Geothermal system types - water (ground) source vs direct exchange (DX)

Discussion in 'General Discussions' started by sjohnson, Mar 18, 2009.

  1. sjohnson

    sjohnson Guest

    Hello all-

    I am new to this, but i have a basic understanding on how geothermal heating/cooling works.

    My question is with Geothermal heating/cooling types, I have spoken to one installer who uses the refrigerant to transfer heat directly back to the ground and others which utilize water/antifreeze solution.

    Is one type "better" than the other, or does it come down to cost.

    I was told the "DX" system uses 3" holes drilled in a conical pattern out from a manifold 65-70' deep with the copper tubing carrying the coolant directly into the ground. the others mentioned 200' holes drilled at a much larger diameter.
    thanks for any help you can offer.
  2. wrice3

    wrice3 New Member


    on your soil type. I don't see you have your location noted? Some places like where I live, the soil will eat the copper pipe, so the closest DX installer is an hour away and no one where I live does DX because of the soil. So all the installs here are plastic pipe with MeOH-H2O. The most important part of all this is the loop design, so if the DX installer knows what he/she is doing and can design an appropriate system that will not leak, I would consider that. But definitely go with an experienced installer, whether it is DX or not.
  3. sjohnson

    sjohnson Guest

    thanks, i should have been more specific.

    Rhode Island is the location of the site, the building is a 4000sqft commercial post and beam construction SIPS insulated. We are planning to go with radiant floor heating and ducted A/C. (Our intent is LEED Gold) The DX company is out of PA, they claim to have successfully installed as far north as Maine.

    I have never heard of DX type Geo.. possibly because of Ph issues?
  4. ClarkT

    ClarkT Member

    Copper refrigerant lines will NOT leak in the ground unless it's acidic and has no form of cathodic protection.

    If the pH of the soil higher than 6.0 (approx. 5% of the land area of the U.S.), there will not be corrosion on a copper refrigerant line in the ground. Refrigerant is an inert gas, and therefore it will not cause electrolysis from the inside of the copper. In areas where the pH of the soil is 6.0 or lower, EarthLinked has a CPS (corrosion protection system) available. This is an impressed current cathodic protection with a 50 year life on the anode. After 50 years, simply replace the anode.

    On any system, whether it's water source or DX, MAKE SURE that they are AHRI rated!!!!!!! Don't fall for something that's not. You'll likely get bit by it, if it's not.

    EarthLinked is definitely AHRI rated, Energy Star rated, ETL, and CSA rated, too.

    On loop design, EarthLinked already has a PRE-DESIGNED, pre-engineered loop. The only thing one needs to know is soil temp. There are maps and charts that tell that for most any area. It's a FARCE to state/think that DX needs loop design. DX does a different type of heat exchange than water source, and therefore can be pre-engineered. Because of that, IGSHPA is not even needed, and any HVAC company that understands proper load calculations and refrigerant systems can competently install EarthLinked.

    Obviously I'm pro-EarthLinked, as I've seen them work in VERY harsh weather (in Eastern Utah).

    As far as being better than water source, that depends on the application. For residential, EarthLinked has the most efficient closed loop systems available. For small/light commercial, the same is true. But DX does have some limitations for larger commercial, so it's not better there. On larger commercial, the best setup would be a mixture of DX and water source. Thus reducing the pumping needs of the water side, and reducing the footprint and drilling amount.

    So, for your home, I'd say DX would be better (AHRI rated). Don't forget the recommendation, though, that you use an installer who is credible and will perform and follow an accurate (not fudged) Manual J load calculation, and then follow manufacturer's recommendations.
  5. gabby

    gabby Member Industry Professional Forum Leader


    The soil survey for Rhode Island

    Published Soil Surveys for Rhode Island | NRCS Soils

    Contact your local office and they will help you with what you need to know...maybe even come over an run a free soil analysis for you....they do that in the Houston area down to 8 feet.
  6. sjohnson

    sjohnson Guest

    thank you for the info, i will look into the installer and product we select in great detail.
  7. Guest

    Guest Guest

    I've never understood why they can't run a DX system with some type of plastic pipe. There must be a plastic that can be used with refrigerant.
  8. sjohnson

    sjohnson Guest

    Good Question....

    My guess, Copper is a better conductor, and DX has a much shorter loop than water (ground) source.

    But that is a guess, im wrong alot, just ask my wife.
  9. Guest

    Guest Guest

    I know they make pex tubing with aluminum foil in it to fix permeability.

    But maybe copper tubing + zinc anodes with active (powered) cathodic protection is best for DX.
  10. Guest

    Guest Guest

    I find it odd that someone is designing a loop knowing only soil temperature.

    I would want to know soil thermal conductivity, soil density and the seasonal variation in temperature (or the depth).

    Seems like someone must make a test probe - stick it down to the planned depth and it could measure these things.
  11. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    DX designs systems with max loop length. ESES for instance may only be able to recover refrigerant oil 50' vertically while Earthlinked might go 75'. The system requirement based on certain soils might be 30' in some cases and 45' in others. In no case however is extra loop a performance killer, so they took the guess work out and max sized the loops. The technology works and as TLuck pointed out many HVAC guys are attracted to it as it doesn't require new tools or skills of them.
    Where I always bridle is on efficiency claims regardless of brand or type. I'm sick of claims (or even discussion for that matter) of superior efficiency. Test labs have little to do with real world. DX systems routinely have oversized loops. Water source systems might perform best with open loops in the winter and closed in the summer. 2 stage equipment is superior to single-stage, but operating cost improvement is miniscule.....
    Find your self the best installer with the best (long term) references and you'll be happy with your heat pump of any type.
    Good Luck,

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