Rock_nj
New Member
Posts:4
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| 08 Jul 2010 12:35 PM |
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I live in Morris County, NJ. I heard from a geothermal installer that they had problems installing the wells for a geothermal system recently in my area because there are large boulders beneath the surface to bedrock at 100 feet below grade. He suggested one large 450 foot well, verses 3 more modest 150 foot wells. Are there any technical advantages or disadvantages to installing one large 450 foot well? I understand my geothermal system will be more efficient with greater depths (not sure why) and I assume there will be some cost savings on the drilling since there will be less overburden well casing and boulders to deal with.
Any input would be appreciated. Thanks!
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engineer
Veteran Member
Posts:2749
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| 08 Jul 2010 01:14 PM |
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I doubt there is much temperature difference associated with 150' vs 450'
As long as the pipe in the bore is sized to balance maintaining turbulent flow vs minimizing head pressure loss I don't see a problem.
Seek references from your proposed contractor and follow up with them. |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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jonr
Senior Member
Posts:5341
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| 08 Jul 2010 01:47 PM |
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If 450' gets you into ground water and 150' doesn't (or even doesn't for the whole length), then you are likely to see a big difference. |
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jonr
Senior Member
Posts:5341
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Rock_nj
New Member
Posts:4
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| 08 Jul 2010 01:51 PM |
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I guess the geothermal loop is better at conducting heat from ground water than soil, thus a higher input temperature for the heat pump? What is the average temperature of ground water?
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waterpirate
Basic Member
Posts:467
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| 08 Jul 2010 04:55 PM |
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It is no fun at all to drill in Morris county!!! The advantage of one deeper bore is that if the driller can successfully dodge a significant boulder in the overburden once, when he hits the bedrock it is all aboard the normal train. Even if he craps out a couple times he is better off to move the rig and try again, rather than try and battle a large boulder. The reason one bore is said to be better in your kneck of the woods is that the bedrock gives better conductivity than saturated sands. Good luck and trust the guy/installer/driller that is going to warranty the work. |
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| Eric Sackett<br>www.weberwelldrilling.com<br >Visit our Geothermal Resource Center! |
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jonr
Senior Member
Posts:5341
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| 08 Jul 2010 05:35 PM |
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Ground water is the same temperature as soil at the same depth and isn't a great heat conductor - but it has big advantages - 1) that it moves and 2) it saturates and increases the conductivity of other materials - so your performance and efficiency is better.
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Looby
Basic Member
Posts:401
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| 08 Jul 2010 06:15 PM |
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What Waterpirate said!
My 3-ton WF Envision runs beautifully on a single 450' bore (in
S.E. PA). Driller got lucky and hit bedrock at 10-12 feet, then
solid wet schist all the way down. The guys trenching from the
well to the house weren't so lucky -- many SUV-sized boulders
in the top 6' of overburden. It took as long to dig the 50' trench
as drilling + pipe-insertion + grouting, combined.
Single-bore advantages:
- simple
- no manifolds
- easy to flush
- minimum # joints
- minimun length of trench
No real disadvantages other than high-ish head loss. Not
a problem with correct selection of pipe and antifreeze.
(1.25" HDPE, 20% methanol, one UP26-99 works for me.)
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| One measurement is worth a thousand expert opinions. |
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Alton
Veteran Member
Posts:2164
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| 13 Jul 2010 05:01 PM |
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Mr. Sackett,
Why is drilling through a boulder near the surface more difficult to do than boring through bedrock? Does the type of rock in the boulder make a difference? So far, my projects had wells drilled in granite bedrock - no boulders that I know of. I do have a project coming up that testing shows to have boulders within 8 to 10 feet of the surface. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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Alton
Veteran Member
Posts:2164
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| 13 Jul 2010 05:21 PM |
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Looby,
Are you saying that a single deep well could require larger diameter pipe than equivalent shallow wells so as not to increase head loss? For example, are we talking about a small change in diameter such as upgrading from 1.25" pipe to 1.5"? I can understand how a deep well with an open line for drinking water could have increased head loss but for a geothermal well with a closed line full of water and purged of air, I would think that the push and pull of the water in the closed system would require the same amount of pumping pressure especially since the total line footage would be the same. Also along this same line, is there a maximum for the depth of a geothermal well? I know there must be something important that I am missing but I can not see it now. A good explanation would benefit me. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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arkieoscar
New Member
Posts:57
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| 13 Jul 2010 09:16 PM |
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Head is referring to all losses. In this case it's the friction losses in the piping which is lower in larger diameters. Look up the tables for different size piping and you will see. The choice has to be balanced because larger diameters require more volume to stay in turbulent flow. |
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Alton
Veteran Member
Posts:2164
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| 13 Jul 2010 10:46 PM |
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Arkieoscar,
Thank you for that explanation but I need more.
I can readily understand why the friction losses would be lower in a larger diameter pipe. I can also understand that a larger diameter pipe with more volume might require a larger pump that uses more energy. But I do not understand why one deep well would need a larger diameter pipe and pump than three shallower wells that equal the same footage. In other words, why does it matter to the pump whether the water goes up and down in three 150 foot wells or just one 450 foot well?
I have seen geo installers fuse pipe together and say that the ridge inside the pipe will cause turbulence that is beneficial to conduction. I grasp that turbulence can increase friction losses. I am still having trouble wrapping my mind around why the same size pipe and and number of joints in a deep well versus three shallow wells would not have the same friction (head losses)? What am I missing here? I am not arguing. I want to understand the physics. I must be missing something very basic. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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waterpirate
Basic Member
Posts:467
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| 14 Jul 2010 06:34 AM |
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As gpm goes up so does friction loss. You can push a significant volume of fluid through a very small pipe with increased hp up front, and diminished flow and pressure at the end. As the depth of the loop increases the diameter of the loop does also to keep the pump hp at a minimum and keep velocity where it needs to be. IGSHPA has numerous charts and graphs explaining this as well as some of the unit manufacturers in their loop design info.
The differance between drilling boulders and bedrock is best explained that the boulders can move,shift, and fracture in the overburden, Bedrock is bedrock. Imagine drilling a hole in a chunk of wood that keeps moving, then it cracks in half and bridges the original hole. OMG
Eric |
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| Eric Sackett<br>www.weberwelldrilling.com<br >Visit our Geothermal Resource Center! |
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Alton
Veteran Member
Posts:2164
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| 14 Jul 2010 08:02 AM |
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Mr. Sackett,
Thanks. I really appreciate your answer. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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jonr
Senior Member
Posts:5341
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| 14 Jul 2010 08:04 AM |
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If you put 3 150' well in series, then the friction losses will be the same as a single 450' well. But if you put them in parallel, that is similar to using a larger pipe which has less resistance (a larger volume pipe does not require a larger pump).
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Alton
Veteran Member
Posts:2164
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| 14 Jul 2010 08:23 AM |
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Jonr,
Thanks. Serial versus parallel flow! Now I understand the Physics. I forgot about multiple wells using a manifold to create parallel flows.
Over the years I have learned so much through Green Building Talk. I appreciate each and every posting. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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Looby
Basic Member
Posts:401
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| 15 Jul 2010 01:48 AM |
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Alton,
Parallel versus series is one key difference. A parallel configuration
has less pressure drop, but also less flow (gpm) in each parallel
branch -- and thus, less turbulence.
Turbulence is the second key consideration. If flow within the loop
is not sufficiently turbulent, heat exchange efficiency will suffer.
So, loop-field design is a matter of finding an acceptable trade-off
between pressure-drop and turbulence.
http://waterfurnace.ca/Engineer/Misc%20References/Pressure%20Drop%20Calculation%20Instructions.pdf
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| One measurement is worth a thousand expert opinions. |
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jonr
Senior Member
Posts:5341
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| 15 Jul 2010 07:16 AM |
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There is a large list of important considerations - soil, length, water level, grout, number of tubes, tube spacing, coaxial tubes, turbulence, tube material, casing, etc. It would be short sighted to focus on only a few of these - and all of them can be traded off (to some extent) with the others.
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Looby
Basic Member
Posts:401
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| 15 Jul 2010 12:53 PM |
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Uh, you forgot coriolis.
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| One measurement is worth a thousand expert opinions. |
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waterpirate
Basic Member
Posts:467
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| 15 Jul 2010 08:18 PM |
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It is funny to me how small the world really is. My phone rang today from a good freind in n.j. He said he had a tuff case in that may require a horizontal system due to the drilling conditions? I asked if it was in Morris county, there was a pause and he said yes. Anyway he needed help with loop design and I sent him to Pallace Geothermal.
P.S. the drilling conditions in morris county are 100 times worse than I portrayed! lol |
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| Eric Sackett<br>www.weberwelldrilling.com<br >Visit our Geothermal Resource Center! |
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