Ground loop or Pond loop

Discussion in 'General Discussions' started by Eric D, Feb 28, 2008.

  1. gabby

    gabby Member Industry Professional Forum Leader

    I'll be saying ya'll and afixin around Xmas.
    Xmas in Texas is like looking at Xmas lights on the fourth of July.....The rugrats and I will drive their parents nuts.
    It's not nice to make me wait for foundation drawings....

    You'll have to travel the beltway with Steph....
  2. crew2000

    crew2000 New Member

    Are you sure that there will be always enough water in your pond ? In dry summer, maybe 3, 4, 5 .... years from now ? Few weeks ago we just switched one house to the ground loop just because pond was slowly loosing water.
  3. jwills8606

    jwills8606 New Member

    Rick - did you ever get a good answer to your question? I live in Farmville, about 50 mi. south of C'ville. I just installed a 2-ton unit with a stainless steel pond heat exchanger plate. My pond is 12' deep/2acres. My plate is sized for 8 tons; I am planning in the spring to convert my 2-and 3- ton air-source units (big house - three heat pumps) to geothermal and wanted the extra capacity.

    It doesn't really matter which is better now; I'm committed to the pond. Interestingly, I had the installer put thermometers in the source and return lines. They are BOTH running about 33 degrees F right now, with the pond frozen over, but it was nearly the same before it froze. The exchanger is so oversized for the one unit that there is never more than a 1 degree delta-T, but I wonder if I would have been better burying pipe at 5'/58 degrees. I'm expecting about 70 degrees pond temp this summer, but don't know for sure yet.

    Let me know if you find a real answer from someone who KNOWS.

  4. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Jim, 33° does not seem right for your situation.

    You should be seeing closer to 39°
  5. jwills8606

    jwills8606 New Member

    I just went to the equipment room and looked at the thermometers. Supply 35 degrees, to the pond 33 degrees. The thermometers are pretty wide-range analog units, but I can read them to about 1-2 degrees.

    Do you have an opinion about which is more energy-efficient - pond loop or ground loop - with maybe a reference somewhere explaining why?


  6. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    If you leave cost out of the equation, you can get greater efficiency with a ground loop.

    Here are two ground loops that are currently supplying 45° to the heat pumps.

    My House

    Another system that I installed

    Most pond loops in the north will have EWT's less than 39°.

    With ground loops you can keep the EWT's in the upper 40°'s

    Of course, you will pay more for the ground loop to be installed.
  7. gabby

    gabby Member Industry Professional Forum Leader

    Life is full of exceptions. Dewayne is correct with his statement with a high percentage of ground loop installations. Rocky, dry soil would not follow those specifics, neither would a very deep lake (30 feet) with a frozen top....the water is warmer on the bottom in cold climates.
    Frankly, I don't believe your readings...but then you might be on the polar cap and thus another exception. I think your gauges are not calibrated, thus even if you can read within a degree, it means nothing with a 5 degree gauge error. I have taken my share of water reading around the country (nothing out West) and the coldest winter temp for 12 foot water I have seen is 43 degrees with a frozen top. You can google water temp sites across the country (find your area) and that will give you a running range of temperatures at different depths....30' is about the average depth for a constant reference point, but they show a graph that includes 12' temperatures.
    Cheap analog gauges are for general temps...not for documentation. A good analog gauge has a method to calibrate the range at 32 degrees and 212 (100 for our Canadian friends). Stick the thing in an ice-water bath for about 10 minutes and see what it reads....should be exactly 32 degrees unless you are in Denver, or Death Valley. I like my analog because at about $20 it is faster to get information, it has a 7" stem for sticking in the ground, and under HVAC pipe insulation...and lately to measure the flowing spring water in a 2" pipe.
  8. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    I am pretty sure that if a lake has ice on top, the water in the lake can't be warmer than 39°. Below is the explanation for this:

    Here are several links that state the same:

    Link 1

    Link 2
  9. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Do not get me started guys.

    Gabby: WB will be in Tigertown this week when it is warmer. Scott got the spring thing to his liking and I am sure it will work.

    DeWayne: Your pond numbers seem low for an Ohio pond. We are taking the monster home and the service van to Valley City tomorrow, and will set up for EWT and LWT and report back. We have 6" of ice on the pond now.

    BTW we need to go elsewhere for IP service. Heat first IP later. Ask Gabby, he has been on sight.
  10. geoloop

    geoloop Member

    I am a geothermal installer local to your area.....I would be glad to work with you on your project.

  11. gabby

    gabby Member Industry Professional Forum Leader

    Two things about lakes...location and water inflow affect water volume temperature equilibrium. The water charts for Virginia are not the same for Texas or Ohio. The links are good but not a true picture of lakes across the country, that's why I suggested he look up his location. The mean temperature of 39 degree equilibrium takes a while to attain. I have never spent a couple of months charting temperatures in one location, so my numbers may be high for the dead of winter in Minnesota, but not for Tennessee, or the Carolinas. I'm sure the people in Florida think their lake water will freeze this week, but I think the massive volumes will need more than a week of sub 32 temperatures to reach that conclusion.

    The bottomline is we are both telling you that location and depth will effect your readings, as well as any error in your instrumentation.
  12. jwills8606

    jwills8606 New Member

    Haven't been here for a while, but I think we are getting off topic. The question was not whether my gauges are accurate at 33 degrees or 40. Seven degrees doesn't concern me, although to see two new gauges off exactly the same amount would be unusual.

    The question is whether it is more efficient to use a pond loop, where the pond freezes over and the temperature varies considerably - about 80 degrees in the summer when you need cooling, down to (OK - 39 degrees) in winter, when you need heating - or whether a ground loop at 58 degrees year-round is better. The thermal flywheel effect of the pond remaining warmer than the fall air for a while and cooler than spring air for a month or so might make the pond choice just fine.

    Does anybody know for sure? Thanks.
  13. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    The Ground

    The soils are always warmer than water in winter and cooler than water in summer. So dirt wins on that. Water wins through convection.
  14. jwills8606

    jwills8606 New Member

    I apologize; I am not being clear. The question is, overall, spread over over a period of years, which is the most energy-efficient? Not just in the winter or summer, but overall - over all seasons?
  15. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    I'll stick to my guns as generally in the shoulder seasons you have little demand. You've hinted the peak lake swings likely correspond with peak load demands.

    But, it would definitely be climate dependent and monitoring, after the fact, would be the definitive answer. Prior to that, you could make some assumptions. The monthly building load demands can be calculated. Monthly lake temperatures may be available through some source.
  16. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Not true. Our ponds go down to 36F EWT in the winter, but horizontal ground loops go down to 30F. In the summer they run up to 80 F EWT in cooling mode, while the horizontal loops only reach 65F.
    Here is the EWT over the season in Buffalo NY Climate.
    Open loop: Temperature and Energy logging by: Web Energy Logger
    Closed Loop Temperature and Energy logging by: Web Energy Logger

    Since we run 90% for heating and 10% for cooling, the ponds are great. That dynamic changes in cooling dominated climate when pond are heated up too much in cooling dominated climate. If the sun heats up the water, it is counterproductive. Things change again when you have flowing water fed by a spring.
  17. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Yep true

    I'm talking soils/water, while you're talking loops.
  18. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    The efficiency question about loops is the same year after year as is the answer: The most efficient loop is the shortest one that delivers the required btus.

    The cheapest one to operate?......the one that delivers the highest ewt.

    Does it matter whether vertical, horizontal, pond or open?

    What is the best one for you (or anyone else)?
    The one that delivers the prescribed EWT (summer and winter) for the lowest installed price.
  19. jwills8606

    jwills8606 New Member

    Yes, I know the most efficient one is the one that is most efficient; the whitest bird is the one that is whitest; the smartest kid is the one that is smartest.

    I don't mean to get testy here, but nobody is trying to answer the question. One MORE time:

    Is there a general consensus as to which system offers the best performance (which is to say, which uses the least electricity/btu of heating and cooling), or has this never been tested? It would seem to me that Water Furnace or somebody has set up a test bed with both systems at the same location, and somewhere in their design manuals it says, "a ground loop is generally superior in terms of energy consumption/btu" or "a pond loop is generally considered superior." Nobody is answering that question, but instead is getting off on topics like whether my pond is REALLY 33 degrees or actually 39. That is not the question, nor any of the others.

    "I don't know" is a valid answer, by the way...

    Thanks again.
  20. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    No consensus.

    But I could show a client which one is the more efficient for their building and site.

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