pond loop design problems

Discussion in 'Surface Water Loops' started by TReepmeyer, Feb 6, 2011.

  1. TReepmeyer

    TReepmeyer New Member

    I have a 25 year well-insulated old wood frame 3000 sq. ft. house in southwestern Michigan (horticulture zone 6a). It was time to replace the original furnace, which was natural gas. After getting 4 quotes I replaced it with a 5-ton Waterfurnace Envision. A pond loop was recommended by the dealer. He put in two coils, each maybe 10' in diameter one on top of the other and weighted down by cinder blocks.

    I have a large (120' oval) retention pond in my front yard, maybe 30 feet from the corner of the house to the edge of the pond. The contractor who excavated the pond 25 years ago told me he took it down 20 feet in blue clay. I thought that perhaps in the intervening time organic material and silt might reduce the depth to maybe 12-15 feet, but I failed to measure it (as did the Waterfurnace dealer) until after the installation when I finally bought a dinghy and found that the pond was really only 6 feet deep, although uniformly so. I don't know what the bottom is like but it must be full of organic material.

    We had a very dry summer and the pond dropped to maybe 5 ft. I grew concerned, but the AC worked just fine, even though it was also a hot summer. However, after I learned what the true depth of the pond was I also grew concerned about the ability of the unit to transfer heat in the winter. I contacted the Waterfurnace factory and they said that their standards for pond loops are for a minimum pond depth of 8 feet. I then talked to the dealer, asking if we should put in asupplemental ground loop before winter set in, just to be sure. He said that the factory's pond minimum used to be 6 ft in depth, that they recently increased that to 8 ft., but that I should be OK because of the size of the pond.

    Well, we were OK until mid-January when the real cold came. I came home one day to find the thermostat flashing "fault", running on auxiliary electric heat, only. I called the dealer and his service technician came out the next day, I think. He checked everything and found that the unit was functioning just fine, but my pond loop was probably encased in ice limiting the ability to transfer heat. He said that a contributing factor was that I had a windmill-driven bubbler in the pond that not only kept a section maybe 10 ft. in diameter ice free, but that also circulated water cooled to the air temperature throughout the pond. Also, I had on the desuperheater which diverts heat to the hot water tank, but adds to the load on the system.

    Now I am stuck with a system that goes into fault more several times a day. If I don't re-set it it will run on auxiliary electric heat exclusively. I expect that my electric bill will be in the hundreds of dollars - and at that I cannot even maintain the heat in the house at 66 degrees.

    I again suggested to the dealer that a supplemental horizontal ground loop be added to the system, but he said he had never installed a hybrid loop system. His recommendation is to add another coil. I am skeptical. Will it be sufficient to add another coil? Should the coils be stacked on each other? Is it feasible to add a short supplemental ground loop? What is going o now with the system going repeatedly into default? Any help would be appreciated
     
  2. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    The first thing to do is shut off the windmill-driven bubbler. The bubbler is one of the problems.

    No way to know if that will solve all of the problem. You are probably out of luck for the rest of this winter.

    Your installer is confused about the WF recommended pond depth. It has been 8'+ for many years:eek:

    Adding another coil to the pond will gain you little.

    If more loop is needed, which is most likely the case, a horizontal loop would probably be the smart choice.

    I am sure that WF can help the dealer figure out how to install a hybrid.
     
  3. TReepmeyer

    TReepmeyer New Member

    pond/horizontal hybrid loop

    Thanks. Any suggestions where I can look for info on hybrid loop systems? I need to research this myself.

    I have two coils in my pond stacked one on top of the other. Should pond coils be stacked or should we move one off so that both rest on the floor of the pond? Or should they be uncoiled either like a slinky or pulled more or less straight?

    Is it best to suspend the coils so water surrounds the coils, or is it OK to let them settle into the muck at the bottom of the pond?

    I appreciate your advice. This is a great web site.
     
  4. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    The most common way of doing a pond loop in a heating climate is the slinky.

    How ever if you pond is not big enough, a slinky loop will not solve the problem.
     
  5. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I confess I'm torn between abandoning the pond loop altogether or augmenting it.
    Given drought left you around 5 feet deep there is quite a bit less heat available there than you'd hope.

    I agree that the bubbler was ill advised for winter, but it likely helps in summer.

    One possible repair for this winter is to switch to open loop and discharge into the pond (with an above ground drain if possible). You would hopefully add pond depth and not run exclusively on aux. all winter. Make sure to restore freeze protection settings if you do this. You also would want to ensure well water quality was suitable.

    For the permanant solution, it might be easier to re-excavate (increase depth of) the pond (assuming installer put enough loops in to begin with).

    Keep us posted.
    Good Luck,
    Joe
     
    Last edited: Feb 7, 2011
  6. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I was thinking of both ideas as well - open loop for now, re-excavate come spring
     
  7. TReepmeyer

    TReepmeyer New Member

    temporary open loop

    It is 30 degrees outside now with 9 mph wind; the system is keeping the house comfortable at 67 degrees on stage 1 only. When it gets cold (e.g., 15 degrees or less) and windy the loop can transfer heat fast enough and the system faults (locks out, I think is the term you use). The bubbler was turned off three weeks ago, but I have no way of knowing if and to what extent there is ice build-up around the coils in the pond.

    It seems to me that the pond loop configuration as it is now is suboptimal but not horribly so - since the system seems to function OK except on very cold days.

    Spending several thousand dollars to put in a temporary open loop seems to me to be throwing money away - it would be cheaper to just let it run on auxiliary heat for awhile when it locks out.

    I will talk to my installer about a supplemental horizontal ground loop, but if I can impose on you guys a bit more, I have a couple of questions about optimal pond loop design:

    • Does slinky layout give better heat transfer than coiled layout?
    • Does best heat transfer occur when the loop tubing is suspended in water (rather than resting in muck at the bottom)?
    • What is optimal length of the loop tubing?
    • Does tubing diameter materially impact heat transfer? If so, what diameter is optimal?
    • Does tubing material materially impact heat transfer. Again, if so, what is best?
    Thanks again for your help.
     
  8. zach

    zach Member Forum Leader

    TR

    I have a document which was shared with me which states in a heating dominated climate a slinky style is recommended for a pond loop. But, I know of successful installs where a coil was used. Search my posts here as I have posted the document more than once.

    I am a homeowner with a nicely functioning pond loop in upstate NY.

    Your questions about loop length and diameter are more of design questions which you may find will not be answered here(at least specific to your situation).

    I pull our aerator right after Thanksgiving. The aerator destroys temp stratification in winter. We've been cold here in NY but the lowest EWT I have seen (and I watch) has been 35*.
     
  9. zach

    zach Member Forum Leader

    And, I agree with Joe and Curt: I'd get a price on rehabbing the pond so it becomes deeper.

    Is your pond now frozen over minus the bubbler? Did it freeze over while the bubbler was doing its thing?
     
    Last edited: Feb 7, 2011
  10. Looby

    Looby Member Forum Leader

    With SDR-11 (or SDR-9) tubing commonly used for geo,
    diameter does not directly affect heat transfer. Although
    larger diameter tube has more surface area, it also has
    thicker walls. Thus, for SDR (Standard Diameter Ratio)
    tubing, the two effects cancel out nicely.

    However, tube diameter can indirectly affect heat transfer
    by changing the degree of turbulence for a given flow rate.
    (This effect should be negligible if there's enough flow to
    keep the Reynolds number above 2500-3000.)
     
    Last edited: Feb 7, 2011
  11. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    • Does slinky layout give better heat transfer than coiled layout?
    Yes

    • Does best heat transfer occur when the loop tubing is suspended in water (rather than resting in muck at the bottom)?
    Suspended

    • What is optimal length of the loop tubing?
    the length has to be balanced with the pumping power

    • Does tubing diameter materially impact heat transfer? If so, what diameter is optimal?
    Looby answered this


    • Does tubing material materially impact heat transfer. Again, if so, what is best?
    Looby answered this
     
  12. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I want to know the

    EWT and LWT to the pond.

    I designed and installed Zach's loops, with his crew, so I have a clue.

    Coils are not good in ponds as a coil will grab the BTUH from a small area of water and as you noted can ice. It the coils have not floated to the surface we may be able to fix this for this season.

    I have a few ideas for spring.

    Mark
     
  13. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I think you are misunderstanding the problem as you discuss loop efficiency.
    Whether suspended or buried in muck, regardless of diameter- everything will work if enough is provided.
    In your case, not enough pond is provided.
    Limp through the winter if you don't wanna go open loop (shouldn't cost thousands), then make the pond deeper.
    Get information on how much loop (and what diameter) was actually installed and we can tell you if it is likely enough.
    Good luck,
    Joe
     
  14. TReepmeyer

    TReepmeyer New Member

    thanks - spring options

    First, I would like to thank all of you who have responded to my initial query. This web site is terrific.

    FYI, it is 17 degrees outside, 67 degrees inside and the pump is chugging along on stage 1.

    I understand that the pond as it is now is not sufficient, but I am trying to now figure out what option is best to pursue this spring. As I perceive it, I could 1) excavate the pond so that it is of sufficient depth, 2) pull the coils from the pond and put in a horizontal loop, or 3) keep the pond loop, move the coils from on top of each other, put spacers in the coils and add a supplemental horizontal ground loop.

    I'm guessing that it is possible to obtain optimal system performance with all three options, so the question is which will be least expensive.

    What do you think?
     
  15. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Try this

    It works in Ohio.
     

    Attached Files:

    Last edited: Mar 3, 2013
  16. TReepmeyer

    TReepmeyer New Member

    remediating the pond loop

    Looks like the best option is to replace the coils with a slinky and add a supplemental horizontal segment to the pond loop. However,

    I will price the pond dredging, but my wife and I have put several years and a lot of work into landscaping. Dredging the pond would make a mess of our front yard and cost us a lot to repair. There is a large lawn on the side of the house where the pond loop enters and exits the house that would be perfect for the supplemental horizontal loop.

    By the way, the pond froze over completely as soon as I disconnected the bubbler, and in any event it only kept an area about 10ft. in diameter ice-free when it was connected.

    Is measuring EWT and LWT something a non-professional can do?
     
  17. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I would want to know what we have before designing augmentation.
    How much loop do you have in the pond.....what diameter?
    j
     
  18. TReepmeyer

    TReepmeyer New Member

    pond loop

    The existing pond loop consists of 1500 ft. of 3/4" polyethylene in 2 coils stacked on top of each other and anchored to the bottom with cinder blocks. I cannot tell whether they have floated up as the pond is iced over and has anywhere from 1 to 3' of snow on it. Pond depth (to top of ice) is now about 7 ft. as filled up this Fall (low point in August was 5 to 5 1/2 ft.)
     
  19. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Looking back to find the

    heat pump size I saw something I missed the first time through your original post. When you replaced the old system did you get rid of your gas line and meter?

    I think one should always use their cheapest fuel for back up or auxilary heat. If the answer to my question is no then I would consider a fuel change for aux heat.

    You could do this:
     

    Attached Files:

  20. TReepmeyer

    TReepmeyer New Member

    answers

    Mark - I have a 5-ton Waterfurnace Envision. The gas is not shut off as I use it for hot water and cooking. I'm not sure what to make of the pictures. The first one seems to be of a A O Smith Vertex water heater. The second one looks like part of the heat transfer mechanism. I must be missing something.

    Tom
     

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