New Construction - looking at geothermal using pond loop

Discussion in 'Surface Water Loops' started by niteseer, Nov 21, 2014.

  1. niteseer

    niteseer New Member

    Hi Guys
    Geothermal newby here. I'm going to build a new 2400 SF home ~30 minutes north of Raleigh, NC. Mild winters w/very little snow but hot, humid summers. The home will be <200 ft from a 1 1/2 acre pond running 14-18' deep in the center with moderate flow thru-out the year. The house will have a basement and the walls will be 2x6 w/fiberglass batten but foam in the roof.
    I've found some Geothermal contractors in the area but not many I feel confident in. I know enough that lowest price is not my deciding factor. I want someone who knows what they are doing. I've found one: Louis Heating and Cooling owned by Tom Paonessa who has been putting in geothermal systems since the 1980's and seems very knowledgeable. I'm meeting him at a job-site next week to see an ongoing project.

    After describing my situation on the phone, he, sight unseen, gave me a quote of ~$29,000 to do the project start to finish. He stated up front not to hold him on that as he said he wanted to get up front the type of costs I was looking at. He deals w/ClimateMaster equipment. He spoke further about creating 2 zones (Master BR / rest of house). He estimated 3 1/2-4 tons. Stated 3 coils would probably do but he would rather go 4. Coiled loops w/antifreeze solution would be sunk into the pond on a frame to keep it clear of the bottom so sediment would not cover.

    I was curious of everybody's take on the above conversation. I admit it is very preliminary with not a lot of detailed info. I will speak to him about a site visit during which he may be able to give me more details. I would really like to know what questions I need to be asking.

    Thanks for your input
    NiteSeer
     
  2. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Hello, and welcome.

    I do pond loops. I do not get the issue with the loops silting into the bottom of the pond. When the loops get silted in and/or slimed with algae, are they any less in contact with water? I do not think so.

    From the birth of a pond, Mother Nature is going to try and make the pond into a wood land. She will do it. Why fight MN?

    At the very best you will have very deeply buried set of loops. The loops will be in soil that likes water, so they will work very well.

    The loops in my photo are now six years old. They are not yet silted in enough for the cat fish not to use them to steal bate and tackle. They provide 41* EWT with 12" of ice in the pond. They are not in the deepest section.

    My point is not to send the money to try and prevent what MN will do.

    Mark
    lake-erie-indoor-air-services.net
    440.223.0840
     
    Last edited: Nov 24, 2014
  3. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    All sounds good so far. Good approach from the contractor. keep us updated.
     
  4. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Doc:

    The silt does not matter.

    Why spend the money?

    Mark
     
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    I disagree. The reason why pond loops work very great in heating mode is stratification. 39F at the bottom of the pond, loops take heat out, the colder water becomes lighter and lifts up, warmer water flows to the pipes, replaces the colder water. If the pipes get buried in silt, you do not have the heat brought in through the flow of water, just by conduction through the water in the silt. Very good conduction, but less than free flowing water!
     
  6. heatoldhome

    heatoldhome Geo Student Forum Leader

    Edit. Someone else posted under my name.
     
    Last edited: Nov 29, 2014
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Heat goes to cold as much as cold goes to heat. It is called heat exchange.
    Of course ground loops work, since heat is brought in via conduction, as outlined above. However, water is a unique element since it has its it highest density not at freeze point but 7F above freeze point (39F). That is why the bottom of the pond is alway 39 F in the winter, where the heaviest water is. If heat is extracted from the 39F water via the pipes, the now colder (and lighter) water rises up and warmer water (39F) replaces it. The top of the pond usually has the coldest water (32F) which then freezes. Thus the pipes on the bottom always have a constant flow of warmer 39F water to them and colder water away from them. If the pipes now get buried in silt, you need more pipe since the flow of warmer water to the pipes is interfered with. It will essentially act like a very good ground loop, very good since it is saturated with water which is a great conductor of heat.
    But it will never work as well and have as much heat to draw from as a pond loop with stratification flow around it.

    http://ohioline.osu.edu/a-fact/0007.html
     
  8. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    First thing. The post just above the above post by doc was made by me. How I got logged in as Heatoldhouse, I do not know. I tried to delete it but did not delete.

    Doc, what is silt?

    How can the silt impeach the heat transfer?

    Tell me the 1st law of thermal dynamics.

    Heat transfer is not a two way street.

    Mark
     
  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Silt definition: earthy matter, fine sand, or the like carried by moving or running water and deposited as a sediment. May also exist as soil deposited at the bottom of a water body.

    Silt can impeach heat transfer compared to water flowing freely around the pipe.

    "The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems. The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed. "
    By definition, if you transfer heat from one medium to another, you also transfer coolness the other way.
     
  10. niteseer

    niteseer New Member

    Hi Guys,

    Don't want you to think I've forgotten my original post. I keep checking back to see the replies and general conversation. A question I've had is everything I read keeps telling me the 'pond loop' is the most economical to install of the various methods used. However, the contractor I mentioned above tells me its all about the same. (Even the brochure of the company's equipment he uses tells me a pond loop is the most economical to install.) I understand that on-site conditions differ, but, generally speaking, what's the deal? Assume the same site with fairly ideal conditions, body of water that meets requirements, plenty of acreage, etc. are all the generally used methods approximately equal in cost? Would there be (should there be) a substantial difference in installation costs? BTW I haven't met with him yet as he was very busy just before the holidays. I hope to break ground by the end of January but depends on my builder's schedule.

    Thanks
     
  11. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Verticals are the most expensive, directional boring second and horizontal/pond least expensive in my AO. Pond loops require less digging and less pipe so perhaps they should be a little less expensive however, distance to the pond could consume any savings in digging. Remember too that digging is the smallest cost of the loop system and is still required on evey loop system.
     
  12. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Pond loops close to the house are about $1000 less then horizontal loops.

    They also work the best in the north, since the bottom of the pond does not get below 39F. But they run warmer and less efficient in the summer. But if A/C/ is 10% of the annual energy consumption. In NC it might be different. Also by the time you run 200-250 ft (out to the middle of the pond) you probably have your loop field built. In addition it is a lot of pumping power to go 2x250 ft with the header pipe. So the horizontal loop field might be the best combination of operating expenses (loop performance and pumping power) and installation costs. But it all depends on your loads, and your contractor.
     
  13. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Pond loops are also more vulnerable to damage and droughts can reduce capacity if lake levels drop. We had a 16 ton system where record temperatures and a drought made it nearly inoperable.
     
  14. niteseer

    niteseer New Member

    Hi everyone,

    I want to thank all for their replies. As I said, I keep checking back. So here is an update and a few more questions.
    Update: Still haven't broken ground. All the rain has put my builder and his crews behind schedule on most of his projects. Also, I've had to wrangle with my inspector on where to place the septic field but finally have that resolved.

    I have spoken to a contractor who has done many installations and he left me with a few questions.
    1st - Here is the scene again - I have plenty of ground surface acreage (10+acres), the edge of my 1.5 acre pond is 110' from my house and the deepest section (14-18') is ~40' from the edge so call it ~150 from the deepest part of my pond to the house. I've decided my home will have,brick exterior, good quality double pane windows/doors, 2x4 batten in the walls and foam in the roof deck. I know you can't define a thermal load from this, but I just wanted to give an idea what you are looking at. My builder and most people I've spoken to say the house will likely need between 3 to 4 ton heating/cooling. Remember, I live in central NC where average temps in winter are ~32 degrees but summers run 90-95 w/high humidity.

    The 1st contractor I spoke with states the pond loop is not as efficient as a ground loop and that if I went that route, he would want to install a backup electric heating system in my home for winter heating. He also didn't like a horizontal loop and strongly suggested vertical. He didn't really offer any strong arguments against the horizontal but simply seemed to favor the vertical because that is mostly what he has done(he would sub-contract out the drilling).

    This doesn't jive with what I've learned about most loop systems. All things being relative, the least to most expensive run: pond loop, horizontal then vertical loop being the most expensive. Given the information I've provided about my pond and distance from the home and assuming I have an ideal area for vertical or horizontal ground loop:
    1) Which is the most efficient loop system? (Water is an excellent heat-transfer medium, so does that make the pond loop the most efficient and, therefore, the better choice when available?)
    2) In the climate I've described, would any of the choices require some type of backup heating in winter? (from what I've learned, I would say the answer is no)
    2) Which choice best fits the scenario I've given for a home in central NC or are they all equal with cost being the deciding factor?

    I'm not asking anyone to make the choice for me as I'm on the ground and that final decision must be mine, but I will use your answers to guide me when I speak to other contractors in my area.

    Thanks to all for your response.
     
  15. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Again, pond loops are mostly efficient for heating purposes, since the water at the bottom of the pond will never be below the upper 30s. Why that would be the reason for a backup is a mystery to me. We always put in an electric heat element, to make the unit smaller and more efficient, and to be there in case of a mechanical failure.
    Horizontal loops are fine too, in my opinion superior to vertical in terms of performance.
    1) Pond>horizontal>vertical
    1) b) Cost: Pond>horizontal>vertical
    2) back up heat is mostly for a piece of mind, it is cheap to install. Supplement heat can be a smart design choice, allowing for a smaller unit which can more efficient over the year. There is lesser of a place for supplemental heat with the newer variable speed heat pumps.
    3) see 1) b)

    You contractor seems not to understand the different loop choices well.
     
  16. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Why would you possibly need 4 tons for heating on a 2400 SF house uin NC? What is the heating/cooling load.
     

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