My wife and I are planning on building our retirement home next year in northern Missouri.  The house will have geothermal with radiant floors and forced-air cooling.

We are also planning on building a fishing pond immediately adjacent to where the house will stand.  Said pond will be about 4 or 5 acres with depth near the dam between 30 and 40 feet.  Of course, the pond is a perfect location for a pond loop.

I know that people normally build their pond loops, then sink them in an existing pond.

Now the question:  Since the pond has not yet been built, and since I am going to be moving a heck of a lot of dirt anyway, would it make more sense, while I'm building the pond, to bury the loop under it, rather than sinking the loop after the pond fills up with water?  My thought is that my friends and I (and hopefully one day, grandkids), will be doing a lot of fishing in that pond, and I would just as soon avoid putting a hook through the loop.

I have considered the problem from many angles. 

For instance, how would the thermal performance be 3 feet below the bottom of the pond vs. at the bottom?  Possibly better than at the bottom because I would have 3 feet or so of soil between the loop and the 37 degree water at the bottom of the pond (we're talking heating season).  My thought is that it surely would not matter much,  though, because even the loops that are being sunk today will be silted under in a couple of years, and they apparently continue to perform well for a long time.  My pond will have silting pools in the inflow paths, but silt happens anyway.

On the other hand, without water 'circulating' around the loop, and with a smaller, 'pond-sized' loop, might I create a huge ice block at the bottom of the pond?  Does this happen when regular pond loops get silted in?

Maintenance?  Realistically, fishing out a pond loop to fix it is probably not going to happen.  You would just sink another one, whether the original was sunken or buried.

Cost is not really a consideration, because, like I said, I'll be moving thousands of dollars worth of dirt, anyway.

I talked to a couple of soil engineers at work, and they sniffed around a little bit, and came to the conclusion that although people know almost everything there is to know about pond water temperatures, nobody knew much of anything about the soil temperature immediately under a pond.

Another engineer, who is a construction type, said that when they pour concrete piers underwater, they just assume a constant 55 degrees for calculating curing time of the concrete that's below the bottom of the body of water.  He also told me that thermal conductivity would be very good.

I appreciate you guys reading this long and rambling post.  If anyone has any ideas, I would sure like to hear them.  Mostly I just want to not do something really stupid.

BTW, I love the forum, and have learned a lot from the pro's who hang out here.

Paul

Hi Paul,

Welcome to the forums.

How cold does it get in northern Missouri?

You don't need to worry about ice forming on the loop. Water is densest at 39° F water that is colder than this rises to the top of the pond. This is why ice forms on the top of ponds.

At the very least, I would make the slinkies and put them on the bottom of the pond before filling.

If you bury them, then you don't have a pond loop any more. Then you would have to put a lot more pipe in the ground.


I would set the loops on blocks to keep themfrom getting silted in. You really want the water to be in contact with the pipe.

Good luck and let us know how it all works our

Paul,

Since you are concerned about "putting a hook through the loop", have you considered using a "Slim Jim" heat exchanger in the pond?  Use the internet to read about the Slim Jim heat exchanger.

Hi geodean-thanks for the fast reply.

"How cold does it get in northern Missouri?"
Maybe -20 at the coldest.  Not every winter, but once every 5 winters or so.


"If you bury them, then you don't have a pond loop any more. Then you would have to put a lot more pipe in the ground."
I suspected that might be the case.  However, it seems like it might lie somewhere between a pond loop and a ground loop.  The dirt/clay/whatever at the bottom of the pond would be totally water-soaked, so the thermal coupling between it and the loop would probably be a lot higher than what you achieve in a ground loop (unless the ground loop somehow ends up in the water table). 

That being said, if I wanted to go ahead and bury enough slinky for a ground loop (remember those fish hooks)  :), then it should work fine, right?

"I would set the loops on blocks to keep themfrom getting silted in. You really want the water to be in contact with the pipe."  Those darn fish hooks again...

Anyway, thanks for the reply.  I'll post back in this subject when I reach a decision.

Paul
 

Alton-thanks for the reply.

Actually, I did look at the Slim Jim heat exchangers.  It looked like a lot of money for those stainless steel pancakes.  And here again, who's to say that 5 years from now, somebody won't drag a throw line into one and cause me all kinds of problems?

I guess sometime you just have to take a chance.  I'll probably bury a loop when the time comes, and just see what happens.  When I consider the amount of dirt my buddy will be pushing around with his Cat to build the dam, moving a little more to bury some loop doesn't seem that bad.

And think of it.  A year from now, I'll know something new... 

Paul