I am considering having a GHP installed on my property in Western NY. The contractors that I have talked to would like to use a horizontal closed loop design with a 4 ton unit. I have plenty of space to run the loops, but the contractor mentioned using a small pond for part of the loop. The pond if about 35' in diameter and 12 feet at its deepest. It is spring fed with an input of 6-30 gallons per minute depending on if there is run off or not. In five years it has never been below 6 gpm input. Does anyone think that this is big enough to support a 4 ton unit? The pond is 200 feet away from the house. I could go hybrid and use multiple loops along with the pond as well. Out of curiosity, has anyone used the slim jim plate heat exchangers. How about one made out of copper for use in a pond?

A mix of ground loops (you need to get to the pond anyway) plus a slim jim near the spring makes sense.

You have to be careful with the pressure drop if you are 200ft away. Also, would need to balance the flow if you go hybrid with a slim jim. I am not sure if it is worth the extra cost of a slim jim. Actually, HDPE slinkies work great in ponds in Western New York.

You need to excavate a 200ft trench anyway. I would run a header trench to the pond, and the last 100-150ft I would run it deeper to come back with 2 slinkies in the same trench, one at 8ft and one at 5 ft. The other 2 or 3 circuits I would sink in the pond. If you have 6 gpm flow through the pond, and fed by 50+ degree water, it should work fine. Make sure you slightly oversize he heat exchanger if you are away from the great lakes, the climate and the load on the loop varies greatly depending on your location in western new york.

http://www.ripoffreport.com/heating-cooling-ventilation/aweb-supply-alan-wat/aweb-supply-alan-watts-sli-2q8c4.htm

Did this ever get resolved?

Low flow is probably correct - I don't think there is anything wrong technically with slim jims.

You would have to figure out if the advantage of staying right near the 50F+ coming from the spring outweighs the cost advantage of HDPE (which will be spread out more and would thus see lower temps in winter - maybe 40F?).

I think given the limited area the slim jims have for heat exchange, they are very sensitive to have water flowing around them. Thus I think that HDPE is much more predictable in their performance, even in such a small pond. I would increase the size slightly, go with 400ft instead of 300ft of slinky per ton, so you have a comfortable margin.

Just out of curiosity, why doesn't anyone use coiled copper pipe in a pond loop? It is used in DX systems, so why not in ponds? cost, reliability or has there just been no need...

Posted By aforgnone on 20 Dec 2011 06:00 PM
cost, reliability or has there just been no need...

All of the above...

IMO, cost.

To make most efficient use of copper's extremely high thermal conductivity would require water outside tubing to be moving. Why spring for very pricey copper only to have the limiting factor for heat exchange become the slow natural convection of water in close proximity to the copper? This illustrates why most pond loops consist of cheaper longer coils of plastic pipe.

I agree with docjenser. Doing a hybrid system sounds great if designed properly..I am working on one right now and playing with the design as the homeowner wants the trenches dug in different directions, so the loops keep moving.

Where in Western, NY are you located?

Anyone who has priced a SlimJim will not be smitten. Price per ton is for southen applications- for northern work they suggest significantly more plates running cost even higher. Recent job required 15K in slim jims or 2K in HDPE, guess which we picked.