switching from vert. to horz.

Discussion in 'Geothermal Loops' started by bjl, Nov 28, 2014.

  1. bjl

    bjl Member

    I have a new house under construction and would like some clarification on quotes from a couple contractors. I already purchased the air handlers, Miami heat pump 3.5 ton 2 stage and a 2.5 ton, on the advice of one of the drillers. The company that did my manual j and d told me that vertical was the most efficient way. From what I am reading this is not the case. In fact his quote was about $20k more that getting conventional units from my younger brother.

    Another installer wants to dig a deep trench and coil the ¾” hdpe in it, backfill a few feet and coil back towards the house. The trench would be 90’ long and 10’ deep with about 2000’ of pipe in each one. They said I need 3. Does this sound right?

    Another wants to just lay the pipe at about 6’ in straight runs. He has a trenching machine so it would go fast but it would mean a lot more trenches.

    I am in southern Louisiana and the ground has a lot of clay at 5' and deeper and i start getting water at that level also. I also have read that using 800’ per ton is a safe number but what about the sq. ft. I have seen nothing on how many sq. ft should the loop field be in per ton. I understand there is no set formula and every job is different.

    i have seen where you can make a large bore hole, say 18" x 20’ deep, and place a coil tower in it with over 100' of pipe on it. i am no pro, but seems to me that the center of this coil would get hot or cold and the system would lose efficiency. more piping would have to go in to compensate. any thoughts on these towers? i have not seen a lot of information on them so i guess they are not widely used. I have also read about hdd, which I would rather do, but there is no one around here that has done this for geothermal purposes. I would be concerned that the grouting in would not be done properly.

    if the ¾” hdpe was stepped up to 1" or even 1.25” hdpe could the loops be shorter and hooked in series or will the friction loss be to great for the 1/6 hp circulater.

    can pex with the expander rings be a reliable substitute for the loop field.

    on another note, the desuperheater. with the tap water being pumped through the unit, would this cause scale to build up? i do plan on putting in a jacuzzi later on. for this application, would it be better to reroute my loop field in the summer to a heat exchange for the tub, or reroute the desuperheater with a thermostat so when the buffer tank hits its temp it auto switches to the tub? the reason for this would be that it is tap water and not a toxic mix.

    i apologize for questions being all over the place, i am kinda new at this.
    any and all help is greatly appreciated.
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Go to the home page and try the search function. We also have a check list and guide to help you narrow down the scope of your information request.
  3. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    This not a good idea. Don't even consider it!!

    The amount of pipe that is needed in the ground is a calculated number based on the requirements of your project. This is not a question to be answered by browsing the internet.

    The way you put that pipe in the ground is decided by what ever is most cost effective for your project. Again the answer will not be found online.
    Mark Custis and waterpirate like this.
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    No, Vertical is not more efficient than horizontal. I would even argue that horizontals are slightly more efficient due to a slower swing since they are connected to more ground mass. The have more thermal inertia, which keeps them warmer in the winter and colder in the summer.

    2000' of 3/4" pipe is also a bad idea, pressure drop (flow resistance) is too high.

    6' straight trenches sounds OK

    water at 5' sounds good too. The wetter the better.

    Clay sounds good too.

    Coil towers may work, but what an effort.....

    Yes, larger pipe means lesser flow restrictions.

    No pex with expander rings suitable for the loop field.

    Good question with the Desuperheater. However, in real life they rarely fail. Don't make the DSH install too complex!
  5. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    The higher efficiency of vertical loops simply means you can collect/reject a similar amount of btu's with less feet of pipe. The operating cost however is nearly unchanged though can favor one or the other depending on a variety of conditions. Properly designed loops should all perform about the same. Make sure your heat pumps qualify for the tax credit.
  6. bjl

    bjl Member

    I have read hundreds of threads in this forum and i just want to compliment you guys on how informative you are. Thanks for the information and keep up the good work.
  7. Bergy

    Bergy Member Industry Professional Forum Leader

    Just to clarify, vertical loops usually extract more BTUs (or reject) per foot. However, one typically has more feet of pipe in horizontal loops. Thus the overall performance does not differ, and now the higher inertia actually can favor the horizontal application, since more pipe is connected to more mass of ground.
  8. bjl

    bjl Member

    I understand why the claim of being more efficient now. Thanks for the clarification. Another oddball question. Has anyone tried using thermally enhanced grout in a horizontal loop. Would this possibly reduce the amount of loop field needed or is it just throwing more money in a hole. Literally. I dont know how much the stuff costs, but it would have to outweigh the extra digging and pipe of course.
  9. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Yes, and I do not know. The graphite based grouts were initially developed for horizontal applications. How much better it is than pulling back with a straight bentonite based slurry is unknown to me.
  10. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Just to clarify, grout is there to fill air gaps in drilling applications. If you are talking trenching, I see no point in grouting.
  11. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    I agree that enhanced grout in a trench would be pointless and a waste of money
  12. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Grout in a trench would be better than plain sand.
  13. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    "Grout in a trench would be better than plain sand."
    True dat, but it would be easier and cheaper to add a few feet of pipe than another step in the installation.
    Worst case soil TC is greater than grout and it impedes. Best case grout TC is greater than surrounding soil and improves the size of surface in contact with soil.......of course you could do that with larger pipe diameter or longer loops.....

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