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Plumbing plate to plate exch. to storage tank

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by JWHIII, Oct 26, 2012.

  1. JWHIII

    JWHIII New Member

    Joined:
    Oct 25, 2012
    Messages:
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    So I'm going to have to go with a plate exchanger to separate my boiler from the unpressurized storage, how should I arrange the suction and discharge in the storage tank to keep stratification ( avoid mixing)? Any ideas would be appreciated.

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  2. Welcome to the forum :)

    I don't have any ideas. I toyed with the idea using an external heat exchanger with unpressurized storage. But gave up when I finally found some propane tanks.
  3. JWHIII

    JWHIII New Member

    Joined:
    Oct 25, 2012
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    2
    The setup is:
    2 Burnham LE oil burners feeding a large shop and a house 60 feet away. Glycol in oil burners and shop/ house. Installing 60KW flex fuel boiler which will also be glycol ed. I have 600 gallon storage tank built ( unpressurized, can't afford glycol for 600 gal pressurized tank ). 60KW thats 200K BTU/h, if my math is correct, which would be 20 gpm. To stay below 4 ft/sec it would take 4ea 3/4" tubes and each would need be182' long for 50K BTU. Thats 728' of copper or about $2500........
    I would love to have coils in there to keep the tank stratified, but not at that price. Back to the drawing board.......
  4. Bob Rohr

    Bob Rohr Minister of Fire

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    SW Missouri

    If you are pumping thru a tank it pretty well mixes the temperature. With the pump off the warmer water will rise. Ideally a system to pull heat from the top and return it to the bottom when the tank is hot. With a cold tank, pull from the bottom and supply to the top. That involves more piping or a means to reverse flow.

    Remember 60KW = 204,000 BTU/ hr. Now multiply that by the efficiency, I'd suggest 80% to get 163,000 output or @16 gpm flow rate to move the energy.
  5. Nofossil

    Nofossil Moderator Emeritus

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    My $0.02:

    Not a bad idea to come in and out of the tank horizontally, and step up to a larger diameter near the intake / outlet and/or use baffles to reduce mixing.

    The heat transfer equations usually assume a smaller delta T than you'll actually have on both sides of the HX, at least until the tank gets close to 'full'. That means that you can use a much slower flow rate on both sides and still get good results. For instance, you can safely run a 40 degree rise through your boiler (140 to 180), and you could easily be drawing 140 degree or less water from the bottom of storage.

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