Hi there, I have 2 drilling quotes in front of me for 900 feet (3x300) of bore hole. The difference between the two is that one driller is using 20% bentonite grout (around 0.43 thermal conductivity) and the other is using an "enhanced" grout with a conductivity of 0.88. The ground in my area has a conductivity of around 1.4. Is there going to be a significant difference in system performance with the 2 different grouts? I'm baffled. thanks!
I would still be calling drillers looking for someone who uses a 80% mix 1.2 btu/ft The difference will be substantial
Hi and welcome, This should be entertaining. The differances in the conductivity of the grout having a real world impact on the performance of your loops is a topic for strong opinions and some times abusive language. The proof is there mathmatically and in end result case studies that using a high solids grout enhanced with silica sand equals a higher rate of conductivity. That being said the argument you will here is that if you use a high solids grout you can reduce the number of bores and or the footage of the bores and get the same results as more bores and longer bores. This is where it gets wonky. The number one cause of dissapointment with a gshx is the infamous short loop scenario or a mistake on the manual J. You will not find very many gshx contractors willing to put there reputation on the line for their reputation based on the use of an enhanced product on a residential job. The point being what is your real pay back on this grout and how super efficient is really when to say enough? If both contractors came up with the the same 2 bores to handle your load and the pricing is the same and you are comfortable with both of them, it is really a wash either way. In a rock bore the critical factor with the install is that the entire bore is grouted from the bottom to the top with no voids to steal contact with the rock, ie exchange. If both contractors are going to perform in that respect, getting hung up on the btu's of exchange of the grout is inconsequential, nature will take of that. I hope this helps, and if the proponents of grout that is enhanced to the n'th degree chime in you are in for some real entertainment!
This might help -- especially pages 7-11: http://www.mcquayservice.com/mcquay...ems/AppGuide/AG_31-008_Geothermal_021607b.pdf My (non-professional) interpretation of Tables #1 & #2 is that it's useful to select a grout with roughly same (or slightly better) conductivity than the surrounding soil, but there's little/no advantage to going beyond that. BTW, Table #1 has some interesting implications regarding the effect of flow turbulence on heat exchange efficiency -- directly contrary to the opinion expressed by a well-known itinerant "net.expert."
I'm way more interested in their references than their grout. It is the salesperson's focus and shouldn't be yours. You won't get baffled if you don't let yourself get caught up in minutae. Good Luck, Joe
Wow Looby that link made my eyes bleed! lol. I read a lot of it and the thing that stood out to me vs. other install manuals was the mention several times that these were guide lines " not for commercial". That gives the reader a more clear understanding that there are differances from residential.
