Lake loops

Discussion in 'General Discussions' started by meyricl, Sep 9, 2008.

  1. meyricl

    meyricl New Member

    I have a client who would like to use a lake in a large comercial geothermal application, does anyone have any rules of thumb or experience.
    The only thing I have had any experience with has been some smaller residential installation where we used one acre of surface area per ton of equipment and 450 ft of 3/4" coiled pipe with a 1" spacer between the coils
    Any advice would be appreciated:confused::confused::confused:
     
  2. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Not sure about a rule of thumb for this. My commercial loop design program can calculate the lake loop for you.
     
  3. CapeGeo

    CapeGeo New Member

    For a Large Geo Apllication I would go to an open system and use the Lake water. One intake deep in the lake 20 ft. or more, Filter it and run it thru the unit. Discharge it back to the lake. May want to use some of it for Landspace watering or flushing the toilets. Open systems have high cop's. The cost of putting loops with antifreezer in the lake could be a problem with local goverment.
     
  4. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    An open lake water system would have a lot of maintenance issues. I would not recommend one.
     
  5. CapeGeo

    CapeGeo New Member

    Open Loops are used all the time. It could be wells for ground water or a body of water. Lake, Ocean ect.. The question was a Large Commercail customer. This would mean a 50 ton system or bigger. A customer this size would have a maintence staff to clean filters and back wash the system.
    Example Hotel in Boston Ma. Using seawater from the habor. 10 10ton systems.
    If closded loop used would be over 10 miles of pipe.
    Woods Hole cape cod
    6 heatpumps Using wells. Web site
    WHRC Building Performance: Energy Flow
    Gives a live update on it's energy usage. Good site to look at.
    About half or more of the geo system in New England are open loops.
     
  6. meyricl

    meyricl New Member

    This is going to be a closed loop system. In my research I have found recommedation for 300-400 ft of 3/4" pipe per ton and 1-3 acres per ton of equipment, the depth should be 8-12 above the top of the pipes and the pipes should be at least 1 foot off of the bottom of the lake
     
  7. TedK

    TedK New Member

    There simply are no rules of thumb - a lot would depend on water temps which depends on depths and latitude, sun exposure etc. More unstable than ground temperatures. I would involve a registered P.Eng to supervise and in the end sign off on the design, including stamping the drawings and heat loss calculations. Get it right and cover yourself in the event of future issues. And form a relationship with an engineer.

    My apologies if it sounds like I'm accusing, that's not my intention. "Winging it" - which I don't think you're intending to do here - damages the entire industry and should be avoided at all costs. I think winging it is the bane of the geo industry and always has been.
     
  8. I fully agree with Ted. You can get ballpark, rough order of magnitude (ROM) numbers based on "rules of thumb" but, like any geothermal system, a lake-loop design needs careful engineering and design. My company Lake Energy Systems, specializes in lake-loop systems because they are more cost effective and have a faster ROI than earth loop systems. We would be please to look at your application and submit a proposal. Please visit our website at www.LakeEnergySystems.com or you can contact me directly. at "paul@lLakeEnergySystems.com"
    914.600.5555
     
  9. Geotech

    Geotech Member

    salt water

    Capegeo what kind of heatexchanger are being use for salt water from talking to others titanium is the only material that will stand up to salt water?
     
  10. arkieoscar

    arkieoscar Member

    On our offshore drilling rigs we used tube-in-shell exchangers, cast iron shells with copper alloy tubes. Some had been in service for over 12 yrs. when I retired. Maintenance depended on the quality of the water where the rig was working at the time but was never a real problem. I'm using a titanium exchanger that we were going to try on a rig in the Arabian Gulf in the 80's but never got to use because the rig was shot up during the Iran/Iraq war. It's way overkill (was for a 10 ton unit) for my system but has been trouble free for 13 yrs. on my closed loop system.
     
  11. How did you arrive at 1-3 acres per ton? I have heard others quote similar acreage, but disagree. We reccomend a minimum of a 1/2 acre lake with a a minmum depth of 10'. The math is pretty basic and I can lay it out for you if you'd like. Also laying the loop directly on the bottom gives you the most stable temps. Water is most dense at 39.2 deg and will fall to the bottom, be warmed by the earth and rise again. A frozen lake/pond is also better in winter because the ice provides insulation.
     
  12. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I agree with Lake

    I size for pond loops by what the machine wants to see at 32* EWT, and my trusty "System Sizer".

    I also sink them to the bottom. If they silt in who cares.
     
  13. Hi Mark. New to this forum, so I hope I'm doint this right. Thanks for the reply. What's a "Systems Sizer"??
     
  14. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Hello, and welcome

    I am a forced air guy first. Started playing with geo in the mid-'70s.

    I got into heatinghelp.com, and convered to being a wethead.

    The system sizer is a wheel type slide rule that tells all about moving BTUH with pumps and liquid. It was designed by the late great Gil Carlson, who was an engineer with Bell & Gossett. I use the wheel, but it may be on line as a down load.

    I feel most of the problems discussed here about short looping could have been prevented if designers thought in flow instead of feet of pipe.

    Water to water geo with radiant and chilled water F/A is my favorite.
     
  15. Well, you're way ahead of me, I'm very new to Geo. I'm an engineer and a math head, so all of the calcs associated with designing an efficient geo system come pretty naturally to me. I agree that most of the problems come from poor system design, both flow and length. I see numbers all over the place - like 1-3 acres of lake per ton of cpacity?? I'm at the helm of a geo energy startup (www.LakeEnergySystems.com )and could learn a lot from someone like you with decades of experience. Thanks for your inputs.
     
  16. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    That link didn't work for me just now

    server down?
     
  17. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Thanks for the look

    We all are here to learn.

    Have tools, do travel.
     
  18. zach

    zach Member Forum Leader

    pond freeze

    Mark

    We've talked before off-line but thought I would post this for all to learn from:

    I have a pond 170' long by about, on average, 50' wide. About two weeks ago I went on the ice with my chainsaw and cut six test holes. The ice averaged about 15" thick.

    In an area about 50-60 feet by 40 feet I was getting consistent water depths of 8.75 feet. The pond is both spring and surface fed and has absolutely never gone dry (or close) in over 40 years.

    I have had two contractors tell me they are concerned with a using the pond due to the possiblity of freezing it completely in the winter.


    Both contractors agree I am looking at a 3-4 ton system.

    The install you show via photograph: Northeast Ohio? Pond depth? Pond size? Freeze issues?

    Thanks, you have been very helpful. This forum is great.

    Kevin
     
  19. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Some math

    Consider your tub of water 55 x 40 x 7.5 (8.75'- the 15" already frozen)

    It weighs right at 1 million pounds (actually 1,031,250 lbs, but who is counting).

    Reducing it from ~35 F (likely average temp from bottom to right below ice near top) to 32 F and then freeze it entirely would happen upon extraction of right at 150 Million BTU

    A nominal 4 ton unit might extract 27,000 Btuh in high stage with EWT of 30. At that rate unit could run 5555 hours (231.5 days) before freezing the entire pond. That won't happen in the course of a typical winter.

    But yes, significant ice would likely build up, starting at the pond loop tubes.

    Earlier discussions here suggest that might be OK in terms of conductivity and heat transfer, but I'm not at all sure typical pond loop design contemplates the loop tubes freezing much of the pond right near them.

    I live in Florida - ice does not exist in the wild here - only in captivity.
     

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