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Storage Tank Stratification

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by George Webster, Nov 4, 2012.

  1. George Webster

    George Webster New Member

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    I have an Attack DP356 Profi to which I plan to connect an 800 gallon tank. This is a milk bulk storage tank I got for free, which looks like a small milk truck - the tank runs horizontally. It's about 5' tall and 8' long. I'd like to get the best stratification I can and would also like to make sure I size the FPHX properly. My thoughts for the tank are to install a supply and return header in the tank, return at 6" or so from the bottom and the supply about a foot or so from the top. These will be constructed of 1" CPVC. The headers will run horizontally end to end in the tank. Each header will have a series of 3/4" holes, the return at the bottom will have holes facing down, the supply at the top will have holes facing up. I am hoping this will reduce turbulence in the tank and promote stratification. For the FPHX, I plan to use a 700KBTUH model, to ensure I can achieve a fairly low approach temp and fully charge the tank. This will be connected at the boiler with 1" black iron and a Taco 3 speed circulator. At the tank side, there will be two Taco 007's, one for each direction, with 1" pex. Any thoughts on the manifold idea and FPHX size?

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  2. Clarkbug

    Clarkbug Minister of Fire

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    Hi George, and welcome to Hearth!

    I may be wrong, but I thought CPVC was only good to 180 degrees for some reason... I would be leery of making a manifold with it unless you can support it properly at both ends. Even then, drilling 3/4" holes in a 1" pipe seems like you are really going to be removing a lot of the "meat" of the pipe. I doubt you will have much flow by the time you get to the end of the run... What about supplying at the top at one end and returning at the bottom on the other end? That would certainly help avoid any short cycling. I believe that there are others here who have used bulk tanks for storage that can provide some better input.

    Also, not sure how many BTU's the attack is rated for, but the 1" piping might be a little small. I have a boiler that peaks at 140kBTU or so, and I went with 1 1/4" piping.
  3. jebatty

    jebatty Minister of Fire

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    As to CPVC headers, probably OK if supported as there really will be no pressure. At the same time, I doubt that you need so much effort to get good stratification. My 100 gal LP tank is 3' diameter, similar supply/return locations, Taco 007, and excellent stratification. The stratification issue though has not to much to do with the supply/return headers but rather the temp of the return water. That temp certainly will be the "bottom" tank temperature.

    This alone doesn't mean much because the btuh rating relates to Side A gpm, Side B gpm, delta-T Sides A and B, approach temperature, and related to gpm's the pressure drop in Sides A and B. From this info you can determine whether the hx will do the job you want it to do. Your post shows that you have given this thought and hopefully have all of this figured out, but be sure you do so. If you have used the flat plate software or similar, then you are on the right path.
  4. maple1

    maple1 Minister of Fire

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    My two horizontal stacked tanks are a pretty simple layout. Supply in at top and return out at bottom of same end, and a connection at other end from bottom of top tank to top of bottom tank. It stratifies good - I don't think it would be worth all the bother of doing the header thing. I'd just go in & out of opposite points as Clarkbug mentioned.
  5. Robby

    Robby Member

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    I use a 54" x 11' (domed ends) tank, 1200 US gallons. To boiler out bottom, from boiler to top. 80F to 90F stratification daily. In another thread I asked about different temperature measuring methods on outside of tank to determine where the actual line is.
  6. BoilerMan

    BoilerMan Minister of Fire

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    Welcome, you may be the only other Attack user on here, unless someone else buys one. 1-1/4 will serve you better, can't speak of the CPVC, I've seen it get brittle and crack when exposed to higher temps for prolonged times.

    TS
  7. George Webster

    George Webster New Member

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    How do you run your lines in and out of the tank? Just a simple pipe, dead ended into the tank?
  8. George Webster

    George Webster New Member

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    I don't know of 1-1/4 pex and anything else is prohibitively expensive. I am a bit concerned about what happens during tank charging, when it is the only heat demand. I do want to extract everything the boiler can put out. The lines are one thing you can't go back and change simply if it doesn't work out.
  9. Robby

    Robby Member

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    I have a real simple system. Boiler pipes just simple reducer to 1" copper out and in to tank. Heat to house same thing on top fitting (hot water out to house) and return line (from house) is about 9" up into tank. House heat is hot out one end, return back in other, same for boiler. Not sure why, house (9 zones) can run as often and as many as needed and does not upset stratification. I assume the flow is low enough. When boiler to tank pump runs stratification is less. Because I only measure temperature at top and bottom of tank it is difficult to tell exactly how much, a problem I intend to rectify. Every time I get tempted to get to fancy I remind myself KISS.
  10. George Webster

    George Webster New Member

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    The only software I could find didn't seem to work, no matter what I put in. It kept telling me I had to not put in certain parameters (so you have to wnder why they are there), but no matter what combination I tried, I got nothing out. Can you point me to something that works?
  11. George Webster

    George Webster New Member

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    OK, so what you're saying is the pipes simply extend down from the top of the tank, with an open end facing the bottom of the tank? This was my initial thought until my neighbor (nofossil) got involved and got me all worried about stratification. I am thinking about going much simpler, but also making sure I have good service access to my tank. Probably a hinged roof. I can always make it more complicated next season if the simplest approach doesn't work. I'm now considering a simple 1" copper line extending straight down into the tank, with maybe an elbow on the end to direct the flow horizontally. Return at one end near the bottom, supply at the top at the other end of the tank. From the responses I've gotten to this post so far, that seems the most sensible. One thing that seems common herre is no one appears to believe that a lot of complexity will make the slightest bit of difference. What about a stratification tube? I've read a bit about those too and they seem interesting, although a bit complex to build.

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