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head loss

Ken_40 Member Posts: 1,320
That are typically on their websites, stating the friction loss (head in feet) per 100' of the various diameter tubing.

For years, we used the B&G System Syzer Calculator. Head is not just length. It is also based on how many GPM's you cram through the tube. Once you know the two factors (GPM's and tube length) you can figure head losses. Of course, this sounds a bit like chasing your tail; but is the way to do it properly. If the GPM's result in re-thinking circulator dynamics, try a different model pump.

Remember, most pump curves show large swings. The ideal is to always stay within the center third of the curve. This assures the design and reality will be close. It also results in maximizing circulator efficiency/performance. One you get into the outer two-thirds, the design becomes less likely to do what's intended, both for GPM's AND Head calcs.

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  • Dan C.
    Dan C. Member Posts: 248
    calculating head loss

    When looking and a circulator curve. It says GPM on the bottom which I know how to figure out. How do you find out the head loss? For instance if i had 100 feet of 1/2" pex with no fittings how would i find the head loss?
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592

    Here a chart you can use.
  • Brad White
    Brad White Member Posts: 2,398
    Head Loss

    Not since Henry VIII has so much interest developed in this subject. :)

    The pump or rather circulator curve indeed shows performance of flow versus head or pressure required.

    As I think you are now gathering, the system head is in your domain, the circulator is the tool to be applied to the system.

    Ken and Glenn have provided thus far good bases for calculating your system head.

    Remember, you are only dealing with serving your most restrictive circuit/run, not the sum of all circuits together.

    We all hope that your circuits are equal to one-another, at least within ten percent. But if you can deliver your target flow to a 250 foot circuit, all circuits shorter than that, can be served (assuming the circulator volume meets the total too of course).

    Say your worst case circuit has a head loss of 4.5 feet plus the manifold, valves and intermediate piping seen by the circulator which may add, say, another 2.5 feet. Your 7.0 feet of head is what you are working against.

    If the sum of your flows is say, 5.2 GPM you have to find a circulator that can meet that flow at that head. Find a curve as Ken noted, where the flow and head intersect within the middle third or so.

    Remember, the curve is what the circulator will do. Change one variable (say, head) and the operating point will move along the curve (always along the curve) until it meets a corresponding flow rate. Likewise, a given circulator could deliver more or less flow if a certain head were to be imposed or not exceeded.

    More to it than that, just a brief discussion.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
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