I have been installing loops for a while and designing efficient systems. I just purchased a house in Wisconsin that is pretty much in a marsh. The water table is between two and three feet. I pulled a posts out of the ground this fall (during a relatively dry period) and the holes filled with water within a minute. Within six inches of ground level. I am thinking this could make for good heat transfer. I have a large yard, but there is a water easement going through the middle of it at an eight foot depth. Slinkies or any other horizontal application would have to be less than 75 ft in length and there are utility lines that would further inhibit excavation. I just don't know how to calculate my loop length. If I just dug holes into the water table and buried three hundred foot coils for example like you might to on a lake loop. What kind of transfer could I expect? There is soil down there so it would not be as efficient as a lake. I am trying to design for 60,000 btu/hr heat loss. I should also mention that I pay a yearly flat fee of $125 for my water from a small water district servicing 60 homes. There is a large drain on my property that was put there by the district, so an open loop crossed my mind. thanks

You would have frozen ground in no time.
You need to know the BTU/h load then any design program can give you loop length for saturated ground.

I was not planning on digging a few feet deep. I was planning on going eight to fifteen feet deep if possible. My electrician and I just drove some grounding rods into the ground and it was tough going for the first foot or two and then they went in very easily after that. I can't imagine that the ground freezes in a marsh at six feet but maybe I am wrong.
Thanks

Since the heat pump will be extracting heat  from the loop, the ground will freeze around your loops if you just bury a coil of pipe in the ground, even if you went 100  feet deep.

Since the ground is saturated,  you won't need as much loop as you would in dryer ground.

Just burying a coil of pipe in the ground will not work.

Thanks,
So can I somehow calculate for the presence of this supersaturated soil or is it just soil. Does a marshland have better heat transfer than that of more common ground. If so how much?
I have not come across a situation like this and your help is appreciated.

Do you have a loop design program?

Yes. I guess I just was hoping that my situation would be closer to the heat transfer found in a pond loop.

If you can get a shallow well or reverse drain to work, you could run open loop.

Hi and welcome,

Please be advised that the number one failure of geo systems are designs that get to creative or cute when it comes to the heat exchanger.  I am as guilty as the next guy when it comes to getting more for less, but your gshx should not be one of them.

Hooking an open loop up to a central water supply with a flat rate for usage is not ideal either.  It may hasten your water district to a costly well replacement which will surely increase your rates.  also I am sure someone monitors the distribution, when the meter starts spinning at twice normal there will be an investigation to find the consumer of tat volume.

The fact that you live in super saturated soil may make your conductivity very high.  If that is the case you can reduce the cost of the gshx based on a reduction of pipe installed.  If your area is mud rotary drilling territory vertical would be an option.  If the soil is that wet, a shallow supply well that yielded enough capacity could be used for a pump and dump.

If you have been doing geo other places, go down to the local hvac bar and meet some people from the marsh who know what works the best in the marsh, the money you save from there advice will be your own.

I'm betting there are no individual meters since they are expensive to install and read.

Open loop could easily multiply household use by 10x, and the district system probably isn't designed for that and may have rules against it.

I'm not sure how you'd go about digging a trench 8+ feet in very wet ground - I'd expect sides to cave in. I believe anything over 6' isn't safe to be in owing to cave-in danger, even in dry ground. I believe OSHA requires shoring at deeper than 6' if anyone is to enter the trench.

trench boxes and pumps make for expensive trenching , you may find pump and dump or vert wells are your best options.
I had a problem in a similiar situation and ended up going to vertical wells after allmost a day of cave ins
as far as design sat. sand if different then clay or other , and you never know whats under that

Saturated ground has a much higher heat of conduction than soil. A coil in the marsh will not act like a coil in the pond. In the pond the water is much freer to move and you get the benefit of convective heat transfer due to water movement. The loop should be shorter however due so improved conductivity. However, the pipe wall will still provide significant resistance so the loop will not be 50 percent shorter.

The wells are a good idea. Another might be jetting in 20-30 foot wells if you don't want to go open source.

Seems like it would be very cost effective to use shallow well(s) for an open loop system. Something as simple as well points driven say 10 ft deep into the marsh would probably give you plenty of water.

Why not a vertical loop. Checik out www.kelix.com

Beware water quality in an open loop, esp. in case of shallow wells

Engineer, I've heard of scaling issues with hard well water in open loops but from your post it sounds like shallow well waters might have other issues besides hardness. Can you expand on that or send me to a link?

Nothing specific, just my sense that shallower aquifers may be of lower quality and variable availability (droughts)

Near surface waters should have much less hardness (because they haven't been in contact with limestone).

If the soil isn't porous, you might have to dig a big pit and fill it with sand to get a well point to work.