Hi! My husband and I are getting quotes for a geothermal system. We have to do vertical wells because of the amount of limestone. We are getting conflicting stories from the contractors regarding the use of grout in the wells. It is not required in the state of Kentucky. Two contractors are saying because of all the limestone which is the best conductor, it is not needed and the grout would actually decrease conductivity requiring the wells to be longer. Another contractor said we should absolutely have it to insure contact all along the well because you cannot be sure where the air gaps are. He said the grout allows his wells to be a shorter than if he did not grout. Who do we believe? This is a big investment and we want this done right. Thanks for your help! Kristi
There are only a few active drillers on this site, myself being one of them. There is a grout manufacturer who may chime in as well. I can see both of the arguments being presented to you. By NOT grouting your wells in limestone you would get excellent heat transfer through the limestone,BUT your loops are not in contact to the limestone completely and would lose performance due to air gaps and incomplete full contact to the limestone. By adding grout your wells correctly ( from the bottom up) your completing a seal, and full contact to the limestone. Your attention to details in the grout are important too. You are going to want a Thermally Enhanced grout to help match the conductivity of limestone. If a opinion either way is what your looking for..... Then my vote is to grout the boreholes with thermally enhanced grout and make sure all bidders are on the same page. -Dan
What Dan said. I will also add that the secondary function of the grout has nothing to do with the loop. It creates a non permeable seal in the bore hole to protect the enviroment/ groundwater from any potential source points of contamination. Although grout is not required in all areas, IGSHPA promotes it. I also find drillers who choose not to grout, whether it is required or not are poor stewards of our world. When you add the notion of geothermal to that statement it creates a hypocrisy of thought. Eric
I can not believe grout is not required in nationwide for the reasons listed above. This should be industry standards everywhere.
We agree with what you all wrote and that's what we expected but were surprised when 3 of the 4 said no to the grout. We appreciate the clarification. One of the contractors who did not use grout said he expected Kentucky to start requiring it in the next few years, but he said it was not worth the expense, so why bother? Of course, none of the 3 who didn't use grout said anything about protecting the groundwater. The contractor who said he would use grout said the wells could be shorter. Another one who said he would not use grout because the wells would have to be longer. Thoughts on that? Also, you said to use a thermally enhanced grout. Can you use the limestone spoils or is it best to go with a commercial silica/sand mix? Thanks again for helping us out!
The standard is a silica sand mix to add to the grout, however it is all about location and the local talent. If the local talent mixes limestone spoils in with the grout and has a track record of happy results, then by all means go with them. The point of thermally enhanced grout is to provide protection for the enviroment, as well as promoteing thermal exchange rather than insulating the loops from the natural lithology. It is a razors edge, but both goals must be achieved to be good stewards of our world. Eric
being a driller, we always grout. I agree with Dan and Eric. You are paying the bill, you should get what you want.
I would be weary of anybody not offering grout. They either do not understand the importance of grout, or do not own a grout machine since it is "not required" in there their state. Not owning a grouter is not a excuse to say grout is not needed for performance and ground water protection.
Thanks everyone for your comments. It helped a lot! We are going with the contractor who grouts. Everything he told us through the process coincided with what you have said. We feel comfortable he is giving us the best system we could find.
One question to ask, how high is your water table? If the water is near the surface, then the pipe conducts through water, not air. Water itself isn't a good conductor, but moving/convecting may be. Thermal grouts have heat transfer ratings. But I've seen no data for water submerged vertical loopes.
Really???? David you have been here long enough to know that the loops efficency is not the only thing in play here. We have all stated what the function of grout is. Sure water is a better conductor without the grout, but.... we are stewards of the enviroment, not rapists. Eric
I ask to learn. The original poster did not state the proposed depth of the loops or the water table height in winter. Grout certainly solves any concern for the latter. It is not my intension to disrupt the forum. Actually, it is an 'engineering' question slightly vailed. The thermal conduction of water is poor ... not much better than PE itself (0.58 vs 0.5), so not an ideal 'pseudo-grout' though much better than air. Some, for example, have asked about using copper instead of PE pipe - which thermally conducts thousands of times faster. But the 1/16" pipe wall is only one factor in the system. Others have posted that in practical terms it is not necessary to have grout mixtures above 0.85 although some engineers have speced higher. I seek to learn: 1) what was asked ... the effective thermal conduction of convecting water. 2) the design specifications for a standing column verses closed vertical loop. (A question posted a long time ago) As far as protecting the ground from contamination, would not the more environmentally friendly thing be to design all systems to run with 100% pure water?
No disruption, but I would point out that for every action there is a reaction. Many geothermal ideas are fun to muse about while bending an elbow, but the enviroment and cost allways win out in the end. Eric
Is your environmental concern regarding antifreeze in the loop? Or is it the potential of outside contamination - the same as for a water well? What is the average cost to grout a well? One fellow on this forum was quoted $9 per foot. I was quoted $2000 to grout a 500' well. It is possible that grouting costs would break the deal and this couple NOT install geothermal. What is the environmental impact of continuing to heat with fossil fuel instead of a heatpump? It isn't wrong for the above couple to have all the facts. Unfortunately the initial cost of geothermal systems is so high that most simply cannot afford it. Forty percent of energy use in this country is for buildings ... with over half of that being heating/cooling. One persons balance between environment and cost is another's cutting corners. Once a law is in place, the debate is gone. But laws can cause problems as well. Quite frankly, I'd ban gasoline and diesel if I could. To protect health and environment.
A big part of grouting is to prevent cross contamination of aquifers. Geothermal drilling is not investigative drilling. It is production drilling. You are not driving split spoon samples every 5' for example. My point being, you need to be proactively careful and grout. That is, unless you spend the $10,000 to carefully delineate the stratigraphy and have a hydrogeologist make the call that there will be no aquifer mixing and a surface plug is enough. So really, just grout.
The reality is that many states are not even close to being up to speed about the possible contamination that occurs when you drill a loop throug multiple water bearing units. We must protect the water source of those citizens that are down gradient from the bores we create. Again we are stewards not rapists. The cost of grouting a well is a moving target based on depth, diameter and lithology being sealed. If you stop by geo pro inc website you can peruse the grout cost calculator and get a good idea of the cost. In many states domestic and municipal water supply well grouting is not standard. IGSHPA recognised the risk early and set standards to ensure that the geo exchange best practicies included grouting. Anything less than that is rounding a corner into a circle. Eric
