Pond loop questions

Discussion in 'Surface Water Loops' started by Toddles18, May 24, 2011.

  1. Toddles18

    Toddles18 New Member

    I'm currently building a new home and am considering installing a Geothermal Heatpump with a pond loop. In my area my loop will be primarily used for heating.

    We are planning on digging a the pond to use as the heatsink for the loop. Can you give me any guidelines as far as how large the pond should be? House is approx. 2300 sq feet plus a basement at around 1000sq feet.

    What loop design is the most efficient/best for a pond. I've seen coiled, slinky, and even a hyperloop?

    My pond is going to be around 150 feet from my home. Does each loop need run that full length and back individually, or can there be a larger supply pipe that then breaks off into the individual loops at the pond, and then back into a larger return pipe back to the house?

    Are pond loops more troublesome then horizontal ground loops?

    Do you typically frame the loop with PVC pipe to maintain spacing once the loops is sunk?

    Would burying the loop with 6-8 inches of sand in the bottom of the pond increase, decrease, or have no impact on the efficiency of the system?

    Thanks in advance!
     
  2. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    We need a manual J load on the house to size the loop system.
    IMHO the only benefit of pond loops is to tear up less yard. Since this is new construction, you have less landscaping worries.
    j
     
  3. Toddles18

    Toddles18 New Member

    The Pond gives us a couple benefits aside from the geothermal aspect. We're in need of fill dirt, so the cost of digging the pond about nullifies the cost of bringing in fill. If the pond is there it also removes the excavating costs required to dig the trenches for a more traditional horizontal loop. Having the pond I hope will also add to the overall value of the property, so those are our reasons for wanting the pond.

    Now I'm also a realist and if digging a pond large enough to work for our home isn't feasible then we'll go back to the traditional horizontal loop.

    One Geo installer I talked to said the pond should be at least as many sq feet as the house. He mentioned around a 50'x85' pond. After what I've been reading online, I'm really concerned that something that small would be adequate. I definitely don't want to have a system that doesn't provide the environment that we want.
     
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Where are you located? Climate?
    Ponds work great, I do them any day over horizontal for performance reasons, but they are not much cheaper to install. Some guidelines tell you that you need at least 1/2 acre plus at least 10 ft deep. I have done 12 ton loopfields at 1/4 of an acre 7 ft deep. So it depends. If you are in heat dominated climate, a safe bet is to spread out the pipe as a slinky. The only pond loops I have seen fail (other companies...of course!;)) if they were stacked up too much and not spread out. 150ft is fine, make sure you do a pressure drop calculation, since the longer header pipe can be a problem. Yes, one supply and one return header pipe to and from the house is fine, but again pressure drop calculation!
    House size suggests 4tons (+/- 1 ton), do a manual J heatloss. No, pondloops are not more troublesome if installed correctly, but I put in my first about 10 years ago, so ask me again in 10 years. Yes, we have used PVC to maintain spacing. No, do not cover it with Sand, the whole goal is to have water circulating around it. Most importantly, put concrete blocks or other weight on them so they don't become buoyant in case some ice forms on them. So you float them out, put concrete blocks on them (with UV resistant ties!) until they still barely float, and then you fill them, so they sink.

    Here is a link with data and pics. Temperature and Energy logging by: Web Energy Logger
     
    Last edited: May 28, 2011
  5. Toddles18

    Toddles18 New Member

    I'm located in Michigan, near the town of Frankenmuth. Thank you for answering so many of my questions!

    It sounds like calculating the pressure drop and making sure the loop is weighted down enough so it doesn't float up if ice forms are the two largest concerns.

    Thank you for sharing the pics as well.

    So I guess the only question remaining is how to size the pond to be large enough to ensure that I'll be able to pull enough heat from the ground.

    Also, how do you know how many loops and how many feet of loop you need?
     
  6. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The size of the pond depends on how much heat you need to extract during the heating season, which depends on the heatloss of your house. Without knowing how much heat the house needs, no one can tell you well how to size and design your pond loop. Get a Manual J heatloss done, that will be your starting point.
     
  7. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Had a look at the plans, even with finished bonus room load appears to be about 52MBH.
    With MI electric rates one could choose 3ton. Op cost difference$24 to $57/yr depending.
    j
     
    Last edited: Jun 1, 2011
  8. Toddles18

    Toddles18 New Member

    So, based on the load Joe has provided, what are some opinions on pond sizing?

    Thanks!
     
  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    50 x 85 feet should work. Again, while some manufactures tell you that you need at least 1/2 acre pond, I question that based on the data we are compiling with pond loops in our area.

    A usual slinky loopfield in the ground runs about 1000 sqf/ton, and given the better conductivity of water, I see no reason why 50x85 pond should not work.

    Here is what I would do: 3 loops of 0.75 pipe, 500 ft each (yes, a bit oversized, pipe itself is cheap) in a 3' diameter slinky and an 18" pitch, should give you a loopfield supporting both a 3 and a 4 ton heatpump. That would make your field about 30x63 ft. Now depth is your friend, at least 8 ft. Do not bury it in anything, just flat on the ground.
     
    Last edited: Jun 14, 2011
  10. Toddles18

    Toddles18 New Member

    Thank you so much for your opinion on size. I've been really worried that 50x85 isn't big enough. I feel much better moving forward with a plan to dig the pond now. Thanks!
     
  11. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Doc makes a lot of sense, but again depth is key, and you must make sure you have extra insurance against droughty summers for cooling.
    So if you want to economize on pond size be prepared to tax the well in a dry july.
    Joe
     
  12. ACES-Energy

    ACES-Energy Member Industry Professional Forum Leader

    Also, which is hard to calculate in the pond equation is if it is spring fed or have another source of water with constant turn over.
     

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