Plumbing plate to plate exch. to storage tank

JWHIII Posted By JWHIII, Oct 26, 2012 at 1:02 PM



    Oct 25, 2012
    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.
  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.


    Oct 25, 2012
    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

    Jan 9, 2008
    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

    Moderator Emeritus

    Oct 4, 2007
    Addison County, Vermont
    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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