Hi fellow Geoexchange enthusiasts, I'd like to know your experiences with pipe spacers used to increase thermal exchange rate in vertical boreholes. They can reduce the total depth/number of boreholes by 10-20%, but most pipe spacers are a real pain to install. Have any of you heard of them/used them? Thanks!
The data I have seen is 8% improvement. They are a pain to install, drillers hate them, and gladly drill 8% deeper....check grout and pipe size, there might be better ways to get 8% better performance.
You would get 7-8% on low conductivity ground, like soil. But for high conductivity (rocks), software like GLD show improvement of up to 20%. The main problem remains that's it's a nightmare to install. What if there actually was a pipe spacer that's easy to install?
It is commonly accepted that when you drill in rock, a stable hole if you will, you can and should do everything and anything in that hole, including clips, multiple loops, magic beans etc. Drilling mud rotary in unstable formations, the name of the game is in and out without any complications. Using a hole loader to drag the loop down the hole does not lend itself to installing clips. Typically we drill 200' in and out with loop and grout in about 45 minutes. Nothing to gain from the clips IMHO. There is a time and place for everything, and clips in mud rotary is not one of them. Also a lot of things look good on paper or in the software but just do not stand up in the field. The whole Rehau thing comes to mind. The video that was taken off the web of the loop going down the hole over a roller in a rock bore and ejecting the clips like a machine gun also comes to mind. In the end geo is about feet of pipe in the ground the cheapest way you can get it in the ground. In my operating area a lot of push was made for thermally enhanced grout. Without a conductivity test, the application of thermal grout willy nilly is pissing in the wind. Then the application of thermal grout that exceeded the grounds thermal conductivity was another example of software applied willy nilly at a diminishing ROI that was paid for to no end. Hope this helps Eric
There are quite some things coming into consideration here. First, line heat transfer simulated by GLD assumes that the base case, pipes in the center of the borehole, or somewhere between the center and the wall. In reality, the pipes without clips are all over the borehole, and to a good degree already on the outside wall. Second, with increasing grout conductivity, the impact of the pipes pushed to the wall of the borehole is diminishing. In the field, I have seen the benefits, at best, of 8%. In our hands, it is not worth the hassle.
Thanks for your replies. Waterpirate, I agree that pipe spacers are not useful in mud rotary. Drilling cost is low and conductivity is low = no reason for pipe spacers. However, they are useful in rocky areas where drilling cost is high! Doc, it is true that the pipes' actual position do not fit exactly one of GLD pipe positions. They might be on the outside wall or tangled and closed together. However, since their position is unpredictable, designers using, say, GLD, will always use a ''close together'' or ''average distance'' as a safety net. So designers can not take advantage of the decreased total length/number of boreholes even if the pipes were on the outside wall, because of unpredictability. With reliable (not GEOCLIPS, lol) pipe spacers, you can design the borehole field using a ''spread apart'' position in GLD software. Most design companies in Quebec, Canada that now with the OMEGA EZ-Snaps (the pipe spacer of which I posted pictures above). As for grout conductivity decreasing the spacers' effectiveness, that is also true. But even with high conductivity grout, the pipe spacers still have a good effect. Last Friday, simulating with GLD software, we got these results: Ground conductivity: 2.0 Btu, Grout conductivity: 0.95 Btu, Heating/Coolign load: Don't remember ''Average distance'' total borehole length: 8615 feet ''Spread apart'' total borehole length: 7575 feet Length reduction: 12,07% For 1.4 Btu grout, the numbers are: ''Average distance'' total borehole length: 7860 ''Spread apart'' total length: 7230 Length reduction: 8.01% Now, I doubt 1.4 Btu grout is pumpable. Do you use anything over 1.0 Btu? In conclusion, as Waterpirate said, pipe spacers are worth it for rocks. We just need a pipe spacer that's actually installable! That's why we came up with the Omega EZ-Snaps. Clips easily, allows insertion of the tremie pipe at any time, and stays in place. Make sure to take at look at the installation video on our website: http://www.ez-snaps.com/en.html I'd like to hear what you think of the EZ-Snaps. If they truly are as easy to use as we claim, would you give them a shot? Thanks!
A brief not about conductivity. Mud rotary drilling is cost effective per foot, but the conductivity is high not low in my are of operation. GRTI had one of the highest recorded conductivity tests in the continental USA right in my back yard, drilled by me. Bore was 1x300' with standard 20% grout. aquifer was the Columbian, a unconfined formation made up of mostly saturated sands and some silts, with available water measured in the billions of cubic acres. It is all about location and formation to dictate what tools are implemented. Eric
I'll also add, the drilling costs for soils or rock are the same around here. They just have to setup for it. Overburden can throw a wrench in the works.
Ground conductivity of 2.0 is rare, most of the time it is between 1.4 and 1.9, making higher borehole conductivity less relevant. Yes, we use 1.6 graphite grout as standard, very easy to pump. Lesser ground conductivity + higher borehole conductivity = lesser impact of clips on overall performance
Nobody mentioned the lack of ability to get a grout tremie pipe down the hole with these clips in the way. If you ever Installed a loop into a borehole you will know it’s NOT always easy as it looks on YouTube. Now add the grout pipe to a small borehole with loops installed. Those clips in the picture above will not allow a grout pipe to pass by them. Maybe in a rock borehole, or if you install the grout line with loops at the same time, but that seems unlikely too.
