I just looked up my well driller on the IGSHPA website and he is listed as an Accredited Installer.

Here is some more info on heat exchange borehole filling/grouting:

785:35-7-1.1. Minimum standards for construction of heat exchange wells

Excerpts from the above link:

(c) Construction standards for vertical closed-loop exchange wells. Vertical closed-loop heat exchange wells shall be constructed in accordance with this subsection. Site specific conditions shall be assessed to determine the best method and materials to be used for sealing and filling the well annulus to protect the groundwater. In addition, but not as an alternative, to the requirements stated in (1) through (9) of this subsection, methods and materials for construction of heat exchange wells that meet or exceed recommendations specified in "Grouting for Vertical Geothermal Heat Pump Systems Engineering Design and Field Procedures Manual", International Ground Source Heat Pump Association, Oklahoma State University, First Ed. 2000, and in "Grouting Procedures for Ground Source Heat Pump Systems", International Ground Source Heat Pump Association, Oklahoma State University, 1991, may be used for construction of vertical closed-loop heat exchange wells.

(7) Vertical heat exchange well sealing and filling materials and methods. The well annulus must be completely sealed or filled the total length of the borehole with approved materials and methods as listed below.

(A) A bentonite, cementitious, or Portland cement grout seal shall be installed from a point thirty (30) feet below land surface up to the excavation trench that connects the closed loop to the heat exchange system. Spreading or expanding clips shall not be used within the top thirty (30) feet of the borehole.

(B) Approved annulus sealing and filling materials below thirty (30) feet shall include Portland cement, high solids bentonite grout (20-30% solids by weight),bentonite pellets or chips, water well filter pack sand or gravel, or approved high efficiency or thermally enhanced grouts designed for geothermal borehole.

(F) When non-slurry sealing and filling materials are used, only clean water well filter pack sand or gravel or chipped or pelletized sodium bentonite varieties that are designed to fall through standing water are acceptable when sealing the annulus of a well that is below the water level in the saturated zone. The borehole shall be flushed clean of all drilling mud and debris left over from the drilling operation so that the bentonite products designed for this type of installation will gravity feed without obstruction. Material shall be introduced in a manner to prevent bridging of the materials in the borehole annulus. A measuring device such as a tagline shall be used to measure and document placement of the materials installed.

If I go with the coarse sand backfill as discussed previously, my 5' iron pipe on the 3/8" nylon rope will be the tagline / measuring device to insure the sand is not bridging and the hole is filled.  A 5 gallon bucket of sand should result in ~6.5 linear ft of borehole fill.

Since I'm on well water, would it be a good idea to use an indirectly heated water heater tank with separate heat exchange coil for my geo pre-heat tank? My concern is the well water circulating through the hot water generating coil on the geothermal unit. My well water is very hard but I run it through a water softener and I generally don't notice any scaling problems. With an indirectly heated tank, I could use purified water for the hot water generator loop. Are there any disadvantages to this approach other than the cost of the tank? I've located an indirectly heated storage tank with stainless steel tank and stainless steel heat exchanger coil for ~$150 more cost than a comparable sized standard electric hot water tank. I'm willing to spend the $150 extra if it means fewer problems down the road. I assume I will have to install a small expansion tank on the hot water generator loop since it will be a small closed loop.

the issue with cement based grouts are that fact that they are rigid. HDPE pipe expands and contracts with the heating and cooling cycle. This should concern you.

There are people commenting on this thread who install loops day in and day out, and others who have never installed a loop.

You should read this before you jump to any conclusions: IGSHPA’s ‘Grouting for Vertical Geothermal Heat Pump Systems, Engineering Design and Field Procedures Manual’

"Since I'm on well water, would it be a good idea to use an indirectly heated water heater tank with separate heat exchange coil for my geo pre-heat tank?"

No

Here is some more info on heat exchange borehole filling/grouting:

785:35-7-1.1.

You should probably point out that the above is an Oklahoma state specific document that doesn't regulate elsewhere. Check your specific state and county for more restrictive requirements or recommendations.

So, if the water isn't moving at all (or not quickly enough to strip off the external
surface boundary layer), thermally enhanced grout will be several times better
than water

Put a pan of wet sand (the grout being discussed) and a pan of water on a stove and you will learn otherwise.

IGHSPA is located at Oklahoma State University. All of their online documents will say Oklahoma.

Posted By jonr on 11 Apr 2015 09:48 AM
Put a pan of wet sand (the grout being discussed) and a pan of water on a stove
and you will learn otherwise.

The wonderful thing about science and engineering is that we no longer
need to personally repeat every test and measurement that's been made
by fellow techies since the mid 15th century. H/T Johannes Gutenberg.

Material ................. W/m-K
saturated sand ...... 2.0 to 4.0
moist sand ............ 2.1 to 2.3
sandstone ............. 1.8 to 3.9
liquid water ........... 0.6

Posted By jonr on 11 Apr 2015 08:56 AM

Here is some more info on heat exchange borehole filling/grouting:

785:35-7-1.1.

You should probably point out that the above is an Oklahoma specific document that doesn't regulate elsewhere. Check your specific state and county for more restrictive requirements or recommendations.

That is true.  Those state regulations apply only to Oklahoma.  But Oklahoma State University is also the home of the International Ground Source Heat Pump Association (IGSHPA) frequently mentioned in this thread.

http://www.igshpa.okstate.edu/

Also, a large part of eastern Oklahoma and western Arkansas is within the Western Interior Plains Confining System which is what I am dealing with at my site where the thickness of the system exceeds 6000 feet per the following map:

http://pubs.usgs.gov/ha/711h/plate-2.pdf

Posted By joe.ami on 11 Apr 2015 08:55 AM
"Since I'm on well water, would it be a good idea to use an indirectly heated water heater tank with separate heat exchange coil for my geo pre-heat tank?"

No

Can you explain why?

Material ................. W/m-K
saturated sand ...... 2.0 to 4.0
moist sand ............ 2.1 to 2.3
liquid water ........... 0.6

If convection didn't exist, it would be that simple.

Summary of the well done science/engineering/measurement here: use no grout if the borehole will be full of water and you don't need hydraulic sealing.

Posted By jonr on 12 Apr 2015 10:00 AM
If convection didn't exist, it would be that simple.

Unlike a pan boiling on the stovetop, a vertical loop
has much smaller delta-T, and thus a smaller density
gradient. Worse yet, the density gradient is in the
wrong direction, i.e., it's perpendicular to gravity,
(rather than parallel to it as with the pan-on-stove
experiment).

If you're willing to spec a loop based on the stovetop
convection model, you're a far braver engineer than I.

If you wished to isolate your DSH then you would have to set it up as a boiler with expansion tank, pressure relief and make up water as well as the higher buffer cost.....cost v benefit.

Posted By joe.ami on 12 Apr 2015 11:23 AM
If you wished to isolate your DSH then you would have to set it up as a boiler with expansion tank, pressure relief and make up water as well as the higher buffer cost.....cost v benefit.

Thanks.  I did forget to consider the pressure relief valve; although, the cost for one is only ~$20.  For makeup, I could just install a valved supply from my water supply line.  There shouldn't be much if any makup required after initial loop fill assuming no leaks.  This would also assure the loop remains filled and pressurized.  I'm still on the fence regarding the isolated DSH loop, especially if I can get the stainless buffer tank near the same cost as a standard electric water heater.  The standard un-powered electric water heater tank for the buffer tank would definitely be simpler and less costly overall.  If I go with the standard electric water heater, I could install isolation valves and fittings in the line to allow mild acid flushing of the DSH coil if necessary in the future and the anode rod in the electric water heater tank would provide some level of corrosion protection of the DSH heat exchanger.

You asked for an opinion, personally I think you are reinventing the wheel. You can get a 50 gallon elec tank for south of $250. I don't know how you are going to come close with anything else pricewise.

Posted By jonr on 12 Apr 2015 10:00 AM

Material ................. W/m-K
saturated sand ...... 2.0 to 4.0
moist sand ............ 2.1 to 2.3
liquid water ........... 0.6

If convection didn't exist, it would be that simple.

Summary of the well done science/engineering/measurement here: use no grout if the borehole will be full of water and you don't need hydraulic sealing.

You should not just cite scientific papers and take sound bites out of them to support your point when they actually do not. The conclusion you are citing comes from a computational model in a 10 ft borehole without any cracks in the surrounding rock, pretty useless for real applications. In the real world, your pipes are all over the borehole, not at a steady distance from the wall, you are making ice or you melt ice (phase change), you have convection or you don't have convection.

Posted By joe.ami on 17 Apr 2015 10:50 AM
You asked for an opinion, personally I think you are reinventing the wheel. You can get a 50 gallon elec tank for south of $250. I don't know how you are going to come close with anything else pricewise.

Being an engineer, I do sometimes tend to over think things.  And working in the nuclear power industry for over 25 years, I tend to overbuild things and want to have redundancy, backups, and contingencies built into my designs.

Anyway, the least expensive 50 gallon electric water heater that I can find locally is $310 + tax and an 80 gallon model is $580 + tax.  Online I have located a 75 gallon indirect water heater with stainless tank and dual stainless heating coils for $600 + $100 shipping.  For the indirect water heater approach I would need to add another $50 or so for expansion tank and pressure relief valve. 

Another idea for considering the larger buffer tank was that down here with 63F deep earth temp, the limiting factor on my loop design is heat rejection in the summer and having a larger hot water buffer tank would keep more BTUs in my hot water storage tank rather than putting it in the ground.  Raising the temperature of a 75 gallon buffer tank vs. 50 gallon buffer tank by ~50 deg F results in an additional 10,000 BTU put into my hot water storage tank vs. the ground.

At this point I'm probably leaning towards the basic 50 gallon electric water heater for the lower initial cost and simplicity, but I was just wanting to bounce some ideas off the more experienced on here.  Thanks for all of the input.

The conclusion you are citing comes from a computational model in a 10 ft borehole without any cracks in the surrounding rock, pretty useless for real applications.

Of course it discusses cracks: "The groundwater will flow into these fractures, thereby increasing the heat transfer even further." And it extends the analysis to greater depths (this also increases convection and heat transfer). And it did some analysis of variations in distance to the borehole wall.

If you prefer real-world experience, there is "In Scandinavia, boreholes are usually not grouted but left with groundwater...".

It also says "This makes water an inexpensive and competitive filling material in borehole heat exchangers compared to other commercial back-filling materials, with regards on heat transfer properties.". Let's us know when you have any borehole measurements (or do PhD research) that shows otherwise.

Ice might be a factor, but then it's a good thermal conductor.

Just an update to this thread. I had my geothermal wells drilled over the past couple of days. Everything went according to plan, mostly. The driller went down to ~240', so now all of my loops are short of my basement wall by a ~5'-10' so I will have to fuse some extensions on the loops pipes to get them to my header in the basement. But, the extra 10' of borehole should improve performance. I taped two (2) 10'x1/2" pieces of rebar to the loop U-bends and filled the loops with water using my adapter for filling tractor tires with water. The driller had a hose reel that sat on the ground and we used that to spool the pipe into the hole. No issues whatsoever. Pipe went to the bottom of the hole with little effort. The holes were filled with water to within ~15'-20' of the surface. As expected, he drilled through 30'-35' of hard red clay, then hit black shale the remainder. We hit water at 40'-45' that was producing ~5-10 gpm water. No change in water production was noted through the remainder of the drilling. After the loops were dropped into the holes, I dropped my 5' iron pipe on tag line down the hole then began back filling with course sand and pulling the tag line out as I filled. No issues. I filled to within ~30' of the surface and am letting it settle overnight before back filling the remainder with bentonite pellets.

The driller averaged ~3 hours per hole including truck setup until the loops were in the hole. It appeared to me to be fairly easy drilling.

Cost of the well drilling went up from my initial quote. The price was $7/ft, but I was charged based on my requested 230' of depth rather than the actual ~240' depth. $4830 for three (3) wells 240' deep plus ~$150 for fill sand plus ~$300 for bentonite pellets plus ~$500 for 3 loops of 3/4" x 510' HDPE pipe. I will have to buy a 100' roll of 3/4" HDPE pipe and some socket fusion couplings to finish the loops. I will also have to rent a trencher for ~$150/day to dig the trenches from the geothermal wells to the basement wall penetrations.

Since I first started this thread, I have completed installation of all of my ductwork. This includes my supply plenum and zone dampers. All ductwork is round metal, insulated, and located in the open web trusses between my main floor and basement. That was a chore that I'm glade is finished.

Next on the agenda is to order my unit and hot water heaters, set them, connect the unit outlet to the plenum, build my loop header, and connect all of the plumbing.