Enhanced thermal grout and thermal conductivity
Quick questions for residential install, 2400 sq ft house, 30,000 btu heat loss, Allentown, PA.
Should the contractor use thermally enhanced grout and if so, what conductivity, and should a thermal conductivity test be done? Here's what my contractor said about it:
"We use bentonite grout for our residential jobs which has a conductivity of .4, we also use if the water table is high, stone then grout which is very good. You must understand that we also in addition to doing many, many residential jobs we also do large commercial geo loop fields for schools, government buildings and institutions in 5 states. Commercially we do what is call a thermal conductivity test prior to the field install which measures the sites geologic conductivity, for residential jobs the cost would be prohibitive, that is why we have standardized to 150 foot of bore per ton. We can grout with thermally enhanced grout but there would be an additional cost for that. The true purpose for grout is to protect the water aquifers which is the first concern, in recent years the use of enhanced grout is being used to reduce drilling cost for large jobs."
So, this contractor is lowest bidder and happens to be the most experienced also. But I want to make sure they aren't taking shortcuts that will sacrifice the efficiency of my install.
We do the same exact things here in NJ.
Our average drill depth is 180'/ton with 1" loops.
We use bentonite grout for our residential jobs too. The grout is used to protect the aquifers, and also make contact with the earth itself to transfer heat.
Your contractor is correct about the price of a thermal conductivity test being unnecessary and not cost effective for small residential systems.
Your local driller will know the formations he is drills into and have a good idea of the heat transfer too.
A lot of the times a cheaper bid in geothermal drilling means the driller simplified his process and can do it much more efficiently than some other people.
For information straight from the horses mouth, contact geopro on the www. They invented thermaly enhanced grout products and their position is the same as your contractors.
In Allentown I would anticipate rock drilling? If that is the case the grout has another function other than protecting the groundwater. In rock the grout ensures the " link" between the loop and the rock in the absance of water. If the link is not made the loop will be ineffecient, and or fail.
A standard 18-20% solids content for grout is " as typical" for the lion share of resi projects.
Ok, thanks. Yes, I would think rock drilling, it's shale here.
One last thought, why don't you use thermally enhanced grout? Using grout at .8 conductivity vs .4 would make the system more efficient, save me $ on my electric bill correct? Is it another one of these trade offs you have to weigh between higher upfront cost vs lower electric bills, and the break even point is like 20 years or something?
I have found this to be quite true and is an excellent piece of advice.
Originally Posted by CallaDrilling
Thermally enhanced grout was developed to reduce the footage on commercial projects to deliver the most cost effective loop field that will carry the load. The important factor to consider is that commercial projects have all had a conductivity test done to determine the exact amount of thermal give and take for a given site. If you add thermal grout to a project with no base line data, you are dabbling in voodoo math. It costs more to handle and purchase, and no seasoned looper would ever reduce footage based on voodoo math, so it really is a point of diminishing return without the upfront data. For resi-geo the mantra is and should be " k.i.s.s. ".
Originally Posted by gregbig2
I have seen thermal grout on residential projects touted as a sales gimmick, but without upfront data to compare the back end results to, it is just a big guess.
Ok, got it. That makes sense. Thanks again.