Has anybody here ever actually did or seen some job where 2 loops were actually installed inside a single borehole? I have 2 DiY'ers in the past week want me to drill for them and install 2 loops per bore to save on the drilling cost. The first job was a 4 ton that wanted 2 300' borehole with 4loops total installed. The second was 6 ton with 3 200' bores with 6 loops total. We decided not to bid on these jobs since we have no direct experience with that set up. And all drillers know, it's always your fault when something goes wrong with the wells and/or loppfield.
These would be 6" bores, in mainly sand and silts in this area. Both properties are going to drill through a aquifer too at around 60-100'
The Ball State University Project, which is the largest geo job in the country with 4000 bore holes, installed two loops in each bore. I seem to remember that you get about 15% improvement over having one per bore.
With only a 15% increase I would be looking at thermal grout before I double looped. At the end of the day it is about the ROI. For some reason homeowners and engineers think a drillers time is theirs to waste. I say bullocks. Time is money and if you want more time youare going to pay. The two loop scenario only works for me when you have to drill a 6 inch hole. Also I see that scenario working best in a rock or shale bore where te hole is very stable, not in a mud rotary bore that is the exact opposite. I have humored every project that has come accrossed my desk and generated a number, and in every case it was cheaper for the buyer to do it our way. Eric
At only 15% it's defiantly not worth it. That seems really low to me though. Has anybody ever seen any actually conductivity test number comparing the two?
The Ball state data is out there, however they did not do a single bore single loop for comparison on that specific site as far as I know. Eric
I bet Ryan can give us more info rcarda@geoproinc.com. Calla, you should email him...he is a good guy to get to know
Unless I misunderstand the whole topic, isn't the main issue how much heat a given area can give? It would seem that the 'double loop' would increase 'heat-exchange' efficiency only. This would only seem beneficial for short operation times ... after that the ground gets as cold with 1 loop as it would with 2 loops. The logic almost seems as poor as digging only 1 trench and putting a bunch of loops in it ... instead of making several trenches (to increase ground area). Or is this just way above my pay-grade to understand?
Engineers forgive me..... Your conclusion is spot on. These topics get driven by pen to paper on a desk, not boots on the ground in the field. I advocate putting as much pipe in a given bore if the hole is in rock with its asociated thermal increase, but not in any other aplication. Eric
With 2 loops there would be a backup if 1 failed ... but how frequently does a vertical loop fail? Also, there would be less pressure drop with 2 loops - but ROI would seem doubtful in many systems. I advocate putting as much pipe in a given bore if the hole is in rock with its asociated thermal increase Interesting ... what types of rock would this be? Shale? Granite? Or would this be porous rock with water flowing through an aquifer (might as imagine the best possible scenario )
I attended a presentation on the Ball State geothermal project at the International District Energy Association this past winter. I recall hearing that they were site limited, so maybe they had to sink costs into the extra loop for the 15% heat transfer gain with the footprint available. FYI, they have over 3,600 bore holes at 400'-500' each. They expect to be using simultaneous heating and cooling most of the year. Bore holes drilled during Phase 1 were 400-ft. deep, 6-in. in diameter with double 1-in. loops, and Phase 2 bore holes will be 500-ft. deep, 6-in. in diameter, and will have a single 1 ¼-in. loop. Maybe they learned something between design of phase 1 and 2. Ball State University - FAQ
Engineering Because I walk both sides of the fence - if you guys ever need some support in going up against an engineer - just let me know. I speak from experience as I have to do it myself often enough.
Wow, 3,600 bore holes is beyond my imagination to visualize. Perhaps the 15% gain was just exchanger performance (as we know it couldn't be the ground capacity). Just a small temp increase can have significant COP improvement. I would presume that during continuous operation, EWT is always less than actual ground temps. With the 2 pipes, there would be only a small improvement in WPD but double the amount of surface area of the pipe ... presuming the heat transfer of a 1" pipe is equivalent to a 1 1/4" pipe [ In another thread, it was stated that the thermal improvement from more surface area of a larger dia pipe is canceled by the increased thickness of the pipe ... basically a wash. ]
