open Loop, Open Loop !

Open loop is way easier, cheaper and THE most efficient way to go. We use 1/2 HP jet pump to feed a Trane water source heat pump (24000 BTU) to heat and cool a 2600 Sq Ft house. Saves us tons o money! Our water temp varies between 46-49 deg F. Reject into a grey water weeping field. In your case back to bayou. Coils in the ground or in the water too costly and innefficient. Keep it open loop man, especially if you have well nearby. Thumperoo

The unitís internal heat exchanging water coil is engineered for maximum heat transfer.The coil is a tube within a tube design.The inner-water tube contains a deep fluted curve to enhance heat transfer and minimize fouling and scaling. It is available in either copper or cupro-nickel (selectable option) coil.The outer refrigerant gas tube is made from steel material.
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