Can a geothermal loop work efficiently in an iced over pond?

Discussion in 'Surface Water Loops' started by mangumjs64, Feb 18, 2011.

  1. mangumjs64

    mangumjs64 New Member

    My intent here is to get some insight on a system gone wrong. We had a pond loop placed in our pond during construction of our home a couple years ago. The installer designed a system with three coils of 500', 1 1/2" pipe. The coils are about 1 1/2 ' high by 4' by 4'. All told with the run between the coils and the house there is about 1700' of pipe. The depth of the pond is about 15' where the coils are. The system works great in the summer but the compressor freezes up in the winter. Incoming temps to the compressor range from 40 to 36 degrees when the pond is frozen over. The installer is suggesting we replace the coils with slinkys across the floor of the pond. Maybe it will work.

    I do not want to go through another winter living on kerosene heaters.

    I brought in a pond managment consultant to measure the temps at the bottom of the pond while it was frozen over because the installer did not have any equipment. The readings were all 40 degrees on the floor. As soon as the equipment was raised off the floor the temp dropped to 35 degrees. The consultant told me that due to the physics of the water as it freezes the water in a frozen pond will be too cold to run a geothermal loop in the winter. As I understand him and physics, the water stratifies with the coldest water on top, water that is about 35 - 33 degrees on the bottom and water that is above 35 degrees is in between. The only reason that the water on the floor is 40 degrees is because of the ground temp.

    Is the consultant right? Will an iced over pond produce enough temp to run a geo heat pump?

    Any insight is greatly appreciated.
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Should work just fine. Temp at bottom of an undisturbed pond is 39*F

    Compressors don't freeze. Loops do. Some antifreeze in the loop will protect it from freezing down to 15 or so. The heat pump should have a setting (jumper or dip switch) allowing it to run with freeze protected loop fluid down to 20*F or so.
  3. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    The ewt should be fine to support your unit. Does your system have any antifreeze in it now? Given the temps in the mid atlantic this year, extended run times for your system could have gotten your ewt to a point the unit locked out on freeze protection. Ensure that you have anti freeze down to at least 15 degrees if not more. Verify the jumper for closed loop operation has been cut, most units come from the factory set up for open loop. Has your installer ever done a pond loop prior to yours? Switching to a slimjim will not change the data in your pond. If you find that you do not have enough loop, I would look at adding more loop prior to re-inventing the loop.
  4. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    1500' of 11/2" loops is a lot of pipe (depending on heat pump size).
    The answer to your troubles is not going to be found in the information you have given us.
    We don't know flow (GPM), entering and leaving water temps, size of heat pump, antifreeze protection etc.
    You could be underlooped, you may not be circulating enough brine, your loops could be poorly flushed, your antifreeze may be inadequate, your tech might be out of his element your pond guy doesn't know anything about geo.
    Little we can offer without more info.
    Good Luck,
  5. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    My favorite is

    pond loops. And the three guys above me are correct. Feed us some more data and I am sure we can make it work ..

    I just lost my laptop with all my pond links. Palacegeo sent me a great work up by the Ohio State University Sea Grant program on pond stratification, so I can prove engineer's statement of 39* water all year long.

    Zach still has a link to a piece by McQuay on commercial pond loops. Eric and I may disagree about plastic vs metal but we are all on the same team.

    Here are a few shots of a pond in Valley City OH, done over a four year period. The older loops (orange) feed a 5 ton water to water, and gives me EWT of 41* with 12' of ice on the pond.

    Attached Files:

  6. Forum Admin

    Forum Admin Administrator Staff Member Forum Leader

    Your consultant is probably spot on when discussing a subject in which he/she is qualified to consult but unfortunately your "professional" is giving misinformation.

    Please refer him to this forum for support so he/she does not misinform other consumers.
  7. zach

    zach Member Forum Leader


    Attached is the document Mark Custis referred to(see page 16). Available on the internet as well.

    Your consultant is wrong. I am in year one of a pond loop (slinky style) feeding a 3T combination unit. Loops sit at a depth of 18-20 feet.

    The pond is fully iced over and has been for 2+ months in Upstate NY. The Boy Scouts and Cub Scouts had a blast augering through 10+ inches of ice to fish a few weeks ago. The bass were biting.

    16* here as I type with a gusty wind. Machine is running in stage one holding a setpoint of 70* with an EWT of 37.8*.

    I agree with the Forum Administrator, it is misinformation such as this which damages the reputation of geothermal.


    Last edited: Feb 19, 2011
  8. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    @ Phil: Thanks, I did not have enough_____to type that.

    @ zach: Ty again that is now in the new D:/ area of this new to me laptop. Learning Vista is a WIP. I am healing, what did you end up pumping the loops with?

  9. zach

    zach Member Forum Leader


    QT non-pressurized flow center with a pair of 26-99's.

    Phoenix Flow Centers


  10. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader


    I had a Wilo 35 stratos in mind. I would have to watch the watts to make a judgement. I trust Meg and the kids are well.

    Phone is still. Land line is history. email is still.


  11. mangumjs64

    mangumjs64 New Member

    Thanks for the great feedback. This is what I was looking for, a diverse group of experienced professionals. My installer has been great trying to get this system to work but I felt another opinion will help me understand my situation better.

    So let's see if I can answer all your questions.

    engineer- The loops do have a glycol mix in them, however the freeze point is not down to 15*F, if I remember correctly the temp was about 25*F. I will have to check on the dip switch.

    waterpirate- Mine was the first pond loop my installer did. His previous experience was all with wells and ground loops. He has done a couple pond loops since mine but he has used a different heat pump and the ponds do not freeze over.

    Joe- I will have to do some digging and get back on the specfics that you mention.

    Does it matter that I am trying to heat a radiant floor supply to 110*F-120*F?

    Thanks again for the help. This gives me something to work with.
  12. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    The tempurature you are looking for to feed the floors sounds very close to the max the geo can do. Is the system equiped with a buffering tank?
  13. mangumjs64

    mangumjs64 New Member

    The geo unit heats an 80 gallon tank that supplies the floor. Right now I keep the temp at 110 degrees. The pond has thawed out but the unit has shutdown several times because of low pressure.
  14. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I wonder if

    the control was set to run anti-freeze.
  15. Pond loop running too cold

    I had a pond loop running too cold in winter, and it turned out we had a loop air locked. Had to get a 6.5 HP gas pump flushing who knows how many GPM to get it to "burp" the last loop. Especially with 1.5" coils it may take a lot of flow to flush them out. I assume the coils are in parallel.
  16. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Alliedair, brings up a good point. I also found a unit that was "really" low on refrigerant this winter. It had a small leak at a service port. I now have R-22, and R-410A manifold guages in the motor home.


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