A local installer said that if water is always at the top of a vertical column, then grout is not needed and that grout reduces performance. However, I read that grout is used to prevent contamination of aquifer. And that thermal grout has twice the thermal conductivity as water (1-1.2 vs 0.58). The latter seems surprising, given water's capacity to store heat. Any thoughts? Has anyone ever seen or heard of an ungrouted vertical loop? Perhaps shared with a well (but pump replacement would be a pain)? This topic raises interesting questions: http://www.geoexchange.org/forum/ge...silica-sand-and-thermally-enhanced-grout.html This quote in particular "It is important to note hear that .88 is double the standard of around .40-45". Does this mean that non-enhanced grouts are this low number - which is well below water? In theme of my header spacing thread (2' vs 50'), given the slow rate of heat transfer in the ground, is thermal grouting a bit over touted? http://www.geoexchange.org/forum/ve...ops/5207-pipe-spacing-from-vertical-loop.html Lastly, was told shale is excellent for geothermal. Yet according to charts found, it is among the poorest. For example: http://www.gly.uga.edu/railsback/PGSG/ThermalCond&Geothermal01.pdf These 'doubts' are a concern that being told 150' vertical bore / ton is good ... now sounds like in would be inadequate.
Grout and its application is a whole nother feild of study. Akin to fusion in its complexity. I have written a paper with accompnying video to be published soon. In the mean time stop by geopro.com. It will either help you or tangle your noodle up worse. Eric
It will either help you or tangle your noodle up worse. Yes, just glancing at the home page, reading they provide "services to the Oil and Gas Industry and to Government" just blew the noodle to pieces So much info is troubling. For example, there is a Soil Thermal Conductivity table that pops up all over the place (presumably this shows how smart the presenter is) Here is an example of it: Geothermal Home Heating And Cooling - Thermal Systems Third table from the subheading "Specific Heat/Thermal Conductivity of the Soil". Reading this chart, one would need TC nearly 2.0 to get enough heat from a 150' vertical bore. More typically, one would need over 300'. Or am I reading this incorrectly ... that Depth of U-Tubes needs to be divided by 2? Definately time to go clean the chicken coop !...
This particular question interests me and I have tried to find data of someones testing. I am not convinced that grouted well will out perform a water well (assuming the water well is always full). The types of grout used do indeed have a much better thermal conductivity over water. In my thinking however, since the grout is solid the heat has to dissipate through the solid material from one molecule to the next. With water in the well there would be a small amount of circulation that could provide an added benefit to carry heat way or to the HDPE pipe in a way that grout simply will not do. How significant this benefit is I have no idea. I did find one project that tested two horizontal closed bores using the directional drilling rig. One borehole was grouted, the other was not. The ground was expected to be wet year round. The un-grouted bore actually out performed the grouted bore. I have yet to find data on a similar experiment using vertical closed loops. Another factor is state regulations. Many state require grouting to prevent aquafirs from mixing. For deep wells (region dependent but about >300') grout would likely be needed just for this reason. Another concern I have with not grouting a bore is the type of antifreeze used. Most are very toxic. A leak will contaminate your water supply and potentially be fatal. Not something to "wing it" on. Propylene Glycol is a food grade antifreeze that would probably be safer, but it is less effective than the others for various reasons. A grouted well would be less prone to leaks and contamination of ground water.
DN, the heat flux of importance is between the borehole and the earth. I'm differentiating from the heat flux between the pipe and water or grout. It's the entire borehole construction with the earth that matters. Water has poorer thermal conductivity than grout as noted. Carrying the heat "away" from the pipe serves no purpose if the heat can't be dumped into the surrounding earth.
First of all it is illegal in most states to have a bore hole that is not sealed generally with grout I have been licensed in 7 states in the midwest. In most of them you are required to seal a horizontal hole as well. Back to the issue of thermal conductivity yes grout enhances thermal transfer but the amount of sand of in the soil that the water is in can also inversely affect the ability of the well to dissapate heat. In the areas where I have drilled we have used 200 feet of well, with 400 feet of pipe, in a grouted well with a thermal conuctivity of .88 or higher, sometime graphite enhanced, per ton of load. I have drilled and completed systems in NE,SD,IA,OK,KS,MO,WY, as wells as Canada & Cayman Islands. 40 years of well drilling IGSHPA certified in 2/94 I hope this was helpful
150' per ton might be more then enough, might not be enough to keep your loop temp above 30F in the, which is not that catastrophic either. Don't
I have a water well in my bore hole basin so I know from drilling that well that I have between 15' and 17' of overburden and a static water table of 5' - 7" (67"). I had similar thoughts about not having to grout the bore holes, just use a pit-less, adapter like they use in cold climates, to prevent contamination of the aquifer and finish the well. My HVAC contractor faught that idea so I wrote to the IGSHPA for another opinion. The then director (I don't remember his name and cnnot find the email) replied that that was the method they tried when intially testing GSHP and the problem was that you have no control over the static water level in the future. And that is why they developed the bentonite grout backfill proceedure. I took thier advice and did the job right, we backfilled the bore holes.
