geothermal pond loop?

[Gale Hawkins]

We use the two well open loop so we have a 60 degree source year round. Before we bought they were getting water from next door well then we bought that place right after we dug our own well so we did not have to do any exterior plumbing.

Not sure if pumping energy costs are about the same for each system or not. Our acid water ate both of our heat pump exchangers after 15 years and they were heavy in nickel from the get go so we are going to have to replace but I think every 15-20 years the technology has improved so it has its up side too.

If I lived in a flat area and did not have the wells I would go horizonal perhaps. We just live in a area where billions of gallons of water if flowing out of the ground due to rising water table. Many wells have had to add risers to keep water from flowing into the yards year round.

 

[spc]

I have a closed loop in my pond. Its been 6 years and is working fine. The pond is 2/3 of an acre and the loop is down about 15 feet. My brother lives on the other side of the pond and he runs his geo off his well water. He dumps the water into the pond. His system also is working fine. My system cost a little more upfront but i wasnt crazy about pumping all that water out of the aquifier.

 

[pat32rf]

We installed a 3 Ton closed pond loop system a few years back. Our pond is actually a small lake but the shallow muddy end is closest to the house. As a result the contractor used a 1000' loop, but ran it towards the deep section, instead of slinky coils. The far end of the loop is in 20' of water but we had to cross 300' of 3-5' muddy shallows to get there. In spots that mud is over 6' deep so the piping just sank down into it.
Right now the ice is about 14" thick, outside temp is minus 20C and the geothermal doesn't really run long enough to preheat the water above 90F. When I have a fire going in the fireplace insert the house temp will rise about 6deg F above the thermostat set point so the geo compressor might not run all day. On those days I just keep the furnace fan going....

Due to acidic water our contractor advised against an open loop and when I asked about the DX systems he explained that he had installed few 15 years ago but ALL had developed leaks in the buried copper coils, (again due to the acidic soils).
I also looked into the plate heat exchangers but we didn't have enough water depth. Similarly out bedrock is too close to the surface for a horizontal loop.

I have a friend (?) who used a compressor/heat exchange unit from a hi-rise office building and just pumped his well water thru it (instead of the water from a hi=rise cooling tower system). Cost him about $5000 to buy, was a DIY project and he's been happy for ten years. Discharges into his goldfish pond via self draining elevated pipe.
(ours cost $22,000, including ductwork)

 

[Chilly807]

We did 3 horizontal slinkys for our 3 ton unit.

Ours is much the same, closed loop with 3 100 foot trenches 6 feet deep and 6 feet wide. 1000 feet of pipe in each trench.

Sean

 

[pat32rf]

3000' of pipe in a trench versus 1000' in a pond for a three ton unit. Now I see why he wanted to use a pond loop. We just tye-wrapped 20ft lengths of 3/8 rebar to our pipe, towed it out and let it sink when he charged it with antifreeze.

 

[20 20]

Thanks for the info I'm still in the thought process. I figure I'm getting older and as much as I like heating with wood, time will more then likely force me to another style of heat{and on the plus side cool also}. Our pond is right at our back door and as of now is 8-10' deep{plan on dredging more}.

 

[Chilly807]

Thanks for the info I'm still in the thought process. I figure I'm getting older and as much as I like heating with wood, time will more then likely force me to another style of heat{and on the plus side cool also}. Our pond is right at our back door and as of now is 8-10' deep{plan on dredging more}.

Our material costs were about $1500 CDN for all the external piping including couplers, etc. The excavation cost was $1200 for a day of digging and backfilling.

I'd sooner have the loops buried underground from a damage point of view. The heat pump puts out a considerable amount of chilled water, which may contribute to the pond freezing. Mine has an antifreeze mixture in the external loop, and the temperature I was reading in the ground loop "tower" on Friday last week was 2.2 degrees C. Close to freezing.

If you're going to use an open loop, you should be sure you have a clean, relatively soft water source. If not you're looking for problems with the heat exchangers over time. A closed loop using hard water at least will not have a fresh source of calcium, etc to clog the works up.

Sean

 

[20 20]

Chilly807; After all the advice{thanks everyone} if I do end up going geothermal it will be closed loop, our ground water in this area is very hard.
If I go with the pond I may dredge the depth of the pond and then dig down even more{couple extra feet, while I'm allready there} place the pipe and bury it in a thin layer of sand? That way the line would be protected and I'd be more then far enough down, just not sure if it be a good idea?

 

[Chilly807]

The only concern I'd have with that is the length of pipe would be sized for water immersion, and it would be at least partly in the sand. The only water immersion one I've seen was in a lake, and they actually built a cage of PVC pipe and used that as a frame for the piping. I don't know how much difference there would be, probably the rate of heat transfer would be somewhere in the middle between the two mediums?

I was told that the best conduction, aside from water, was wet clay soil due to the improved surface contact with the pipe. Sandy or gravelly soil was the worst conductor.

Sean

 

[Rob-D]

Hi Gang,
Thanks for all the good input! I have a 12 foot deep pond about 1/3 to 1/2 acre that I can use but I can also dig a trench with my 48 BH and run a slinky in it.
When I built the house back in '92 I put radiant heat in with 50% antifreeze so I think geo should be a good choice for us.
Rob