NTXbiofuel
New Member
Posts:4
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| 28 Jul 2010 11:25 AM |
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Hello all, really glad I found this forum to help me with my geothermal purchase. I have several questions concerning geothermal installations for my new home. I know I want the geothermal and have even purchased the huge IGSHPA book on installing geothermal so that I would have at least a fighting chance when speaking with contractors. I'm a civil engineer by trade and enjoy "heavy" reading and feel I have a basic understanding of the process so what all the contractors are telling me is confusing.
I live on a 5 acre tract in the Cross Timbers soil area. When my on site septic system was installed I had the backhoe operator dig several test holes on the property to determine soil type and depth and was interested in the subsurface temperature also. While unable to measure the soil moisture, I did get readings every foot down to 8 ft. (in a properly benched hole) These readings were consistent with my book learning and the soil strata was consistent with the TX soil map so all is good to this point.
Fast forward to inviting contractors to bid on the structure and mechanicals. All three of the geo HVAC contractors insisted that the only possible way to install the ground loops were vertical bores. "Horizontal will not work in TX" was all that I heard. Only one gave a reason and that was that the loops would have to be so long that the pumping requirements would overcome all geo savings. I did not want to get argumentative but using the most conservative thermal conductivity and soil diffusivity right from the book, I was able to design a loop from the book data that was an increase in pipe size from .75" to 1" to overcome the head loss, use only the -99 pumps using the pump curves and come up with loop temps from 30 to 90 deg. Since I know my way around soil excavation costs, going vertical with the bids I received vs. trenching will cost at least several thousand more. The IGSHPA handbook even states there is no best loop configuration when properly designed and installed on the first page of Chapt 5. My contractor choices here are limited and I want to avoid a DIY project over my abilities so the bottom line is, will a properly designed closed loop geothermal system work in North Texas if the ground loops are installed horizontally or must I go with the vertical system?
Second question. The IGSHPA certified driller the contractors want to use is $$$$ more expensive per foot than area water well drillers. I've spoken with several master drillers who drill municipal wells and grout them per water resources specs. From my book learning it seems as long as the driller drills to the proper depth, installs the piping per manufacturer specs, uses a 1" tremie pipe to the bottom and grouts within 24 hours with a grout that meets geothermal conductivity and shrink-resistant properties, that the geothermal well is within IGSHPA specs. Therefore what advantage is there to using a certified IGSHPA driller vs. the person who is a licensed master driller and adheres to all procedures? Would the equipment manufacturer not honor a warranty perhaps? Other than a possible warranty concern and experience placing a ground loop in the hole and grouting from the bottom up, is there something special about an IGSHPA certified driller?
Thanks in advance for reading thru this. |
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fsq4cw
New Member
Posts:64
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| 28 Jul 2010 03:55 PM |
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Your logic sounds good to me (an accredited IGSHPA installer). However, I’m not in Texas. I would speak with the accredited IGSHPA driller and ask him why you should go with him. I don’t see why a horizontal ground loop wouldn’t work in your area unless perhaps the ground can become very dry. You may also want to consider a ‘slinky’ horizontal ground loop system as well.
SR
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NTXbiofuel
New Member
Posts:4
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| 28 Jul 2010 04:55 PM |
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I don’t see why a horizontal ground loop wouldn’t work in your area unless perhaps the ground can become very dry. You may also want to consider a ‘slinky’ horizontal ground loop system as well I agree that the ground can become very dry in my area. That being considered, if I use the thermal properties from table 5.15 in the IGSHPA installation book and use the most restrictive thermal conductivity properties (wilting point of my particular soil) a horizontal loop should still work. Using design criteria for a slinky coil will use too much pumping power vs. my 1.00" design when the ground dries to the wilting point. |
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jonr
Senior Member
Posts:5341
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| 28 Jul 2010 06:09 PM |
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Depending on layout, you can put some loops in parallel for lower pumping costs. You may want to look at simulation software such as "Ground Loop Design" - much better than tables. Personally, I'd throw a soaker line down in with the loops - who knows when you will get far-out-of-the-norm weather and need it. Or consider open loop or a standing column well. |
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engineer
Veteran Member
Posts:2749
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| 28 Jul 2010 08:53 PM |
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Sounds like you have done your homework. I'm in Florida and have no experience with horizontal fields but have heard from a geo well driller that it requires 1000' of horizontal pipe per ton owing to our warm, sandy, and sometimes dry soil.
You could take it a step further, do the loop design and stipulate that you will be responsible for loop performance. That should bring the price down toward that of a high end ASHP.
We had a member here a year or so back with a horizontal system in the deep south that essentially failed during extremely torrid weather. If memory serves the issue was one of long-delayed soil consolidation around the loop lines, helped by heavy watering. I would consider watering the heck out of the lines when they are partially buried, maybe 1 foot under dirt part way through backfill. Then again, you are a Civ E, so you probably know your way around soil consolidation.
As to question 2, I agree, but you list a bunch of "ifs" If a standard well driller can do all the extras, that's fine...does he/she have the HPDE fusion welding tools and skills needed to fabricate reliable U-tubes?
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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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NTXbiofuel
New Member
Posts:4
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| 28 Jul 2010 09:41 PM |
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Depending on layout, you can put some loops in parallel for lower pumping costs All my current calcs are based on a reverse return parallel layout. My current worst case design, for soil with conductivity of .39 for a load of 22K btu cooling is 4020' of .75" supplied by 2- dash 99 pumps. I show a reynolds # of 2814 and a flow rate of 10GPM. If memory serves the issue was one of long-delayed soil consolidation around the loop lines, helped by heavy watering. I would consider watering the heck out of the lines when they are partially buried If I decide to pursue the horizontal route, with this information I will probably jet in the ditch when 1/4 filled to help settle the soil all around the pipe. I'll have to check with my driller on the fusion issue. Very likely he does not have the fusion equipment or experience in this area. He did however mention using BH20 grout...checking the specs on this product it appears it only has .45 thermal conductivity. Will this make a huge difference in my expected efficiency if I decide to go the vertical route or should I use the thermally enhanced version? |
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Down2Earth Geothermal
New Member
Posts:59
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| 28 Jul 2010 10:09 PM |
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A properly designed horizontal system will work fine in TX. If you choose to go vertical, ask the driller what the cost will be for a higher TC grout. Run the design with high TC grout and with regular grout to see how much borehole you will need for each and you can calculate each respective cost to make a decision. You will need to know the borehole diameter for this as well.
A high TC grout in a large-diameter borehole installed in a highly dense fine-grained sandstone may allow a reduction in the borehole length by 20% or so--but most water well drillers may not have the equipment to mix and pump this grout so the increased cost may not be cost effective.
-Adam
Hydrogeologist |
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joe.ami
Veteran Member
Posts:4377
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| 28 Jul 2010 10:38 PM |
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Local geo guys may have been once or twice burned by drought. As contractors we have to promise performance no matter what. As a DIY guy you may be fine with horiz. loops and the odd soaking with a buried hose.
RE drillers, If grouting substance moves therms as quickly as surrounding material all is well.
Here's the real question I pose to all customers who have studied the questions as deeply as you......
"Who do you want to be responsible for the performance of the system? One of us will design it and that person will be responsible for the results."
This is intended to be practical, not adversarial. I know that it reaches -18* in my area but design software says 3 hours/yr of -8* worst case; on a 20 year average they are correct. Would you be a happy customer, however, if I could only get your home to 60* during extreme cold weather (or for Texans, 80* during extreme hot weather)? If your install savings is $10,000 the answer could be yes! You still won't have a local contractor recommend it, 'cause it is cheaper to lose a job than fix one with a design that may not keep customer happy all the time.
You might be thrilled to save the money and run the hose when it's hot and dry. That's great, just make sure you avoid suprises.
Good Luck,
Joe |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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waterpirate
Basic Member
Posts:467
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| 29 Jul 2010 06:29 AM |
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In regard to your querry about master well drillers, the answer is not exactly. Geo loop drilling is what is termed production drilling. That means that it is fast, effecient, and repetitive. Everything that waterwell drilling is not. Most drillers who are not geo freindly get easily discouraged by the problems geo drilling present and they determine that it is not profitable for them. example= 4.5 inch bore to 200' loop installed and grouted by good geo guy 35 minutes. Same example water well guy 2-4 hours.
The grout question comes up alot. The advantage of thermal grouts above .45 on a engineered project is that it allows a reduction in total footage required for the exchanger. On residential projects it is voodoo, you are applying enhancements that cost money to a unknown value of actual conductivity. Hope this helps.
p.s. with a correct design upfront a horizontal can work in TX |
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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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| 29 Jul 2010 07:28 AM |
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Adam is correct. Thermally, the better thermal conductor the grout is, the better the system performs. Like any insulation, diminishing returns, but never zero returns. It's basic physics. Simulation software makes it easy to estimate the difference. At what point it becomes impractical (ask your driller) or non cost effective (do the numbers) is another issue.
Multiple U-tubes and spacers (to keep the tubes close to the borehole wall) are similar. Also consider where the water level is - getting down to it helps (one 300' hole will outperform two 150' holes if water is at 100').
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waterpirate
Basic Member
Posts:467
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| 29 Jul 2010 06:55 PM |
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I would love to see the cost calculator/annalisis for a multiple u tube assymbly in one bore hole with spacers installed useing a high tc grout for a typical residential job. We are getting people with legitimate questions hung up on minutiae that is cost prohibitive for roi. I will once more state that using a thermally enhanced product to reduce bore hole footage by as much as 20% in a borehole that has not had a proper conductivity test done to verify data is crap! The more/better insulation argument just does not stand up to the cost for what? A variable that can not be measured or proved. That is money well spent? I have a bridge for sale, please pm. |
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| Eric Sackett<br>www.weberwelldrilling.com<br >Visit our Geothermal Resource Center! |
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engineer
Veteran Member
Posts:2749
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| 30 Jul 2010 12:58 AM |
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I don't have the benefit of long experience with loopfield design but my gut suggests that more than one U in a bore is lunacy - the multiple parallel paths will steal from each other, provide little net increase in heat transfer, drive up both installation cost and pumping power.
There have been a couple threads lately about boreholes separated by 10'. What little I know suggests that 15' is a better minimum and 25' better yet - the more dirt invited to the heat exchange party, the better. Clustering multiple bores in the same mass of dirt seems to me risking that the bores affect each other.
Multiple Us in a single bore would seem to me to perform like two bores just 2-3 inches apart, and no one does that... |
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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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Looby
Basic Member
Posts:401
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| 30 Jul 2010 12:59 AM |
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Posted By waterpirate on 29 Jul 2010 06:55 PM
I would love to see the cost calculator/annalisis for a multiple u tube assymbly in one
bore hole with spacers installed useing a high tc grout for a typical residential job.
If individual bores should be separated by a minimum of 10-20 feet, what
can be said about the 'logic' of jamming two u-tubes down the same hole?
Even if you replaced all the HDPE and grout with 99.999% pure silver, it
wouldn't do diddly for moving BTUs through the surrounding soil/rock.
Where is some evidence that the thermal resistance of a 3" radius bore
hole is significant -- compared to the (series!) resistance of tens of feet
of surrounding soil/rock?
...BTW, would you like to buy some MonsterCable™?
Looby
"A fool and her money are soon courted."
- Helen Rowland
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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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| 30 Jul 2010 08:00 AM |
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while there are several double u tube jobs in the ground a few finer points need to be made:
They are commercial
The conductivity testing was done with 2 loops installed
They are hard rock bores where the cost per foot is high and the diameter of the bore is governed by the hammer
There is no long term data available yet to determine anything
This is the ever present disparity between commercial and residential work. Commercial work is Enginneered with real data for a specific location on the planet. A PE or better signs off on and garauntees the performance of the exchanger. Some peoples willingness to believe that because it was done on a commercial job it has an application on a residential job in a different region of the country just baffles me. Design without data is malpractice. Plain and simple. It is also widely accepted that increasing the conductivity of grout beyond .85 only adds cost in most cases without seeing appreciable return on your money. If you would use Ryan Carda's borehole calculator you would see this as it accounts for material costs and labor. If you want a good chuckle ask him about the beer induced conversation he had at a pub with some guy about bore hole spacers and the pictures that were drawn on the back of cocktail napkins. The other party to that conversation then invented bore hole spacers and took it to market, that still does not make it better or more effective or labor saving. |
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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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| 30 Jul 2010 08:42 AM |
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There is lots of data, lots of simulations (with verification) and the physics of multiple u-tubes (or spacers) is simple. They are common in Europe (even for residential). Thermally they perform a little better, whether they are worth the extra costs depends. Go do some reading (or try it on one hole and compare temperatures if you don't trust researchers).
I can't imagine why someone would think that something simple like multiple U-tubes or better grout requires individual conductivity testing but a far bigger and more variable factor like length or ground water level doesn't. Why should I pay for an extra 100' of borehole without a thermal test to verify that it is better? "Design without data is malpractice"?.
If you think that within borehole thermal conductivity is unimportant, I suggest wrapping the tubes with an "insignificant" 1/2" of foam insulation - let us know how well it works.
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geome
Advanced Member
Posts:987
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| 30 Jul 2010 09:08 AM |
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I'm just trying to learn. Is there a typical percent benefit to having the spacers or multiple u-tubes? Would overall bore length be reduced, or is this done to increase efficiency above what is normally expected in a like sized hole? Is this a situation like replacing a head gasket on a car, with a $10 gasket and hundreds of dollars of labor to do it right? Would this contribute to the ground possibly retaining more (or less) heat in a given area over time (years) that was discussed previously in another thread? Has anyone here successfully done this, or not had success doing this and what were the problems encountered and what would have been involved (including time & cost) to overcome the problems? |
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| Homeowner with WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon. |
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waterpirate
Basic Member
Posts:467
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| 30 Jul 2010 10:14 AM |
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Posted By jonr on 30 Jul 2010 08:42 AM
There is lots of data, lots of simulations (with verification) and the physics of multiple u-tubes (or spacers) is simple. They are common in Europe (even for residential). Thermally they perform a little better, whether they are worth the extra costs depends. Go do some reading (or try it on one hole and compare temperatures if you don't trust researchers).
I can't imagine why someone would think that something simple like multiple U-tubes or better grout requires individual conductivity testing but a far bigger and more variable factor like length or ground water level doesn't. Why should I pay for an extra 100' of borehole without a thermal test to verify that it is better? "Design without data is malpractice"?.
If you think that within borehole thermal conductivity is unimportant, I suggest wrapping the tubes with an "insignificant" 1/2" of foam insulation - let us know how well it works.
Thank you for making my point. The disconnect here is theory vs. reality. Or cost vs. reality. It is one thing to do some reading on the "intra net" and quite another to implement. Geome makes an astute observation using the car analogy. Those clips are cheap, loops are cheap, tc grout is cheaper to purchase, but the labor neccessary to implement any of those things let alone a combination of them would drive the price to install a non engineered exchanger beyond what could ever be hoped to gain in increased effeciancy. I have stated also that "if" you pay for a thermal conductivity test you can use that data to design the system any way you see fit. If you do not perform testing you are adding significant cost to a project for a "percieved" roi and no way to verify any gain or loss to justify the additional costs associated with them. Every area of the country has a different set of geology to work from. You either trust the local guy and install what has a proven track record or you do not. So if you are willing to implement the clips, the tc grout, the double u tubes, and magic fairy dust to shorten the depth of bores in an unknown lithology I hope you have really good insurance. I also am not going to discuss this with you any further in an attempt at community harmony. |
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| Eric Sackett<br>www.weberwelldrilling.com<br >Visit our Geothermal Resource Center! |
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NTXbiofuel
New Member
Posts:4
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| 30 Jul 2010 12:08 PM |
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Wanted to update all and get an opinion. Talking with a water well driller concerning the subsurface structure in my area. It is normal to hit a water-bearing strata at approx. 150' and the cuttings are usually blue shale followed by sandy gravel. He uses BH20 for the grout. From reading the previous posts about drilling, can I assume (and I hate to assume anything) that the lower TC of the BH20 (.45) will insignificantly affect the borehole performance? He uses geo-designer from climatemaster and his calcs using this software are very conservative with regard to borehole depth, ie., program indicates 280' deep (560' total) of .75" needed per bore and his recommendation is 300'. The added length will not affect the GPM or the Reynolds numbers in any meaningful way per his software.
For my shop I'm planning a horizontal and going with the absolute most conservative TC. Additionally I plan on installing an underground soaker 2 feet above the piping. Also I will jet and soak the first two feet of fill that is placed in the ditch. I'm planning on using the WEL logger to document all performance of the vertical vs. horizontal systems.
Thank you for all your input. |
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Looby
Basic Member
Posts:401
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| 30 Jul 2010 12:25 PM |
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Posted By jonr on 30 Jul 2010 08:42 AM
Why should I pay for an extra 100' of borehole ... ?
It's only an "extra" 100' of borehole if you started out with an
absolute best-case assumption about the possible benefits
of the MagicalFairyDust du jour.
In effect, that's designing for: "The minimum length of borehole
for which I can't prove that it won't work."
...a favorite algorithm of Dilbert's pointy-haired boss,
Looby |
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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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| 30 Jul 2010 01:08 PM |
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geome, if you are really interested, get some more advanced simulation software like "Ground Loop Design" and try different designs. It even accounts for the year-to-year effects and adjacent borehole effects. Or, if you can't imagine software being close to reality, try one real hole. Lots of people have used double u-tubes - apparently just not someone in this forum. The difference depends - 13% for one random example.
> very conservative...program indicates 280' deep (560' total) of .75" needed per bore and his recommendation is 300
The potential errors in estimating are larger than 7%. So I wouldn't call 20' extra "very conservative". Grout quality makes a fairly large difference (say 30%), so it's a poor place to cut corners (although your well driller will be happy to drill another hole to compensate).
I can't even comment on people who think that whatever design they have in their head is the one correct and proven design that will perfectly match actual performance and anything different is unproven and unnecessary or risky speculation. They are easy to spot - look for the name calling.
http://litchfieldgeothermal.com/REHAURAUGEOETC.4BoreholeThermalCondTestResults101409.pdf |
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