Extra Loop???

Discussion in 'Vertical and Horizontal Loops' started by ELCO Geothermal, Feb 7, 2011.

  1. ELCO Geothermal

    ELCO Geothermal New Member

    I've heard this statement too many times: "we always throw in an extra loop".
    Correct me if I'm missing something! Number of loops and size of pipe is determined primarily by reynolds number (to maintain turbulence). If someone is doing 3/4" loops with one ton per loop on a 3 ton system, that's 3 gpm per loop which is fine, but then they go and throw in another loop for a "safety margin" and end up with 2.25gpm per 3/4" loop (laminar flow). (Based on 25% propylene glycol at 30* EWT, min flow should by 4.43 gpm in 3/4" pipe, no?)
    So I guess my question is: Will the extra pipe in the ground make up for the lack of turbulence?
    For starters, lets disregard the cost effectiveness of this approach and look solely at the functionality of the loop field.

    Thanks folks!
  2. Looby

    Looby Member Forum Leader

    With 25% p-glycol and 3/4" pipe, even 3 gpm leaves you with a
    lower Reynolds# than usually recommended. However, that
    doesn't mean that the flow regime will be truly laminar. It will
    (likely) be "transitional," somewhere between purely laminar
    and strongly turbulent.

    BTW, even at the recommended 2500-3000 magic number,
    the flow regime will still be transitional, but "turbulent enough"
    for comfort.

    And so, the answer to your question is: "Maybe, maybe not."
  3. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Throwing in an extra loop would also include throwing in the engineering to make sure that you are circulating at correct gpm. Adding a cushion to your exchanger is not done without ensuring basic principles of operation.
  4. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I am still trying to justify

    water to watts and suport for Mr. Renolds. I am a hydronics guy in a geo world who can be taught.

    Lobby, I try to get it but I have yet to undestand wearing out pipe from the inside out. I do not think there is anything to the heat transfer issue. I have used Pex, Pex-Al-Pex, hdpe SLR 11, and never noted any differance in heat transfer. i will grant I am not looking for differances to write a paper, but looking at if my customer is comfortable, at amny levels.

    So when I design the system with the reduction due to my antifreeze of choice, I bump the pump. If using ECM drive pumps dial in the number, hit set, go home.

    Eric: You are ON TARGET it is not an extra loop, it is about the total job. Needs and wants. I may be missing a great value added ploy here. If 300' of 3/4" HDPE srd 11 is good in Cleveland Ohio at 12" below building inspecter depth for frost line and building footers depth. If selling a three ton system needing 3 300' loops I could sell 4 loops at 225' each, call it an extra loop and get a bit more for the job and the four hole manifold. Not in this Eagle Scout's life time.

    I am always willing to learn, but I make my living building things that work. I could never work for P. T. Barnum.
  5. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I missed

    paying the digger or driller for the extra.
  6. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    We don't

    We don't do an "extra" loop on our end of things. But you've pointed out a fairly common issue in all construction - the difference between design and as-built. The difference between engineers and "boots on the ground".

    It is important to know how field based decisions effect design performance concerns and how design needs to understand field variables.

    If I specify 478' feet of pipe per loop, I'm pretty sure we will be putting in 500' lengths as that is what we commonly can get the pipe rolls in. Or 1000'. Or 200' for vertical. This is the "applied" in applied science:)
  7. geome

    geome Member Forum Leader

    I wonder if the extra loop is installers (the installers mentioning the extra loop) "clever" marketing idea, or of they are just uncertain as to loop sizing. I also wonder if they would knock something off the price if they were asked to not include the extra loop, and still guarantee the (remaining) loop performance without the extra loop. It may turn out that it's not an extra loop after all, but part of their design.:)
  8. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Yes and no. I am one of guys who tends to have a bigger rather then a smaller loopfields. We shoot to get not lower then 30 F min EWT in the peak of the winter. It is cheaper and faster for me to account for all variables rather then guessing ground conductivity. In terms of pumping power, more parallel loops lower the pressure drop and increase the overall flow. We are doing slinkies, so the flow of water through a curved pipe creates turbulences anyway at lower velocity. So a larger loopfield allows me to skip complexer backfilling or compaction procedures and isinstalled quicker, and allows the loop to perform correctly even in the first year when it is not compacted yet. From the second year on, the customer usually has a slightly higher EWT. So it is a win-win.
    But I always check pressure drop, pumping power to ensure a reynolds number above 2500.
    Last edited: Feb 7, 2011
  9. Looby

    Looby Member Forum Leader

    Then please explain: Why does every p-drop vs. gpm table
    (that I've ever seen) include Reynolds numbers? And why
    do HP manufacturers bother to recommend a minimum Re?
    And why do geo design software packages calculate it?

    What we "believe" has zero effect on the physical universe.

    Last edited: Feb 8, 2011
  10. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    We do not advocate "extra drilling" we push education. For residential we do all the engineering for the gshx. If the issue of the design comes up we educate and let the customer decide how much or how little money they want to spend.
    "boots on the ground" only comes into play for us on commercial work. It is a timeless truth that all the engineering needs to be applied to each specific site to be cost effective, value engineered, or just get done quicker better. That can never happen untill all the trades and the engineers/designers get to the mug lot outside the white trailer on wheels.
  11. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Turbulent flow.....reynolds number......
    Tools of the designer who hopes to put less pipe in the ground.
    Laminar flow works great....(if the footprint is large enough).

    I don't believe in "a little extra loop".
    I do believe in designed results.

  12. ChrisJ

    ChrisJ Active Member Forum Leader

    Extra Loop??

    When I was looking into my Hydro-Temp system 1.5yrs ago, I think their website said something about an extra loop.( I checked the website and I was wrong, they say they use a larger coil, water and air, for a 5 ton unit they use 6 ton coils.)( Don't trust the mind after a year and a half!)

    When I met with installer and loop installer (I had in my head I was getting a slinky), they told me "We need your excavator to dig 6 trenches 250' long, 8' deep", for a 5-ton unit.

    Problem was only 200' available, 250' and they are in the street. Between the two contractors they re-figured for 5 trenches 200' with 1" pipe instead of 3/4" pipe. So essentially dropping the "extra loop". I'm just the homeowner so I have no idea about laminar, reynolds #s. I know my excavator was happy about one less trench. He was getting close to a row of apple trees that were still producing.

    I got a little reduction in price for 1 less loop

    Then the loop installer told me he wanted to add a PVC drip loop. He layed PVC pipes just above, maybe 18-20", loop pipes. Said I can introduce moisture to loop field so it doesn't dry up and be less efficient years down the road.

    Anyone else do drip loops?

    Last edited: Feb 8, 2011
  13. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    "soaker hoses" are part of the installation of DX systems, but I am unaware of a water source company that encourages their use.
    It sounds like your guy might be hedging his bet due to the shortened loops.
  14. ChrisJ

    ChrisJ Active Member Forum Leader

    I don't think the company encouraged it, I think the loop guy had mostly done verticals, no grout in my trenches. I know he was communicating with someone, engineer or designer, he layed the pipe for no extra labor, I just paid for the PVC.

    I figure it will help in late summer to introduce some 55* water to the loop field.
    It's a slight up hill run from manifolds to the ends of the loops. Hopefully the water makes it up there. My excavator has his doubts about it working.

    The installer says temps look good this winter so far, loops doing what they are suppose to. EWT high 30's LWT low 30's.

  15. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    If your loop EWT is in the high 30's this time of year, I would say that you are in good shape.
  16. In Rhode Island, you have more precipitation than evapotranspiration over the course of a year (...so soil will stay moist) thus you shouldn't require a drip line adding moisture to a well designed horizontal loop.

    This is unless you are in some very unusual geologic conditions of expansive clays and also have a delta T that is incredibly high enough to dry out the soil (like a DX system sometimes can).

  17. ChrisJ

    ChrisJ Active Member Forum Leader

    Like Joe said, he was trying to cover his behind for each loop having 100' less pipe. I wish they would have put the 6th loop in. I tried to contact the loop installer, phone number out of service, website gone. I sure hope it was well designed, temps seem fine for the cold weather we have had this winter.The soil was very hard digging, the excavator said.

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