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Dhw primary pump positioning choice

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Teemok
Teemok Member, Email Confirmation Posts: 511
I was taught to pump towards the highest head. A DHW pump in a parallel primary arrangement for an indirect has to move water through both the boiler and indirect coil. If the coil has higher head than the boiler than the pump logically goes on the supply pumping to the tank coil. The CH Primary will be pushing to the boiler.
It's easier to understand and tidier if both the pumps push the same way. Lochinvar has them both pushing at the boiler. Also the return is often piped lower and is less likely to have to deal with air and is a bit cooler.
I've seen drawing both ways
Is it 6 or 1/2 a dozen? Any wisdom or logic on it?

Comments

  • hot_rod
    hot_rod Member Posts: 22,271
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    The PONPC is the key to delta P, dynamic pressure 
    This article does a good job of explaining it.

    Notice how a small change in the location of the expansion tank changes the dynamics pressure profile 

    Who was it that taught you to pump at the highest pressure drop? Was PONPC concept in the teaching?🥴

    https://www.pmmag.com/articles/83943-picturing-p-br-john-siegenthaler-pe
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Teemok
    Teemok Member, Email Confirmation Posts: 511
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    Where to place the expansion tank and air sep. has little to do with it if the pump in question is not in that loop. PONPC was not taught to me young. I had to read about it in a handy little book I found at when I was 21 or so. So good. The reasoning for pumping to the highest head makes no sense to me in that its a hydraulic loop. Unquestioned principle I guess. Something about where the high and low pressure zones are created. Maybe it's from well and pressure pump wisdom. You don't want to have too low a suction pressure or you'll get cavitation or suction leaks or how it stress loads the impeller. If it made clear sense to me I wouldn't have asked. I see manufactures push into boilers keeping pressure switches happy and maybe other things.
  • hot_rod
    hot_rod Member Posts: 22,271
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    in a closed loop hydronic system all the circs reference the expansion tank, unless they get completely valved off somehow. 

    It gets complicated when you have multiple, or many circs. Complicated piping like a combination p/s with parallel circuits and circs on returns really create a head scratcher, as far where to locate the expansion tank connection for best results 

    Knowing the pressure drop of the various circuits allows you to graph the pressure profile, as that article shows

    Circulators cause fluid to move by creating a pressure differential

    How and where that differential is obtained is directly related to the PONPC

    Pumping Away by Dan explains this best

    Siggys article shows a very common piping arrangement and  how the exp tank works for or against you, regarding dynamic pressure 
    Did you read it?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Teemok
  • Teemok
    Teemok Member, Email Confirmation Posts: 511
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    The drawings wouldn't expand but I got .Yes, I see. Straightening the diagram out makes it clear. Dan's book was the handy little book I referred to. Thanks. It's been a while since I tested that understanding. I'll refresh.
  • Teemok
    Teemok Member, Email Confirmation Posts: 511
    edited September 2023
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    I realize I may have been calling the boiler loop the primary loop incorrectly many times. I had it in my head that the primary was defined by heat flow from hot to cooler or the other way around for chilling. I should call the distribution circuit the primary if it has the expansion tank and fill point. The boiler circuit is A secondary circuit not the secondary. Other close T circuits off the primary are secondary's as well.
  • hot_rod
    hot_rod Member Posts: 22,271
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    There can only be one primary loop. Any other connection via closely spaced tees is secondary. Some times you have trietrtay loops, injection mixing for example.

    Its possible to have parallel loops off a primary loop, with a dedicated circulator. Indirect tanks are often piped as parallel loops. This way you flow directly from boiler to tank without any blending through tees or hydro seps

    If you have a-primary loop with its own pump, and loads are taken off with sets of closely spaced tees, that is a series primary loop

    If you want the same temperature in each secondary, a parallel primary loop is best

    confusing enough?




    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Teemok
    Teemok Member, Email Confirmation Posts: 511
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    No not that confusing. I'm up on the piping variants, advantages and disadvantages. Logic for labeling terminology was off and NONPC skills are faded from doing cookie cutter residential and follow the diagram installs and annual services of good working systems. If it was easy, everyone would be doing it.