DX Geo

fabmasterNovember 30, 2006

I am considering a DX Geothermal unit and can hardly find any info about them. I originally had my mind set on a water source system but as i intend to drill myself the shallower holes required for the DX system seem much more appealing. Does anyone know where I can find the PH values for my soil? I understand this is one of the main concerns with this type of system. And any other info that may be useful.

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What is a DX geo unit? Why are you worried about PH of the soil? The easiest way to determine acidity is to measure it?

    Bookmark   November 30, 2006 at 11:44PM
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To find out the PH of the soil in your area I would suggest contacting a geologist locally or contact the closest university in your vicinity for information. You can also try e-mailing IGSHPA at Oklahoma State University, IÂm sure someone there would know.

Where are you located specifically? How do copper pipes from the municipal water mains hold up; after how many years do they typically need replacing?

For what itÂs worth, you can always ask a manufacturer that makes both types of HPÂs. Should there be a PH problem in your area, theyÂd likely tell you and steer you to a HDPE liquid system. Speaking of which, any idea how far down the water table is?

I donÂt think this is a DIY project. IÂd rethink that part.

WeÂre into our 4th heating season with our Nordic DX geothermal GSHP and have nothing but praise for it - and the company that manufactures it!

On the link below, click ÂProductsÂ, then click ÂDX-Series.

Good Luck.


Here is a link that might be useful: Nordic DX Series GSHP

    Bookmark   December 1, 2006 at 1:05AM
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I am in Southeast Texas. I just had my soil tested for the foundation to be engineered maybe those guys can tell me? The system would primarily be used for cooling due to the climate here. It seems that there is more focus on heating with these systems than cooling is there a reason for this? The water table is around 80 feet. I wouldn't consider myself a typical DIYer I'm just not a full time professional driller.

    Bookmark   December 1, 2006 at 9:36AM
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Hello Fabmaster.

Probably your local county extension agent could tell you the pH of the soil,since it matters a great deal to gardeners, or you could go to a hardware store and buy a soil test kit, or some pH paper, and measure it.

I take it that a DX system is a ground source, closed loop system? If I understand your situation correctly (and I may well not) you want to tap into the earth's thermal mass by drilling shallow wells and recirculating liquid from pipes in those wells through your heat pump.

The efficiency of a heat pump is greatly increased in such a system IF the recirculating liquid is effectively in contact with soil, thermally speaking. Obviously, in your case it isn't flowing out of the pipes into the earth and being picked up again, but it's important that it spend enough time in as close contact as possible. If the soil is wet it helps. The coils or loops that are in these systems are usually plastic, which inhibits the flow of heat more than metals (but almost never needs to be replaced), so the transference inefficiency has to be compensated for with longer trenches or deeper or more numerous wells. It may be that your envisioned system requires metal pipes in damp soils, and the pH matters because these pipes would be more rapidly degraded in an acid soil.

The deeper you can place the conduits that are recirculating the better; the closer to the surface they are the more they are influenced by day-to-day variables.

So while you may drill shallow wells that will work with your particular heat pump better than if it were an air system it remains true that the deeper you can go the more efficiently your heat pump will run. Thus while the shallow well (or equivalent in long trenchs) certainly can work, the single deep well has its attractions, in that the water brought up from the depths is much less affected by surface conditions, has huge thermal mass (and thus inertia) and offers a much better counterpoint to whatever the sureface conditions are.

Thus, if it's really hot out side, and you really need your air conditioner to work efficiently, the system that goes deeper is going to perform better. You'd be tickled to have water in the 50's or low 60's to help your heat pump. Conversely, up here in Montana, where it gets really cold, we're quite grateful to be able to reach down 58 feet for our relatively warm (about 52 F at the moment) water.

I don't know what soil conditions are where you are but in some regions drilling wells is too capital and energy intensive for DIY'ers. Before you "try this at home" locate a few working water drilling rigs and observe their operation for a few hours. You may well see that it's doable, (or no!) and you'll surely learn a couple of useful things by watching.

Good luck to you; I hope you'll research your options and resources very closely. I'm a big (ground source) heat pump fan and I think you'll love yours if you decide to go that route.


    Bookmark   December 1, 2006 at 8:34PM
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I donÂt think thereÂs more of a focus on heating than A/C. A properly designed system will work well in both modes.

If you can hit enough water at 80 feet, AND if the water is sufficiently cool, below 50ºF, (which is not likely your case), you might also consider an open loop, passive cooling GSHP  THE most efficient means of cooling  BY FAR (EER as high as 118, according to specs)!! May also be the least expensive to install.


Any properly designed ground loop should be as efficient as any other configuration properly designed.

DX is a completely different GSHP animal. ItÂs not a liquid based system in the traditional sense. The refrigerant gas is directly circulated in the boreholes, which is why the pipes have to be copper. There is no secondary (liquid to refrigerant) heat exchanger, no liquid anti-freeze and no circulating pump required in a DX system. Because the refrigerant is in direct contact (DX) with the ground (circulated by the compressor alone) and because the pipes are copper (better conductivity)as opposed to HDPE, the boreholes required are about 40% shallower than for an equivalent HDPE liquid closed loop system. This results in a substantial savings in drilling costs. As well the boreholes are about 3 inches in diameter as opposed to about 6 inches in diameter for HDPE.

DX is mechanically a simpler system with fewer moving parts and less to maintain, but electronically more sophisticated with regard to its computer.


    Bookmark   December 2, 2006 at 4:12AM
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SR- Thanks for the clarification. The DX concept sounds exceptionally ingenious.


    Bookmark   December 2, 2006 at 3:39PM
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This is what I'm talking about. Nobody knows nothin about these things. Unless they have one.I've looked on line. I've called contractors. This just seems like it would work to well to be this overlooked. Thanks for the link fsq4cw. It is much to humid here for a passive cooling system.

    Bookmark   December 6, 2006 at 9:10PM
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Re: fabmaster

IÂll keep this short, but you can find more lengthy posts on this matter if you use the GW Search function.

The short answer is Nordic DX DOES work particularly well - when properly installed - in the right conditions (ph) for residential. People only want to work with what they know. DX is too Âout there for most installers. More is the pity; itÂs a simpler design and in fact easier to install and maintain. ItÂs like the VHS vs. Beta war. We all know that Beta was the superior design.

DX is not going away. There is a place in the market for it and with few exceptions; DX owners are just as passionate about their GSHPs. Personally, from my own first hand experience, I think theyÂre a brilliant design. Who needs a well pump anyways?


    Bookmark   December 7, 2006 at 1:35AM
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We are located in Newport, MN, less than 10 miles from St. Paul, and only 2 miles from the Mississippi. Determining soil ph is a problem: I want to know if it varies 68 feet below ground like it does from plot to plot in my gardens. For DX Geo, I understand that soil ph ought to be close to neutral. But we are located on glacial till. I've researched 11 water wells driven withing 1,000 feet and they are wildly different: one, 400 feet away, didn't hit bedrock atall at 170'. His neighbor, 100' feet west, hit bedrock at 20' !! All reported sand/gravel until (most) hit sandstone. Well water was hit at about 250'. Does the rock below the sand/gravel effect soil ph in the upper strata? Is it possible to determine soil ph in advance when drilling in a geologically diverse area within a neighborhood?

Bob in Newport

    Bookmark   February 5, 2007 at 2:03PM
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Re: Soil ph

Contact a geologist; see what you can find out from the nearest college or university. You can also ask local plumbers how copper pipes fare in the local soil. Speak with someone at the company whose product youÂre considering buying. Are there local installers doing DX? Ask for references  and follow-up! Perhaps your local electrical utility company has some information. You can also ask IGSHPA at Oklahoma State University for information. E-mail a question to copper.org.

More than likely, itÂs not a problem  but verify! IÂve only Âheard of it being a problem in the state of Connecticut.


    Bookmark   February 6, 2007 at 1:10AM
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Thanks, Steve. I'm on it.

More questions/problems(?). I have drainback solar DHW but the 180 gal. fiberglass tank will need replacement (ran it above 165F two summers ago). Can this system be somehow integrated with DX? Any experience with DIY built horizontal tanks (lumber/plywood/cement board?) with a custom EPDM liner?

Mother-in-law (92) lives with us and requires her two rooms to be warmer. How does DX go about providing a dual zone system? Duct warmers? Dual heat pumps? Are there reasons to install, say, a 4-ton and 2-ton vs. one 6-ton unit? Does it make much difference if heat is the major concern and cooling relatively minor? (We currently have three small window A/C units that are run sparingly.)

When I built the house in 1985, I installed an insulated heatsink(4'sand/plenum/400'of 4"corregated black drain pipe) beneath south half of the house: keps the walkout floors warm and keeps the house from overheating in the winter. LOTS of due south glazing. Can I keep the heatsink with DX? Our 2600 sf house has the footprint of a smaller house but with a double depth garage , it just LOOKS big.

My "consultant" came out. looked, took some pictures and measurements, but has been somewhat tardy in supplying my house analysis (it IS complicated). Would it be a good idea for me to run Hot2000 and do my own study, or would I be intruding on a professional and bruising feelings?

The closest Nordic distributer is over 150 miles away. Do these guys travel that far to perform their magic? If not, am I stuck with a different system that may be suggested (eventually?) by my consultant? Options?

I'm inclined towards DIY, except I can't do the drilling (vertical is the only option). I can do plumbing, but HVAC stuff I leave to the pros. Is there anything I CAN do to reduce costs?

Best location for holes is in the drive/parking area. This will require horizontal drilling about 50' under the garage slabs from the manifolds to the furnace room, crossing 2' below the water pipe from the well. How expensive (per foot?) is horizontal drilling? What is the obligatory distance from my well? Does this appply to the horizontal well runs too?

Sorry if all these questions are inappropriate for this forum. I'm early into the process, impatient with my "consultant" (I'm his first REAL client out of the previous 23 he has dealt with) and want to put in a solid system, one that will outlast me (I'm 75) and perform splendidly for years. While cost is certainly a factor, enviromental responsibility ranks higher. I will not go ahead with this product without hiring a design engineer, so questions posted here are only to aid in my education of what can be done and how best to do it. Thanks for any help. I'm encouraged to see that you monitor the forum closely.

Bob in Newport, MN

    Bookmark   February 6, 2007 at 1:32PM
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Re: bobdove

The first thing I would recommend would be to have a professional do a Manual-J and Manual-D analysis of your home and its requirements to be properly heated and cooled by a heat pump. The results and requirements will be the same irrespective of what type of HP you select. THEN select the HP or HPs. This is NOT a DIY project!

The DX GSHP will work like any other (air-source) HP but with a few important exceptions. There is no outside unit and the efficiency of the GSHP does not change with changes in ambient outdoor temperature. Only a GSHPÂs efficiency is constant. That means that when (if) it cannot keep up with the heat losses the back-up AUX heat strips come on only to ASSIST the HP as opposed to INSTEAD of the HP, as with an air-source HP.

If you need lots of hot water, beyond what a desuperheater can supply, choose a DX Triple Function GSHP.

ItÂs usually best to do the drilling in the front of your property. Let your contactor figure out how best to get all the pipes into the mechanical room. YouÂd be surprised how easily Âmajor problems can sometimes be overcome!


I have one question that I always throw in when asking someone about their ÂprojectÂ, any project. ItÂs always my very last question and it comes after theyÂve loosened up a bit. The question is, "If you were to do this same project over again, what would you do differently?" I usually learn more from this one question than what IÂve learnt from all my preceding questions combined!

Based on my own personal experience with owning a Nordic-DX GSHP, if I had to do it again, IÂd pay ANY premium to get those guys out here again and install the same damn thing!

Good Luck,


    Bookmark   February 7, 2007 at 2:10AM
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Since this thread has been revived I figured I would update you on my progress. I contacted Nordic and they wont sell a DX to just any contractor. They say only to extremely experienced installers that they have a long standing relationship with. I did however find a dealer who would sell me one but I dont want to do anything until I find out how "difficult" it is to install. I thought one of the main selling points of this unit was the ease of installation. Do you know of anything about the install that would go beyond the realm of any competent HVAC contractor? Other than the drilling of course which BTW I have a long time water well driller who has done some geo loops to do the drilling. I dont know if you are an HVAC guy or not but if you saw the installation of your unit maybe you saw something that could help me out.

    Bookmark   February 9, 2007 at 10:17AM
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Re: fabmaster

I think carefully done it should be just fine. The copper lines have to be properly silver soldered with dry nitrogen bled through the system. ItÂs preferable to pressure pretest the copper tubing before installation in the boreholes and to properly vacuum the system. Personally, I think there is more to go wrong installing a liquid GSHP system.

Proper grouting of the boreholes is also essential for optimal thermal conductivity and to prevent contamination of ground water, among other reasons; but thatÂs the case with any vertical bore field. I have not heard of ph being a problem in Texas, so I think youÂre OK there  but donÂt take my word on it DO YOUR HOMEWORK!

If your having difficulty finding a dealer to provide you with the HP you may want to send me an e-mail though this site for some help and ideas. Title it GEOTHERMAL.

Good luck,


    Bookmark   February 9, 2007 at 10:00PM
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