Standing column vs. grouted column

Discussion in 'Geothermal Loops' started by martyg, Feb 19, 2011.

  1. martyg

    martyg New Member

    I'm a "newbie". I'm about two weeks away from contracting for the installation of a GSHP. I have a large lot but it is heavily treed, so vertical wells make the most sense. I've also decided that I prefer the closed loop system to an open loop "pump and dump. From the IGSHPA web site I gather that it is possible to install closed verticle loops in a column of standing water providing the rock and water levels make sense. (Based on a well I drilled five years ago, my site has 17' of overburen and a static water level of 5') .
    I'm thinking that a closed loop pipe in water will be less expensive to install (no grout) and will conduct heat from the pipes to the surrounding rock as well if not better than grout.
    My HVAC contractor is certified and has installed a dozen systems but they were all trench type systems.
    The rep. from the State water management department acknowledged the possibility of installing a standing column system (with 20' of grout to cap the well) but was pushing for a fully grouted well.
    The well driller is insisting on a fully grouted well.

    My question is 1. Can a system be installed in standing water and 2. is it more or less efficient than if I filled the same wells with Bentonite grout?
  2. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader


    More efficient.

    However I have not heard of a Standing column that is capped with a bentonite seal.

    At the end of the day, you should go with what ever the installer is good at or find an installer that is good at what you want.
  3. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    you are confusing two entirely different scenarios.
    a standing colum geo well and a closed loop iserted into a bore hole full of water are not the same.
    1. a true standing colum well is a modified pump and dump.
    2. installing grout in the entire bore ensures several things:
    a, the entire length of bore is sealed to contamination
    b, the loop will be in uniform contact with the geology
    c, you will get anticipated results/performance from the loop feild.
    3. The IGSHPA standard is to grout the entire bore. If your loop installer/driller wants to meet the national standard for his or her work, follow their lead.
  4. martyg

    martyg New Member


    Thank you for your input. I've had two replies from senior members with opposite opinions, thus the basis for my confusion.
    I believe a "standing column" refers to a standing column of water, once it's filled it is a grout column. I'm not dreaming this up! This concept is described on the IGSHPA web site Earth Insights Volume 1 page 1 by Phil Rawlings.
    With a static water level of 5' the loops would be in uniform contact with the surrounding rock, via the water, except for the top 13' of the bore hole (17' overburden - 4' distance where the loops are pulled from the well) where there is no rock but there still is water. The 20' Bentonite fill is used to seal the well from contamination, provide stone contact in the overburden part of the bore and provide continuous contact in the event the water table drops.
    I live in Raleigh/Wake County, North Carolina where the frost line is 12". Our water wells are terminated above ground and the water pipes are brought up through the top of the casing and then back down into the ground. Wells have a simple cover over them to prevent freezing. Since the geo loops need to exit the wells at 4' below ground the State water management people require the a grout seal. I'm sure they must be doing something different in the mountains in the western part of the state and I will investigate that further. I felt like I needed to resolve the issue of water filled vs grout filled first (if the well is grout filled then the seal is a non issue).
    All this leads to the next question. Assuming I terminate the wells above ground and use a pit-less adapter to bring the loops out of the well casing, what happens if the water table drops leaving some of the loop pipe exposed to air in the casing?
    It seams like there are several advantages to a closed loop in a standing column of water, ground conditions being right;
    1. A cost savings of 50% for the bore holes.
    2. Water will facilitate heat transfer as well as grout.
    3. Water will fill the entire well bore including any cracks and crevices in the hole.
    4. If the water in aquifer is moving one would get an added benefit.

    I don't intend to sound difficult, please continue to comment.

  5. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader


    As Joe stated, you are using the term Standing Column in the wrong context.

    I misunderstood your initial post.

    A standing column system does not have a closed loop hanging there in the hole.

    A standing column is a water well that is deep enough for the water to be pumped from the bottom through the heat pump and returned to the top of the well. By the time the return water has reached the bottom of the well, it has exchanged heat with the earth and is back to the original temp.

    So in answer to your question

    My answer is no. Which makes the second question meaningless.

    Sorry for the confusion.
  6. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Pitless adapters and closed loops do not go together either, again a mixing of water well glossary and loop glossary. although the notion that a loop in a bore filled with water will conduct heat faster or better than one encapsulated in grout is mathmatically provable, it does not make it a more attractive option.
    The standard practice is to grout the entire bore.
    Were you saying that the bore is 50% cheaper with no grout?
    Or were you thinking the bore would be 50% more effective without the grout?
    Many times the local health or well governing body knows less than you do about the installation of closed loops and how to do it correctly. No insults intended just a fact. Your loop installer has proposed to do the job to industry standards which in this case exceed local local code, that is a good thing. Get the loops installed the way that your looper experianced looper proposes and be done with it. Sometimes as homeowners "myself included" we get to tangled up in the details that we need not worry about. Hire proffesionals and let them do their thing.
  7. martyg

    martyg New Member

    Standing column vs grout filled

    Thank you Eric and Dewayne, I appreciate your input. I failed to mention that in addition to being the home owner(on this project) I am a contractor, specializing in residential renovations. That makes me a control freak as well as a know-it-all!
    I can see the problems with trying to get the loops out of the well, four feet below the surface, and then sealing them to prevent contamination. In fairness to my installer, he's been so swamped with work he hasn't been down to make a formal study and recommendations for my needs. He just suggested I start reading about the systems.

    Marty Graff
    Marty Graff Custom Homes & Remodeling »
  8. Bergy

    Bergy Member Industry Professional Forum Leader


    If you're such a control freak:eek: why not get IGSHPA accredited? Then you will be a know it all!!:D

  9. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    You missed the most important question: which is better horizontal or vertical loops.....
    You mentioned your installer has much experience with trenched in (horizontal loops), if this is possible on the property in question that is the way you should go as it is almost always less expensive.

    Let me clear up one more thing for you about loop efficiency.....
    Horizontal may be the least efficient loop so we put twice as much pipe in the ground.
    Verticals with higher deep ground temp average use 1/2 the amount of loop in the ground.
    Open loop has little pipe in the ground but has higher pumping cost.

    Do any of these things make system significantly cheaper to run? Probably not, just cheaper or more expensive to install.

    Good Luck,
  10. martyg

    martyg New Member


    Thanks for the thoughts, I was trying to keep my questions focused. I did consider other installation methods but a trench field won't work on my lot unless I cut down lots of big trees.
    With that exception my lot can be used for any of the other install methods. I have a wet weather creek next to the house, between the well field and the house, that runs into a larger creek at the back of the lot, so I could pump and dump right into the creek. I also have two existing wells, I use one for drinking water and the other for landscape irrigation. That well produces 20 to 25 gallons/ minute, has 17' of overburden and a static water level (in July) of 5'. It is 6 1/4" diameter and 128' deep. The water quality was tested as part of a research study by Duke University and is very, very clean and pure. However it is a little hard and and does have some iron in it, 318.2/ppb. Our drinking water well is only 105' deep and produces 20/gpm and does not have the iron in it.
    So I cold do a "pump and dump' but I don't want to waste the water, one must be considerate of ones neighbors. Or I could drill the irrigation well out another 200' and do a pump and re-injection system but I prefer a passive closed loop system that doesn't require the extra pump and water treatment equipment and management.
    And while those systems may be less expensive to install they have been ruled out.

    I am not opposed to spending less for installation and that is what prompted my question about closed loops in water without the grout. Well drilling here in Raleigh,NC costs $9.00/ft. Grouting the wells will cost another $9.00/ft, so you can see why I had to ask the question.

    An example of what sometimes comes from asking the question is that my house is built where it is. My lot was passed over for 15 years as "un-buildable" because County Health Dept. insisted that the left side of the lot had to me set aside for septic, leach field and field repair area. And they required a "fifty foot buffer" from the creek that runs length wise through the lot from front to back. The right side might be buildable but the ground elevation drops about 12' and so you would have to build in a bottom.
    What everyone missed for 15 years is that the 50' "buffer" zone was for the septic and leach field not the house. I just designed a house that fit into the buffer zone.

  11. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    $9.00 per foot to grout is extreme. Are you sure he did not say an additional $9.00 per foot to case? There is a huge differance. Has the driller got any experiance grouting? I would look for a back bid on the drilling from a experianced loop driller before I ever accepted a bid that 50% of the number was for some bentonite mixed with water!
  12. jrh

    jrh Member

    Marty, you are a contractor. Call another grouter. $9 per foot is too much
  13. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Yes and yes $9 a foot to grout is way out of line.
  14. sustainable open loop

    With your localized geology and existing wells with known yield and water quality I wouldn't be so quick to dismiss open loop--despite IGHSPHA's lack of enthusiasm for such.

    There are thousands of residential and commercial open loop geothermal systems out there that have been running for 20-25 years with no maintenance at all. There also should be no need to any water treatment and the pump costs very little to to run when you only have a depth to water of 5'. Injecting the produced groundwater back into the same shallow aquifer means that no water is ever "wasted" and you can even use a low-cost horizontal infiltration bed (smaller but similar to your septic system) to allow the water to properly infiltrate back into the shallow unconfined aquifer.

    Worst case is that--depending on the hardness, you may have to clean out the heat exchanger once a year but if you keep your producing zone shallow at <105' (there is apparently an aquiclude/confining unit between 105-128' deep thus the change in water quality) this would be most ideal and should minimize this need.

  15. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    . Injecting the produced groundwater back into the same shallow aquifer means that no water is ever "wasted" and you can even use a low-cost horizontal infiltration bed (smaller but similar to your septic system) to allow the water to properly infiltrate back into the shallow unconfined aquifer.


    Hey Adam,
    Do you have any refrance material or software recomendation for the math supporting the construction of the water recieving bed? I have wanted to try and do one of these ever since I saw a storm water management bed installed under the super g parking lot using infiltrators. I am very curious.
  16. Everything comes out of the stormwater arena and it seems most of the material suppliers have their own software varying in complexity from Excel spreadsheets to CAD/GIS add-ons. Check out Cultecs offerings at CULTEC Stormwater Design Calculator

    On the Residential side, Doug Walker (Happy Well Driller) may have some recommendations on what works as he successfully uses infiltration chambers.
  17. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Thanx Adam,
    Also I never miss an oportunity to talk to Doug. lol
  18. No problem. If you ever want to put on a mud-drilling geothermal symposium here in Central PA I have 10 acres of 290' deep sand you can drill to your hearts content in my back yard...

  19. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Adam and Eric

    in PA drilling? I would pay to see that.
  20. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    So would I :D:D

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