700 foot well, 6" diameter, no water

Discussion in 'General Discussions' started by jeryder, Feb 2, 2009.

  1. jeryder

    jeryder New Member


    Building a new home in spring in north western ill. Can someone tell me a good contractor. And what are the cost saving of geo versa regular heat and cooling.
  2. Looby

    Looby Member Forum Leader

    What are your "regular" heating/cooling options?

    What are your local fuel prices and electric rates for the above?

    What's your electric rate, assuming a geo heat pump?

    I'm saving over $2500/year compared to oil heat and conventional A/C,
    but your mileage may vary. Also, consider the intangibles -- such as
    CLEAN heat with no combustion, no smoke, no odors, no CO detectors,
    no oil/propane tank, and relatively stable electric rates (compared to
    fossil fuels).

    If you roll the incremental cost of geothermal into a mortgage, it might
    well reduce your total monthly outlay for mortgage+utilities.

  3. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    If you mean spring 2009

    You better hurry. The use of geo is not easy to add late in the construction game. I use water to water heat pumps with radiant floors and high velocity a/c.
  4. jeryder

    jeryder New Member

    Natural gas or electric, will have to wait for next bill for prices. Still would like to talk to someone in northern illinois to see how a geo works for them. We have lots of time the ground is still as hard as a rock here, will probably be mid april before we start to build.
  5. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

  6. Waukman

    Waukman Member

    I am in Southern Wisconsin (metro Milwaukee area) and installed a Water Furnace in 07. This is ending my second season and things are working well.
  7. Howard Ek

    Howard Ek Member

    A client of mine proposes to use this well as follows:

    Drop 2 each, 1-1/4" 200 psi PE3408 pipes with bullet U-bends on the bottom, grouted in place.

    1.Will it fit? out-to-out is 3.75".
    2. What about the pressure (200 psi = 462 feet)?

  8. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    2 each? Does that mean two u-tubes = 4 pipes or does it mean one tube=2 pipes?

    The ability to grout will definitely influence the outcome as well.

    As to psi - if you are going with a non-pressurized flow centre; yes, eventually the pressure of the grout will collapse the pipes. If you are pressurizing your system, then you will be able to hold the pipes open. Some math to calculate the pressure of 700' of grout will be required - hint, it will be a lot.
  9. Howard Ek

    Howard Ek Member

    4 pipes, with a non-pressurized flow centre. We would have the pipes filled with water before we start.
  10. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    I will strongly suggest not using a non-pressurized system for boreholes at depth. The water column is not going to match the pressure of the grout column.

    This is a phenomenon starting to show up on commercial drilling jobs when things get delayed, and we'll see some guidelines in a few years regarding this.

    At the very least the pipe columns become "less round" under the grout compression. This effects heat transfer %'s.

    As to the 4 x 11/4 pipes in a 6" sleeve. Grab a few ends and see if they fit - I think that it will be quite tight and then you need to figure out how to get a tremie line in there as well.
  11. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Two thoughts, both off the top of my head:

    1) I don't see how a 2nd u-tube in the same hole does much good since either U tube would overwhelm the ground immediately surrounding the other. If this were acceptable, there would be no 15' separation needed between the more typical single U-tube bores.

    In other words I'm betting that about the same heat transfer would be possible in that hole regardless of number of U-tubes in it. More tube length means higher pump power, though.

    2) filling the U with water (and capping the ends) should help keep grout from crushing tube. However, a 700' column of water will result in 300 psi at the bottom of the U-tube sitting in an open bore. Is the pipe rated to not fail at 300 psi?

    A solution to that problem might be to stage the water and grout. Add enough water to just half fill the U-tube, and then grout only halfway up. Let that grout set and repeat for the upper half. Could be done in thirds or quarters depending on the pipe's pressure rating.
  12. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Engineer, pairing u-tubes is not unheard of. Not all that common, but you can design for it.

    A water column has a psi, granted, but minor in relation to the grout density. If it was a closed system then it would equalize. In an open system you end up "compacting" the pipe boreholes.

    The easy way to know this is happening is to order a set volume of fluid to add to the ground loops (based on design) and see how much is left over.

    For us, we won't do unpressurized systems anymore and we won't leave vertical pipe unfilled for any period of time.
  13. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Ball State University, the largest Geo retrofit in the country, is installing two ubends per bore hole.

    The benefit is small, but there is some gain.
  14. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    While I have never been an advocate for putting 7/8 of loop in an 8/8 hole, I would increase the size of one loop to 2". The wall thickness of the 2" pipe would help with crush rating issue, and I am guessing it would yield the same as two 1 1/4 loops. One loop plus tremie line is far less problimatic than two loops plus tremmie line.
    The one side note I would make is that to install a 2" by 600' loop you are going to need a pipe straightener or assymble the u bend on site using straight lengths of pipe. You will also need a braking system if you fill the loop with water and insert into a dry hole. Gravity is unforgiving and the loop "will" be damaged when it crashes into the bottom of the bore if it is dry.
  15. Looby

    Looby Member Forum Leader

    With 2" pipe, be careful to keep an eye on GPM and antifreeze
    type -- and the corresponding Reynolds number.
  16. MT Pockets

    MT Pockets Guest

    I’m sure someone is going to tell me different but a 700’ bore to be used for Geothermal is just simply not common at all. Next, if you get a pipe manufacturer to custom make a 1 ¼” loop (or any size) that big should be shamed; but more importantly they are not investing any interest for the end user. Any loop installer that really prides themselves with quality better be testing the loops with water topped off with air pressure before inserting the loop into the bore hole. Then the loop will be filled with water before its inserted into the bore hole, perhaps some of the water is dumped out so the loop isn’t so heavy but the pipe is buoyant and has to be pushed down the hole so the water weight is going to help. Most installers have a contraption to insert the pipe into the ground without manual labor. In the event of a dry hole at 700’ I would personally not go that deep. I don’t know the conditions or the geology of this project so I really don’t want to comment any further. But I do want to remind everyone that in normal conditions (wet borehole) for every psi/foot increase inside the pipe going down the borehole there is an equal amount of pressure on the outside of the pipe as well.

    Now on the topic of pressurized verses non-pressurized it simply does not matter. A pump is designed to pump fluid within its performance curve regardless of system pressure or regardless of loop field type.
  17. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    Think you're a little off track here.

    All boreholes are grouted, and it is the pressure of the grout column having an effect on pipe compaction.


    urthbuoy I think you may be mistaken in your thought process. I would really like to see what data you have spoken of to prove this? I think you may be forgetting the fact that these pipes will have water in them. Now on to the discussion of a 700' bore hole I would not recomend it but if you are looking at doing something of that nature you may want to step up the SDR value of you pipe.
  19. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    My original post has been edited (not by me) and the details removed - which I find a little disconcerting. GT, I did have the numbers shown on pipe pressures at depth. Now it just looks like I'm arguing with MT - not the case.

    A pipe won't collapse with water maintained in it. But water needs to be in it and held in it. An uncapped u-tube will collapse with the grout column pressure at depth. During normal construction there is a lot of potential for uncapped u-tubes, u-tubes with air, and unsettled boreholes being connected to a non-pressurized system. Those are the issues. It can all be done right - but it can also be done wrong.

    To add to the issue, tightly wrapped pipe bundles tend to produce oval pipes. These are less resistance to collapse.

    There is a difference between pipes pinching off and pipes collapsing but still allowing flow. I tend to believe, while rare for pipes to pinch off, it is not rare for pipes to collapse and generally decrease the volume of the fluids in the field.

    This is commonly detected by ordering a known amount of antifreeze for a system (based on a design loop field) and seeing how much difference there is on the as-built results.
    Last edited: Mar 31, 2010

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