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Coil height in tank

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by OldStoneHouse, Apr 15, 2013.

  1. OldStoneHouse

    OldStoneHouse Member

    Joined:
    Jan 8, 2010
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    Eastern Ontario
    Looking for advice on the placement of my heat exchange coils in my tank. The dealer I bought my Innova from gave me an exchanger that he took out when he converted someone to pellets (much appreciated). The coils are about 36" high and my tank is 56" high.

    I've at least one post where it was suggested to support the coils with concrete block wrapping in poly. I was thinking regular bricks actually but I'm not sure if they will be too low. I want to protect the EPDM liner.

    Thanks!

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  2. Nofossil

    Nofossil Moderator Emeritus

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    Short answer: "It Depends".

    If the coil is used for heating the tank, it should be at the bottom. If it's used for extracting heat from the tank, it should be at the top. If you're doing both, you're in trouble.

    Here's the problem: Let's say you're doing both an you put the coil in the middle - 10" above the bottom. When you're putting heat into the tank, you'll get a nice convection loop going with warm water rising from the coil to the top of the tank, and cooler water flowing back to the level of the bottom of the coil. The water in the bottom 10" will stay relatively stationary and cold. Same problem in reverse when withdrawing heat - a layer of hot water above the coil that stays there.

    I think the answer is to put it inside a tube that is open a few inches above the bottom and ends a few inches below the top. That should create top-to-bottom circulation.
  3. Norwegian Wood

    Norwegian Wood New Member

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    Nofossil,
    Do you mean something like a 15" diameter pvc tube in which the coils sit?
  4. Nofossil

    Nofossil Moderator Emeritus

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    Something like that. Don't know if you could find a PVC tube that size or if it would hold up if you did find it, but some structure like that to force circulation around the coil to extend from the top to the bottom of the tank.
  5. Norwegian Wood

    Norwegian Wood New Member

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    Nofossil,
    I have built my unpressurized tank, and am now considering HX designs.
    It seems that most forum members have had good results with copper coil top and bottom HX designs.
    I was planning on 5 coils of 60 foot 3/4 type L for the woodgas input, and 1 coil of 60 foot for my closed loop solar collector.
    BTU extraction from storage would be 60' of tubing for pre-feed to solar DHW heater (DHW coil wrapped around solar input coil at the top 30%of the tank), and 100' output coil for baseboard HWH.
    The tube idea seems interesting for the solar loop, as the rest of the tank would be dormant during peak solar input.
    Your observations about the stratification are my question.
    Do you think it would be better to have a rectangular grid of tubing, lets say 6" off the tank floor, and another pair (DHW & HWH) at the top 6" of the tank?
    The solar could be done with your suggested tube design & would produce better results than an open tank HX.
    Do you know anyone who tried this?
    What do you think?
  6. chewy

    chewy Member

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    Pics would be awesome???!!!!
  7. OldStoneHouse

    OldStoneHouse Member

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    Thanks Nofossil,

    My coils, as they were given to me, are 30" wide so it's going to difficult to find a tube that large! I've got 3, 100' foot coils of 3/4" copper plus 100' of 1/2" copper for DHW.

    So what would be a solution to the problem be - put the coils at the top and then use a pump to circulate when loading - or the opposite arrangement and run when extracting?
  8. Nofossil

    Nofossil Moderator Emeritus

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    If you're making your own coils, make them full height and choose the flow direction based on use - bottom-to-top for extracting and top-to-bottom for charging. My impression is that the OP had a smaller (and perhaps finned) coil. If such a coil is to be used for both charging and extracting, it needs to be in a vertical 'pipe' to promote complete circulation in the tank.
  9. Norwegian Wood

    Norwegian Wood New Member

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    Here's a couple pix.
    I'll post the whole thing when I'm done, or along the way.
    $1500 worth of wood, screws, bolts, and insulation, and I'm still not done.
    Never mind the co$t of copper HX's.
    At least I'll be able to say, "No more #2".

    Attached Files:

  10. chewy

    chewy Member

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    Looks good!! How many gallons will it hold? How hot do you think you can get the tank? Keep us posted.

    Erin
  11. Norwegian Wood

    Norwegian Wood New Member

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    This is 1000 gallons.
    As to how hot it will get, we'll see.
    Do you really have 15,000 gallons of storage???
  12. chewy

    chewy Member

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    No, nothing in my signature is true!!! It was a continuation of mikefrommaine's April fools joke! I would check out my vid if you want to see a real setup!!

    Erin
  13. kopeck

    kopeck Minister of Fire

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    With my tank the coil goes from top to bottom and is used for both charging the tank and pulling heat out.

    Works pretty well.

    K
  14. Brialin

    Brialin Member

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    I like your tank. Mine looks about the same. It is 12' long and 4.5' wide. One side is against the foundation. When I first filled the tank it bowed out almost 3" in the
    middle. Looked kind of scarey,1000 gallons in the cellar what a mess that could be. I emptied out the tank and wrapped it with two bands of 4" channel iron all welded in place. Feel a lot better now but the tank still bows out an inch in the middle. Tank is 12 years old. Had to replace epdm liner once.
  15. mole

    mole Member

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    Can you add some length to the coils? If they're 100' long, maybe you could add another 20" of height by adding another 50' of so to each coil? You're only looking at sweating a couple of connections. Another possiblility might be to simply stectch the coils taller, like an accordian. I don't know what kind of support holds the coils to height, but could you remove the supports, strectch the length, and then put in new supports? I made my coils from two 60' lengths of 3/4" type L tubing soldered together. Then I pulled the coils out to the height I wanted and twisted/wrapped copper wire supports on the sides to prevent the coils from collapsing.
  16. Norwegian Wood

    Norwegian Wood New Member

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    I'll add some new pix as I progress, but I wrapped this box with a lagged 4X6 & 2 4X4's as well.
    I'll put in a couple galvanized steel straps at the top to tie the long sides together when I'm done.
    Did you do this?
    You have me worried.
    Thought I built this like a brick chit house.
  17. OldStoneHouse

    OldStoneHouse Member

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    Stretching is a good idea - I'll have to see if I can make it happen. Right now the supports are 3/4 copper that is tied to the coils but I need to take them off to get the coils in the tank anyway. I'll post some pics once I get going.
  18. Nofossil

    Nofossil Moderator Emeritus

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    I used three pieces of 1/2" rigid copper as legs and vertical supports for my coils. I tied the coils to the legs with 12 gauge solid copper wire and soldered them once everything was straight. I stood the legs in PVC end caps to avoid metal-to-metal contact with the tank.

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