Cheap Geothermal System





Introduction: Cheap Geothermal System

I wanted to see how cheap I could build a working geothermal system.  I had heard a lot about how expensive these systems could be,  so I did some research into how these systems work and decided to give it a try.

You can find lots of information about geothermal systems by searching the web.  I found an instructable where someone used the temperature of their well water to cool their house.  It made me think " If I could tap into this temperature difference in a closed loop system it could be useful " so I started digging.

Step 1: Digging Your Hole

Digging a hole like this can be very dangerous.  People die in small hole collapses everyday.  Even if you have been trained to dig holes like this bad things can happen.  Do not dig a hole like this,  in most places a four foot trench would be fine. 

To get the full benefit from geothermal properties do some research on your area to find the best depth for your zone.  Four feet would have been fine for my area,  but I wanted to try out a theory I had and by the time I got to eight feet ,  I had two feet of cool water in the bottom of my hole.  Water makes a pretty good heat exchanger and because I live on an  island I hit water pretty quick.  This lead me to the decision of setting my loop in such an unconventional manner.

Do not try this at home.

Step 2: Your Loop

For my loop I wanted to use the cheapest pipe I could find.  It turns out, you can find this type of pipe at any home improvement store for only 10 cents a foot.  Plastic may not be the best heat exchanger but with a slow enough pump 200 feet of it should do nicely.  If I had some help digging or a backhoe I would have probably gone with 2000 feet,  but it's just me and this is just an experiment. 

Step 3: Piped Up

After your loop is in you can attach your pump and heat exchanger and start playing with it.
For my pump I used a fuel pump from a 90s model honda civic.
For my heat exchanger I used an after market radiator from a 90s model honda civic.
And for my air handler I used a stock radiator from the same 90s model honda civic.
The system runs on 12v and you can hear the water trickling through it as it gets cold.

Have fun, 

Be safe,

And remember,  every dime you save doing something sustainable,  is money you can spend elsewhere to make the economy strong again.



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    26 Discussions

    i made it too. just used InpliX instructions.

    I have a small back yard but the entire neighborhood drains through it making it a great wet thermal mass; how much less digging can I get by with?

    1-Why did you use oil pump from the car, instead of water pump from the car.

    2-How fast water need to move in the loop?

    3-how force full pump need to be ?

    1 reply

    He used the fuel pump to move water, not an oil pump. The water pump was not used because the water pump of a car spins off a timing chain/ belt making it impractical for just moving water whereas the fuel pump is an inline pump and only needs 12v to move water.

    Water wells work better than a trench because the water in them is usually flowing in an under ground stream. This will carry off heat efficiently .

    looks great like the rest would like more info.. I was wondering would I be able to use my old well. My house was built before city water went in the well is still there and was functional as well water the pipes still there the jet pump was removed just wondering if that could be used.

    I would like to know if I could use this system for my green houses? they are 10 by 40 by 10 and made of 4 and six ml plastic sheeting. i live in southwest wa 25 miles east of woodland wa in the cascade mts and we get temps of 20's to mid 30's in the winter usually. will i need to go 4 ft deep and go the width of the greenhouses(10ft) the length(40) to get maximum efficiancy out of this unit? pls contact me with info on this pls.

    One thought. I know you're just fiddling here - I'm a big fan of the 'experimentalist' school of thought', i.e. proof of concept first, and have fun, THEN go back and calc it out ;-). What's interesting though, besides the obvious calculation of what kind of actual heat BTUs you can get (which here is less calculating and more measuring): what's the pump electric costing you? I don't even mean fully costing it - but it'd be interesting to, say, stick a power meter on the pump, and have a flowmeter in the loop, and figure out how many kwh it 'costs' per gph.

    Another idea, since you've mentioned your open uninsulated shop -- it might be fun to just throw a cheap plastic-sheeting 'painter's frame' up around it. Not much for insulation, but at least you don't have airflow. You could even improv something quick-n-cheap -- pretend you're building a kids' 'fort': put some chairs or stepladders around it and throw a $7 Home Depot clear plastic 'dropcloth' over it. See how long it takes for temp to drop x degrees, guesstimate air volume under the hood, extrapolate to shop...? Then divide by feet of tubing, look at average depth, soil temp at that depth, and you could SWAG how many feet of tubing it'd take to cool your shop in how many hours, no? Also look at temp differential at different depths? (Apparently you get LOTS more efficiency for even small changes in soil temp.) Although the shallow water table probably makes that moot once you hit it, I *think*...?

    One more thought: I *think* your concern about metal is totally correct -- *except* maybe for copper, which, not only happens to be THE best heat exchanger (other than pure silver ;-) -- but is NOT attacked by acids other than nitric. You can put it in conc. hydrochloric just fine. And metals don't mind bases, pure electrochemistry.

     Any chance you can post pics for the following? :
    pieces by themselves
    hooking the tubing up... to what? How? where? to what part?
    hooking up the radiator, etc., including part-to-part details.

    I'm going to assume this simply pumps in the cool air or cool water from the pipes, then the fan blows over the radiator holding the stuff, then the fan blows over the radiator.  When this is done, however, where does the cool air/water go?   In order to be a heat EXCHANGER, you have to exchange the heat with something, and that something is usually sent back somewhere.  

    A bit more detail would have been great & made this an A+ project.
    I look forward to these details so I can get a better handle on what this all does.  I live in the desert, so something like this might be JUST what I need!!

    If you don't care to post them, please feel free to email me drawings or whatever you have to  sellen   AT   aol   DOT   com .
    Thanks!! I'll be waiting!   :)


    2 replies

    Next chance I get I'm going to take a bunch of pictures.  The system is empty right now and would give me a great opportunity to share more about the system.

    when the water in the loop gets to the radiator it's cool,  from running through the loop,  as the fan blows across it,  the temperature of the air cools down,  but the water "leaving" the radiator is warmer for having pasted through it (temperature exchanged,  from water to air).  This warmer water is then pumped back through the loop and cool again,  the system keeps repeating (closed loop).

    I'll be posting more pictures soon,  the garden,  wine and giant wind turbine are taking up a lot of my time right now,  not to mention work :(

    How was the performance of your geothermal unit, Did it work and can I also get more information? Thanks

    hello dear
    i want to apply this idea "Cheap Geothermal system"
    but i need some calculation for heat exchangers
    specially hot can i calculate the amount of heat rejected or absorbed by earth connecting
    and refrigeration effect

    plz tell me if you want to help me or no

    hello dear
    i want to apply this idea "Cheap Geothermal system"
    but i need some calculation for heat exchangers
    specially hot can i calculate the amount of heat rejected or absorbed by earth connecting
    and refrigeration effect

    plz tell me if you want to help me or no

    Plastic may not be the best heat exchanger but...
    That is an understatement.  Plastic is an insulator.  Yes it is inexpensive is such a poor heat exchanger that I'm surprised you were able to get any effect at all.  Any kind of metal pipe will be much more effective down in the hole.  You might use metal only at the bottom of the hole and and as your top-side radiator and then use plastic everywhere else. 

    We made a similar heat exchanger with the same pipe when I was a kid.  It was on our roof in the California desert and used to heat water.  It was dreadfully inefficient. 

    I moved from Dayton in 1980.  At that time the air force base was experimenting with geothermal heating and cooling for huge indoor areas.  I never found out how that worked. 

    2 replies

    I realize I'm coming late to this party, but with geothermal the insulating qualities of plastic are not a big deal because they are roughly the same as the insulating qualities of soil. If you are pulling temp differential from the ground itself, then the wall of the pipe is no different than a 1/4 inch of dirt that you're pulling temp from.

    In this case, the pipe is in water, so you might gain some efficiency from a more heat conductive material but with a little extra tube down the hole, that insulation is easily overcome. Remember insulation doesn't stop heat transfer, it just slows it down. More surface area will overcome the slow down, thus more tubing means more heat transfer.

    I totally agree,  and I would have loved to put a hundred feet of aluminum or copper at the bottom of my hole,  " BUT "  the ph is funny around here.  I've been doing plumbing work for a good number of years now and I've see terrible things happen to metal pipe in as few as 13 years.  So unless I could coat it with some kind of jelly that could keep it from corroding I just could not see putting something into the earth that I may have to dig up again.

    Besides Plastic is  the standard for this type of thing,  here is my favorite geothermal website (if you have one please share)
    If you scroll down about a quarter of the way you will see one of my favorite geothermal loop configuration.  

    as for the geothermal the air force installed.  I've had people sit down with me and on paper the equipment is so expensive and the pumps are so inefficient,  that really big systems over the long run will only pay off if they are over a fault line.  Sorry to say but that's just more wasted tax dollars and the reason I had to see how cheap it could be done. 

    cool experiment ! Id like more pics of your radiator setups. I agree, a lot of the systems out there use some type of plastic pipe/tubing. I would imagine that once its buried it quickly assumes the temperature surrounding it. Are you using solar to charge the batteries? 

    That hole does look REALLY dangerous, it would be safer and allow more tubing to to do say a 6x6x6 or 8 area or even 10x10x6 or if possible a long trench. I know that sounds like a lot of work but you can rent a skidsteer tractor fairly cheap. That being said, I understand this was meant as an inexpensive experiment.

     How portable is your system? Could you set it up in a different enclosed space like an old regrigerator, a car or small bedroom and measure its effectiveness?

    1 reply

    When the "Giant Wind Turbine" is done I'd like run the system off of her,  right now it runs on an old car battery charger.

    The trench Idea is probably best,  "When" I do this again,  I will be looking for a ditch-witch that will hit 4 feet.  I'm pretty sure you can get cable/pipe laying attachments for them,  2000 feet would go by in just a few hours (as long as you don't hit a VW sized boulder).

    As for the "old refrigerator" idea I love it.  There are to really great instuctables about building very well insulated containers for refrigeration and I had been looking for a reason to build one myself.  I could just build it around what I have here to keep beverages cool here in the shop.

    I love this website.

    If you use anything besides water in your pipes... do NOT let the stuff leak.

    Common practice in these parts(where some people still use wells) is to fill the hole back in using cement. course, we don't hit water till MUCH deeper than 6 feet. ;-) The other benifit, for us non-water people is... solid concrete is a better heat transfer medium than plain soil...and protects the pipes from shovels too.

    I'm thinking, you're sized radiator would be just about perfect for a geothermal keg-a-rator.