Geothermal Heat Exchanger

I'm planning on putting up a nice new shop up here in NW Montana. Exploring heating options I did some research on Geothermal heat (via heat pump to forced air) and it was expensive as heck. I also have experience with radiant-floor heat, but the systems up here don't work all that great due to the rather absurd cold and wind we get.

Got me thinking of using the chilly ground temp up here (my water is consistently under 45 degrees from my well) to help with some heat exchange situations. In the summertime I use most waste water to irrigate gardens, but in the winter time I hate putting it down the septic. I'm big into conserving water due to my shallow well, and was thinking that if I had a large coil of pipe buried 10 or so feet deep (frost line is around 6 ft), I could use it as source of the cold side for a plate chiller, or recirculating an antifreeze solution through jacketed fermenters, or something neato like that. The cost wouldnt be much as I am doing most of the construction myself and could simply dig an extra hole with the excavator and bury a bunch of PE pipe, maybe even with radiant floor-PEX inside it as a protective measure.

Crazy? Any engineers want to weigh in? What kind of pump would I need to push the antifreeze solution around? Or is this just flat-out silly?

Dry soil is a lousy thermal conductor, so if your loop is sitting in that it will heat up pretty quickly. If you want to extract a decent temperature differential for any length of time you need to get your loop down into moving ground water.

I have a home up in the White Mountains in Cow Hampster heated with geothermal. We have three 400' stainless coils that reach down into an underground aquifer below glacial till. It works very well, but it wasn't cheap to install. It was installed 15 years ago and I think the investment recoup took the best part of that, compared to the cheapest alternative...

Cheers!

https://www.dropbox.com/s/hp5ierskh8pz1l8/Geothermal.pdf

This has the information you seek. I agree with the above statements. Your system will be limited by the heat transfer with the ground. One good idea would be a back of the envelope calculation to decide what the maximum load on the system would be, say to bring some quantity of boiling water down to a desired temperature. It may turn out that the volume of liquid in the cold segment would be enough to remove the heat from whatever you needed and the time between these events would be of sufficient duration such that the time scales for heat transfer with the ground become insignificant. Some what of a thermal mass argument.

If you can inject water back into the well (seems to depend on where you live), you could run a clean water loop from the well and dump the hot return back into the well. The thermal gain of the well water will not raise the well temp much.

Here is a reference:
http://www.in.gov/isdh/23258.htm#D2

Joel

rosienej said:

If you can inject water back into the well (seems to depend on where you live), you could run a clean water loop from the well and dump the hot return back into the well. The thermal gain of the well water will not raise the well temp much.

Here is a reference:
http://www.in.gov/isdh/23258.htm#D2

Joel

Click to expand...

I dont know if its the same in other states but here in NJ those systems actually have 2 wells. A feed well to supply water to the unit and most of the time to the house as well. Then they have a separate well that is pressure sealed at the top to return the water back to the ground.

In Massachusetts open loop systems (supply from one well and return to another or supply from and return to the same well) are basically not allowed. I know that septic systems can be a concern and overusing them is not good. Just burying a coil in the ground below the frost line is not the solution, It might be if you were going to run a hundred feet of tubing vertically or horizontally, but a small coil of tubing in a small area will most likely heat the immediate area quickly and be of little effect. If the main concern is the septic system I would advise looking into a small process chiller system. No idea how much one would cost.

Seems like alot of work....why not just put a pre-chiller in a bucket of snow during the winter time? I'm assuming you have access to snow in MT.

Instead of having it directly in the ground you could put a sealed container full of a fluid with a sump pump to re-circulate through your chiller. That would use the cooler natural outside temp with a specific amount of liquid that would be re-usable for each brew.

Does your well make less water in the winter than in the summer?