Question re: Closed Pond Loop Cooling

MetalManglerJune 15, 2005

I'm contemplating trying to cool my house with a closed pond loop system. I had been thinking that all I'd do is circulate the fluid in the system and blow air over a radiator into my existing duct work. Is this correct? I'm looking to do this as inexpensive as possible and as much DIY as possible. At this point my system (as planned) would be about 130 ft of copper tubing in the pond, some plastic piping to get it between the house and the pond, some sort of fluid pump to circulate the coolant (water or some other medium) and an uncased evaporator coil in my furnace. Total cost should be under $500. Am I missing something?


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Don't have the thermal background to say if 130 ft will suffice to "cool" unspecified area, or by how many degrees etc. Suggest you think about using copper in the pond, believe that acidic water will slowly eat it away. I'd suggest plastic the whole way . . . pretty cheap though it does not have as good heat transfer qualities of copper. BUT . . it's seamless and VERY rugged / long-lived. Make up for the lack of thermal qualities by way of slow circulation. That will help your heat exchanger efficiency in the house as well.

Depending upon size / temp of pond, and size of area you wish to cool; COULD warm the pond up to the point where it can no longer supply much cooling; and if you do so it may well change what's in the pond too by virtue of higher temps. Your basic principle seems quite sane; I did a similar thing once using incoming water line . . only worked when water was RUNNING, or you had to leave something on to keep the cooling going. This will cool the air, but only dehumidify it a bit; not a lot as conventional A/C. Good luck, and post back with results . . .


    Bookmark   June 15, 2005 at 6:17AM
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I based my length of copper on a desire to match a 3 ton AC system (36,000 BTU/hr) with the copper water to water coefficient of heat transfer (60 - 80 on the chart, so I used 70) and a 30 degree heat difference. That heat differential was based on the fact that my pond is spring fed (I'm using a rough calc of 55 degrees) and I'm planning on using the system when the weather gets about 85 degrees.

All those numbers told me that I would need about 17 sq ft of copper. When I did the calculations for 1/2" copper tubing it came out to about 130 feet of copper tubing will have a surface area of about 17 sq ft. I think I did the math right, but I could very easily have slipped a decimal point. :-)

The idea of using plastic is possible, but I'm concerned that I would need significantly more to get the same cooling. Your mention of slowing the water flow to allow longer time to equalize the temperature is an idea, however I haven't seen any information about how to calculate that.

BTW: I'm in Eastern NY near the Massachusettes border, and I used a 3 ton AC system as my goal based on pure SWAG (Scientific Wild A** Guess). I have a 2 story 2500 sq ft house. A 36,000 BTU system appears to be common, although i understand that due to insulation, windows, wall space, etc, etc etc. I may be over/under sizing the system.

It looks like if I go with a commercial evaporator coil I could go with a 5 ton coil for about $100 more than the 3 ton, so I might do that just in case I wish to beef up the system if I'm undersized. And of course, just adding more copper in the pond. :-)


    Bookmark   June 15, 2005 at 6:50AM
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may i suggest slitting yoru coil in two ro three and placing them farther apart along the bottom of your pond so you are drawing cool water from a larger area.....i know they do this with geothermal heat pumps...and to heat an "average" home they suggest about 4 acres of water 6 feet deep...but that is for the heating end of it..i would think cooling would be much less.....i have a friend who uses a deisle truck rad with a fan behind it a nd runs an old well through it and jsut dumps the water down his well but i think it wastes a lot of water.....your idea i think will work...but it wont help take any moisture out fo the you cool the house you will need another source of dehumidifier

    Bookmark   June 21, 2005 at 10:57PM
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