We will be building a home in eastern Tennessee.  The area is heating dependant on the Cumberland Plateau.  I would like to use a geothermal heat pump for heating and cooling needs.  However, our building lot has some significant limitations, the first being the depth to bedrock averages about 42” across the lot.  I do not believe that the ground freezes, so there is not a freeze line to worry about.   I have ask a couple of well drillers in the area about drilling bore holes and all have said that they had drilled boreholes in the past for geothermal systems, but would not give me any idea regarding prices for drilling bedrock.

 
While I know that there are a lot of variables involved in the construction, we are planning to use SIP’s for the walls and roof.  The topography may allow for a walk-out basement which will have 6” to 8” poured walls on an insulated slab. 

My questions are as follows:

1.         Is it feasible to drill through the bedrock?  I assume that I will need several holes for the vertical loop.

2.         Based on the approximate size of the home (approx 64,000 cf of conditioned area) and garage (18,000 cf of partially conditioned area) what number of bore holes would be needed?

3.         While I know that every job is different, what is the typical cost per foot of drilling the bore holes?

4.         Is the depth to a water table critical for geothermal, as I plan to use a closed loop system.

I would contact TEI Rock Drills if I were you. They have great little rock drills for your situation. Ask them if they have one in your area. I'm pretty sure they have an office in Tennessee, too.

Yes, it's very feasible to drill rock.

The tonnage could vary greatly based on number of windows, too. I'd guess anywhere from 5 to 10 tons. Obviously, a guess won't cut it. You need an accurate load calc.

Cost per foot varies greatly, too. I typically charge $10 per foot for the 100' x 4" boreholes of an EarthLinked DX system. If it's for water source, it depends on what I'm drilling through, but I range from $12/ft. to $24/ft.

Water table is not an issue with closed loop EarthLinked DX.

Clark,

I looked up TEI Rock Drillers. They have sales facilities in Little Rock, AR and Asheville, NC. The Asheville location i about two hours away. I will email them to see if that have drilling contractors in my area. Is there a specific drill rig that I should ask about?

As part of the SIP design, I am getting the HVAC system engineered as part of the package. That should get me sized properly. I know that windows are like big holes in the house. However, to minimize the energy loss, I plan to invest in high efficiency units. I am looking at fiberglass frame units, but will reassess my design as the build date gets closer. Hopefully fiberglass units will come a little more in line with vinyl.

Having no experience with geothermal systems, I do not know much about them, other than they are very efficient. If I recall an EarthLinked DX system consists of direct burial of the copper loops in a thermal transfer grout. What considerations need to be made regarding the corrosive nature of the soil and bedrock and what is the typical life expectancy of the loop? Thanks for the information so far!

The pH of the soil needs to be tested. If it is higher than 6.0, it needs no corrosion protection, and will NOT corrode. If it's below 6.0, you'll just need a CPS, impressed current cathodic protection system. It's available through EarthLinked. This will ensure at least 50 years on the copper, if not more.

If the CPS is not needed, the copper will never corrode, and that won't ever become an issue for you.

For the drill rig, you'd just need one that can drill at least a 2.5" diameter hole, 100' deep for EarthLinked. They have lots of rigs that do this in rock.