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Headloss thru air heat exchanger and sidearm?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by 700renegade, Feb 4, 2013.

  1. 700renegade

    700renegade Member

    Joined:
    Nov 20, 2008
    Messages:
    139
    Loc:
    NE Wisconsin
    Anyone here have a guess on headloss thru a standard water-air HX? I'm guessing mine is roughly 18" x 22" or so, 1" headers - but it feeds via 3 or 4 half inch ( or smaller ) tubes thru the coil.

    Also what about a standard 1-1/4" od copper sidearm heater?

    I assigned 50' equivalent length to my coil and 10' to the sidearm, but for some reason I'm getting only 1 or 2 gpm out of my loop from the shop to the house. It's 180' one way ( 360' round trip plus piping in basement ) of 1" pex-al-pex. According to my calcs the Grundfos Alpha should be moving 5+ gpm. I either screwed up the calcs or I have an airloc in my coil or something......

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  2. heaterman

    heaterman Minister of Fire

    Joined:
    Oct 16, 2007
    Messages:
    3,044
    Loc:
    Falmouth, Michigan
    What was the total head you figured?

    You are probably at least around 500' equivalent (maybe 20-25ft head, off the top of my head) so if everything is in series you are about at the end of the "rope" for the Alpha. It's doing all it can do and being all it can be.
  3. 700renegade

    700renegade Member

    Joined:
    Nov 20, 2008
    Messages:
    139
    Loc:
    NE Wisconsin
    My numbers with all the fittings and corrections for 40' of 1" barrier pex in my basement ( instead of pex-al-pex ), etc etc comes up to 558' of p-a-p. At 5 gpm the headloss calcs to 13.2'. Yes - right on the outer curve of a maxed out Alpha.

    Problem is it only shows 1 ( and occasionally 2 ) gpm on its display. At 2 gpm I have a headloss of only 2.65' in that system.

    I have a Taco 009 I can throw at this problem, but I'd like to know if I screwed up the calcs somehow.
  4. jebatty

    jebatty Minister of Fire

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    Jan 1, 2008
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    4,420
    Loc:
    Northern MN
    Apart from everything else that may impact the calculation, if actual inside diameter of the piping is 0.9" rather than 1", for steel pipe the head loss jumps to 22.4' at 5gpm. And at 0.95", the head loss is 17.1'. If I do the calc for pvc pipe, the head loss is even greater. Small things make a big difference
  5. 700renegade

    700renegade Member

    Joined:
    Nov 20, 2008
    Messages:
    139
    Loc:
    NE Wisconsin
    Agreed. All 1" pipe is different. 1" P-A-P is 1.032" ID, 1" barrier pex is 0.875" ID and flows roughly 1/2 the GPM as P-A-P.
    My calcs are all based on 1" P-A-P and I'm at 13.2'

    Throw in interesting tidbits like a bushing has much greater losses flowing from small to large dia ( increaser ) vs used as a reducer and all of this becomes a bit academic.
  6. ewdudley

    ewdudley Minister of Fire

    Joined:
    Nov 17, 2009
    Messages:
    1,683
    Loc:
    Cayuga County NY
    And some PEX-AL-PEX are different size as well, FostaPEX PEX-AL-PEX for one:


    Viega_FostaPEX.001.png

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