pond loop or horizontal slinky loop

[Fordguy64]

So in the spring we are going to have a half acre 12ft deep pond dug. Im going to go ahead and install some ground loops while the yard is a mess. I live in Cincinnati oh. Ive come up with a 3 ton system. My findings are that i will need a minimum of 600' 3/4 pipe per ton for horizontal slinky loop. Ive found that for a pond loop ill need roughly 350ft of 3/4 pipe per ton.

two problems i see with the pond are

first one being that this will be a fishing/ swimming pond. I really dont want my line getting caught on the loops in the pond and neither will my wife..

second issue is winter time temps. i know the bottom of the pond should only get down to 39* but i feel like the "55*" water from the horizontal slinky loop will be much better for heating season. Heating season will be our main usage for this system.


just curious what your thoughts are?

[jeff5may]

If heating is your main concern, the ground would be a better choice for the figures you quote. With the loop in the bottom of the pond, it will be exposed to the heaviest water in the pond. As you already stated, this water will always bottom out at 39 degF. Not great for performance. The experts state the 350' per ton is good only for cooling duty with a well exposed loop, flowing water or convection flow. For a stagnant fluid bed and heating duty, they recommend 400 to 500. If you were doing lots of cooling with the system, the pond would be a better fit.

Regarding the slinky loop, the longer and deeper the loop is, the better. Since the pipe is coiled, it isn't quite as effective as straight runs. Minimal oversizing pays off big time. The deeper the loop is laid in the ground, the less seasonal temperature swinging it will experience.

[oil pan 4]

Do both.
Since you are having the pond dug put the loops under about 6 inches of dirt at the bottom of the pond.

[Fordguy64]

That’s an interesting idea oil pan.. but I feel like that will still yeild lower loop temperatures in the winter

[jeff5may]

It all depends on various things to do with details. Assuming you bury the slinky loop deep and oversize it, the leaving water temp should come out close to 50 (at first) after the rig has run for a few days or weeks. So your evaporator temperature will end up below 40. With the slinky drawing constantly from the buried field, the temperature will droop below 40 after the low hanging fruit (local heat) has been plucked. This local droop below 55 may or may not recharge a whole lot if you're not also cooling your zones with the same field.

With the slinky loop below the pond, the same thing ain't gonna happen. From day one, you will always have around 40 degree or higher ground temperature loop water that won't droop below freezing. Plus, if the sloppy mud bottom field loop fluid gets below freezing, the stagnant water will try to float, and if it can, it will. However, the submerged slinky loop will outperform a dry buried loop of the same length. So it would be a bit more delta T than the dry loop at first, but perform better the more you use it.

[Fordguy64]

Jeff thanks for explaining that. that makes perfect sense.. what are the thoughts on the depth of the loop field below the pond? 12"? more? less?

[oil pan 4]

The trick is for the pond and ground, you can run them parallel and just shut off the pond loop in the winter.
That pond loop will be pretty nice in the summer for A/C.

[Fordguy64]

I wonder if I just ran the loops out in straight runs around the bottom of the pond..

Pumping the water will be something I need to keep an eye on. Trying to keep the head pressure down is tough

Basically I’m thinking 4 loops of 600. The waters edge of the pond is about 130 feet from the corner of the house the the loops will come out of. I’d like to run all the loops into the house to a manifold. That way I can put flow meters on them and make sure they all get the right flow. I would run all 8 pipes Down one trench 3 feet wide and 6 feet deep keeping pipe spacing as far as possible from each other while staying under 4 feet from the surface. That will eat up about 260 of the 600 feet of pipe. Then the other 340 feet of pipe will be layed out in the bottom of the pond or just under the bottom surface of the pond. That should give me a hybrid pond/horizontal loop field?

[oil pan 4]

That sounds good, then attach thermometer to the loops to see if there is a big difference.
You my be correct and find then pond loops too cold in the winter, so just turn them off.
You may even want to try putting valving that will make ground and pond loops work in serries. You could put most of the the summer air conditioning heat under ground to save for later, them further cool the loop water by going under the pond.

[jeff5may]

Just grab some free ground loop design software from the web and have at it. I know that climate master and water furnace both had free stuff available a few years ago. The ones that you have to pay for are more extensive and robust, but for a single family home size system, you don't need the extra abilities.

With 4 parallel loops, you shouldn't have any head pressure woes. The more important factor to consider is velocity. The fluid has to be travelling a certain speed to get turbulence and the resulting high heat transfer. This will take some head pressure to obtain. Above another certain flow rate, the gain in heat transfer tapers off. So you want to balance the total flow between loops so that they are all in the "high gain" window. With all loops returned to the flow center, this is not difficult to achieve if you have the right size of circulation pump.