Next week we are putting the heat exchanger for my new HVAC geo-thermal system into the lake. Rather than loops of tubing, we are using stainless steel plate radiator (https://awebgeo.com/). It's going in about 13.5' feet of water. Generally they claim you need about a 1/4 acre pond with 10' of depth to support one of these, so it should have zero impact in a 50 acre lake, especially with the amount of flow through water exchange we have.

It seems like to me that would make a lot of sense, but for some reason they have completely quit installing them in this area, back in the day I have dug in the lines from the pond to the house for the HVAC companies that were installing them but not for 20 yrs. something about the coils of pipe, (that's what they used back then) freezing up or something.
I am wanting to build a retirement house, cabin, by my lake, 15A, here in the near future,and was really trying to figure out how to utilize that option. I may have more questions. Good Luck!

The installer I am using has done a bunch in this area. If the coils are freezing then they aren't sizing it correctly. I'm using a Waterfurnace system, not cheap but with my electric bills this summer it should pay for itself.

The engineering sounds awesome!

Those stainless steel plate radiators do look very expensive, unless the manufacturer volume is up to some serious economies of scale.

We have gotten a few quotes over the years, all too expensive to ever pay back. We don't have air vents upstairs, so we are going to go mini splits instead. I was told there are a few problems with heat exchangers in ponds:

1. Vinyl tubing will float up if air gets in the lines when you purge. Need to throw something over the top like chain link fence to keep it down and that is expensive.
2. Radiator-style heat exchangers get life and muck on them. If you have zebra mussels, they will clog it all up. You need to clean them often for best performance.
3. In our northern climes, they will get a pretty thick layer of ice on them depending on the weather. It takes a long time for the ice to melt when it is in the pond bottom. Enough ice will get it to float and potentially break lines when it merges with the surface ice and blows around.

They recommend trenches and wells instead.

In my case, the coil and trench length needed is about 30ft shy of reaching the pond. There is no point to go into the water.

If you can place the exchanger near flowing water, you may have better luck with freeze issues, or a massive area for heat exchange. Oversize it a fair bit.

Can't wait to see pictures of your project...!!!

Does it stand on legs to elevate it above the bottom of the pond?

I had considered doing this when I replaced the two units at the farm but my pond has suspended sediment and algae that would clog the radiator.

I put a mini-split in my shop. I love it. Very efficient.

The plate is mounted in an A frame that holds it upright and off the bottom.

We went geothermal on a house remodel about 12 years ago. Wells were recommended to me at the time as being more failsafe and efficient. I dont know if that is still accurate. Don't know cost comparisons either.

Think they drilled 4 pretty deep holes in my backyard, put in pipe and connected them somehow. Wish I had taken measurements and pictures before they covered it up and seeded the grass.

I was going to put a geothermal system at our cabin. We have a large lake. Thought of putting the pipe coils in lake. Then changed to a pit idea. Dig large hole ( 10 feet deep) in bottom of the lake, then put intake pipe in hole so you would bring in lake water to system, cover with gravel to filter water. This would be just like a water well. The cold or hot water would then be put back in the lake at another spot to not affect the temp of incoming water. Then would also put an extra air hose in hole that would have lots of holes in it, so you could pump a lot of air through ( 100 cfm or more ) to clean the gravel of sediment when it would need cleaning. Was sure this would of worked but lake filled before we got to putting in. We have a lot of clay in our ground, do not need to worry about pond liner.
This was just my idea not a proven system so not to buy a lot of pipe or a radiator system that could be caught with fishing hooks. But could be changed over if it would have not worked. Also remember everything would need to be below the frost line.

Our geothermal system was installed in 2009 - coils on the bottom in 10-12 feet of water. It has been operating continuously since. Our system was filled with soft water at installation. Other than cleaning the air filter and an annual check up it just keeps on going.

This is the plate heat exchanger for the system getting ready to go in the lake. It is mounted in an A frame and the 2nd picture shows the pipes being attached. It was dropped in 15 feet of water. I suited up and dove (SCUBA) to check the placement and set concrete blocks on the feet. The plate weighed 400# dry, so it's not going anywhere.

I realize this is an old topic, but installing a geothermal HVAC system sounds very interesting, and I wanted to share my opinion. It's nice to see that you are also considering the environmental impact. I also like your out-of-the-box thinking and use of alternatives to traditional pipes. It seems that with this knowledge, you could become a good plumber and make good money, as plumbers are in high demand, and you can see for yourself at https://www.howtobecomeaplumber.org/are-plumbers-in-demand/. Good luck with the installation, and your new system brings you energy efficiency and cost savings.