I'm ready to replace an old inefficient 5 ton heat pump and would like to go geothermal. The location is very rural with plenty of room and nearby ponds. I have a cousin in the A/C business but without geothermal experience and I am, among other things, a heavy equipment contractor with an excavator capable of digging 18'deep.

The soil type is 'Orangeburg B' with red sandy clay loam subsoil, 40-65% passing a #200 sieve, basically Deep South red clay! Also, within 130 yards of the site is some very hydric soil with water on the surface much of the year. There are a number of ponds from 2 to 15 acres area on the property but they are even further away. Both the hydric soil and ponds are around 30' lower in elevation.

Initial research into this with a geothermal contractor was discouraging, he indicated a very large and deep well was the only way to go, the whole thing about 10 times what it would cost to just replace the conventional heat pump,  basically he did his best to make this all as complicated as it could be which always raises a red flag for me... Further research with my local electric cooperative was not much more encouraging, I was told ground loops do not work and the expense of well drilling and geothermal in general will generally not pay off over time vs. a high efficiency conventional heat pump! I suspect both have an agenda so I need more info...

1) How is thermal conductivity of soil determined in ground loop designs? Has someone been kind enough to do this work, where are they and what does their knowledge cost? Is this expressed in BTU/hour/length? It seems a fine soil like this red clay would be ideal for a ground loop...

2) What are the practical limits to the length of these loops? If this clay isn't efficient at conducting heat can more and more pipe be used either as a ground loop or to reach the hydric area or ponds? Does this depend on the make of poly pipe friction coefficient or is something else at play here, does the pipe just become too expensive?  What about using PVC (I know, gasp!) to move the working fluid to the heat exchanger location and then using HDP or the 'Slim Jim' device? Is seems like some geothermal heat pumps need an external pump for loops, what about just using a higher pressure pump to make up for loss of head?

Thanks for any input, I've searched but haven't found what I needed. I fully realize some of you will tell me I just need to write a big check to geothermal contractor, that this is what they get paid so well for, etc. but I'd have to ask those people how many times they've rented a backhoe instead of writing the big check to the excavation contractor, LOL!!!

I have to laugh at people who say that ground loops don't work.  I have a 3400 sqft house that is heated entirely with a geothermal heat pump.  The last few weeks we have had  outside low temps of 10 to 15° F with highs in the 20s.  I keep my inside set at 72°.  The heat pump does not struggle to keep my house warm.  My ground loop consists of 5 slinky loops each with 1200' of pipe.  My total excavation was 600' of trench 1' wide by 9' deep.  My  soil is a brown clay.  My heating bill for all of last winter was $161.  For the whole year, not just one month.

Any body who tells you geothermal doesn't work or the payback is forever is either uninformed or lying.

My case is not unusal,  there are thousands of others just like mine.

Attached is a chart showing conductivity of different soil types.

You can contact me through my website listed below.  I will help you design a loop for your project.

Thanks for the info, I knew I wasn't getting the whole story!! I need to get cousin to calculate tonnage/size for the building with whatever software is used now, I understand a lot has changed from the 'rules of thumb' and a piece of paper 14-15 years ago when he installed the existing 5 ton... That and the addition of insulation, insulated doors and windows may indicate something in the 4 ton range, especially to run long enough for efficiency and to deal with the humidity we have down here given the 2,100 sq ft space on the 1st floor. With that we should be able to move forward with choosing a particluar heat pump and then designing an appropriate loop...

abh3,

you really should look at a DX geothermal system. It would be a great fit for your setup. Just do a horizontal loop. Geodean should be able to help you with that design, too.

What about corrosion? The subsoil we have is seriously acid, I've seen galvanized pipe pretty well eaten up at some rent houses I was rehabbing, though that did take 30 years to happen!! Does DX rely on coatings or sacrificial anodes, like a boat, to keep all those electrons where they are supposed to be? Given how expensive just regular soft copper tube is now, would a copper groundloop make economic sense or is it that much smaller and more efficient than HDPE?

No. If the soil acidity (pH) is lower than 6.0, then you simply have the corrosion protection system by EarthLinked installed. This is an impressed current cathodic protection, NOT a sacrificial anode cathodic protection. It constantly bombards the copper loop with electrons to replace those being eaten by any acid in the soil.

As far as efficiency, EarthLinked units range from 15% to 40% more efficient (higher COPs) than typical closed loop HDPE systems. Also, because the ground loop is already engineered, there's no guesswork on it. It also takes a smaller footprint. As far as installation costs, I've seen it be about the same as the HDPE systems to significantly less than the HDPE systems. That all depends on a whole lot of variables...

Anyway, EarthLinked DX will give you higher efficiencies, less loop maintenance, and will give you a very long life on the loop and equipment. Just take a small soil sample to the NRCS for a pH test. It shouldn't cost anything. Are you near coastal waters or brackish (salty) marshes, or are there known sulfides/sulfates in the soil?

The subsoil PH is in the 4.5-5.5 range according to the USDA/SCS Soil Survey, I've never had an actual soil test done on dirt that deep but tests of topsoil suggest they aren't far off the mark, usually requiring 2-3 tons of dolomitic lime per acre of 'new ground' in agricultural applications. We're 50 miles from the Gulf so salt isn't a problem, I'm not sure about sulfides/sulfates...

I guess I need to consider DX as well and compare initial costs and operating costs to closed loop poly. Unfortunately, I'm having a tough time finding specifics, the American Geothermal site links to a pretty vauge earthsource-energy.com, ECRtech.com has a good FAQ section, geoenergyusa.com is pushing their 'geocolumn', earthtoair.com sells efficiency & low excavation costs but there isn't much about specific model specs, part numbers, etc... The makers of the water type heatpumps tend to have technical details online to help with, for instance, deciding if a paricular unit can physically fit where my old horizontal air handler is now or whether this turns into some remodeling of the house for some left-hand vertical unit, etc. adding to the inital cost.

Also, are these DX units available through the usual HVAC wholesale distrubutors, like my cousin deals with? I fear a manufacurer's dealer won't work with another HVAC guy and will insist any excavation be done by HIS man, etc. which will really negate my advantages here...

Thanks!

You should be able to use your cousin. He just needs to be trained and certified to do the system. EarthLinked has many trainings available. On their website, look under News, Training.

As far as fitting the system in the house, the heat pump is its own unit, and the air handler is separate. It's a split system--at least it is with the EarthLinked (ecrtech.com) system.

For your pH, you'll just need the CPS (corrosion protection system) impressed current cathodic protection.

Where are you located? I'm the sales rep in Utah. I'm sure the sales rep for your area would be glad to get another dealer. If not, let me know. It will save you a fair amount to do your own excavation.

If you have more questions on EarthLinked systems, let me know.
Keep us posted.

Is it possible to add lime or something else to the dirt when you back fill the trenches to help neutralize or reduce the affects of the Acidic soil? Would this solution work over the long run, or would this be a tempory fix at best?

Since you are so close to the Gulf take a look at http://www.centralcityair.com/. There's some missing pages there and I don't know how up to date it all is since the guru of the site and company died 2 years ago. But there's a lot of info there about considerations in sizing AC systems for the Gulf climate, particularly why you should undersize the evaporator for humidity removal. If you use a 4 ton system you will probably want to use a 3 or 3 1/2 ton evaporator. I used to live in Louisiana and when I replaced my conventional AC unit I went with a 3 ton condenser and a 2 1/2 ton evaporator. Worked great!

If you live anywhere near Baton Rouge send me a message via the "Message" button on the left and I'll send you the name of a guy I used to work with who put in a Water Furnace system in his new home about 4 years ago.

I know one of the sales reps in indiana usually puts crushed lime in the horizontal loops for that reason. I don't know if it's a permanent fix or not. He still uses the CPS.

On humidity removal, EarthLinked's refrigerant controls make it so that humidity starts to be removed within the first minute of operation. It's a wonderful design.