Turn a sinkhole into Geo?

Discussion in 'General Discussions' started by Jake T Robinson, Jan 20, 2017.

  1. Jake T Robinson

    Jake T Robinson New Member

    Hey folks, trying to assess a potential opportunity. We have a huge sinkhole in our backyard, not the type you see in in Florida that tends to grow, this one has been stable for 30 years or more with Big Trees growing out of it. It actually is a window into a carst system of a huge underground cave system known in Tennessee as snail shell cave. I had a professional caver do an initial assessment of the window which is about 20 feet below the surface at the bottom of the sinkhole from there it drops straight down into the cave with a 25 foot shaft. He has not been down into the bottom yet, he will explore later as he has mapped many many miles of this Cave System.

    My question is, can this be an opportunity to hack geothermal by running pipe down the 25 that shaft and then going horizontal for a good ways assuming the cave runs this way? The caver says the main floor is about 70" underground. He showed me a map and pointed out thus us a "main thourghfare" running right under my property.

    Would this save installation costs or would there be obvious drawbacks to doing this?

    I am heating/cooling a 100 yr old school house (3000 sq ft) with 12" ceilings. I have to 5-ton Electric HVAC heat pumps that cool roughly 1500 square foot each.

    Before I had foam injection insulation pumped into the walls (before we actually moved in) I ran the electric heat pump to keep a constant temp while my floor guy refinished the hardwoods. The hot water heater breaker was off, no one was living in the property, only the HVAC system and some lights were on and my heating bill came back at $799! Since we've had insulation installed our last month's bill with some really cold Temps, with three adults using hot water, bathing, cooking laundry excetera was a little over $400.

    Still very high but the foam insulation was doing a good job. However I would like to not the heck out of that electric bill with geothermal.

    Would love to get some feedback, about what you think could be done and would there be a savings with this opportunity. what type of hardware or system should I use. Can I continue to use my existing HVAC system with a geothermal combination?

    I'll be happy to answer any questions or fill in any details to figure this out, thanks
  2. Jake T Robinson

    Jake T Robinson New Member

    Hmmm, couldn't figure out how to edit as I spotted a few typos

    *two 5-ton HVAC units heating 1500 sq ft each
    *pointed out this is a "main thoroughfare" running under our property
  3. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    This is certainly a unique hack situation. Does the shaft have any flow? Does the chamber at the bottom of the shaft have any flow? What are the dimensions of the shaft filled with water? My gut says a slinky type arrangement could be made of copper or hdpe to make the exchange, or use a slim jim type plate exchanger.
  4. Jake T Robinson

    Jake T Robinson New Member

    Hey Eric,

    Thanks for the response.

    The sinkhole stays dry, (no flow to very little water flow) most of the time. It has to be very specific conditions before water actually flows down into the sinkhole. Sure, I guess when it's raining there must be some bit of water but for a visible flow it has to have rained for many days and the ground has to be saturated and then a really strong rain to occur in order for enough water to collect and flow into the sinkhole which only happens maybe once a year. I don't know about whether or not there is continuous underground flow near the cave floor - we'll find out once my caver friend does a thorough explanation.

    When my cave friend goes back down I will be asking him to assess these types of features. He says the main cave floor is usually huge an open and you can walkthrough erect without any problem.

    The shaft that goes down at the bottom of the sinkhole is approximately 3 to 6 feet in diameter he was able to easily repel down into it about six or seven feet until he reached the "debris plug" - he didn't go any further because he wanted to clear the plug debris which is going to take a little bit more work with the help of his partner.

    I'm thinking a plastic pipe could be run down and then turn and go along the cave floor in either direction.

    Assuming I am not restricted in distance do I need to have water flow in order for proper exchange?

    I'm not familiar with a slim Jim plate exchanger, I'll Google it,

    My caver buddy had specifically mentioned geothermal as a possibility when he first looked at the window - at the time the light bulb didn't go off... Last night I was at a monthly "maker's meeting" and the sinkhole subject came up and immediately it was commented that I should consider geothermal.

    I'll be skeding my caver to inspect with this in mind.

    Thanks for the feedback.
  5. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Air is a poor medium. So not the most effective idea. Pipes are in earth or water.

    There is a passive air tube world out there. I went down this rabbit hole for a bit with a client, but I'm not comfortable with the untreated air part.
  6. Jake T Robinson

    Jake T Robinson New Member

    Thanks for the feedback, maybe there is water
  7. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    My bad,
    I ass summed all sink holes are wet like the ones I am familiar with. Air is a poor conductor. Need to find water to make it work, or go back to a traditional exchange method.

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