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Closely spaced tees

KCA_2
KCA_2 Member Posts: 308
in Radiant Heating
Why is the set of closely spaced tees in a P\S system considered the point of no pressure change for that secondary?



  :-)  Thanks
:-) Ken

Comments

  • Ironman
    Ironman Member Posts: 7,510
    Because...

    When the expansion tank is in the primary, the secondary "sees" the entire primary as the PONPC.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • KCA_2
    KCA_2 Member Posts: 308
    What if the

    expansion tank is in the secondary?  Then the primary sees the tees as the PONPC?  Would make sense...
    :-) Ken
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    expansion tank is in the secondary?

    I have a W-M ultra 3. In the installation manual they give examples of how to pipe the things. All of them have the  expansion tank and the air eliminator in the secondary loop (the one the boiler is not in).



    I do not know if it matters much where the expansion tank is located, but it seems to me that it would be better to have the air eliminator in the primary (boiler) loop that sometimes runs on a higher temperature than the secondary loop ever does. (Domestic indirect is connected in the primary loop.)
  • Ironman
    Ironman Member Posts: 7,510
    Terminology Again

    JDB,



    I think we're using the term "primary loop" differently again. You are using it to refer to the boiler loop; I was using it to refer to the main loop into which the boiler injects and the zones extract. I know there are several variations, but this seems to be the most common setup.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Terminology does not matter in this case.

    If there are two loops sharing the closely separated Ts, then whichever loop has the expansion tank in it, the other loop sees the Ts as the point of no pressure change, right?



    I was not disagreeing with your post anyway. In fact, I agree no matter which loop the boiler is in. What matters is what loop the expansion tank is in. Right?



    I was really responding to KCA, and remarking that my boiler is piped according to manufacturer's specification, with the expansion tank in what I call the secondary loop. This is the way I think KCA was asking about. I call the loop with the boiler in it the primary loop. And perhaps you call things the other way, and there is no problem as long as we make it clear. In this case I do not think it matters. I try to call the loop with the boiler in it the boiler loop, and the loop (or loops, if the system is piped that way) th load loop, but I forget a lot.
  • Ironman
    Ironman Member Posts: 7,510
    Understood

    I know you were not disagreeing with me. I was just trying to point out that we were identifying the loops differently and offering some clarity as to what I meant. :)
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • KCA_2
    KCA_2 Member Posts: 308
    edited February 2012
    Your calling it

    The way I do Jean...  The Boiler loop or what I call the Primary...  And the system loop or what I call the secondary is where the expansion tank & water makeup is...  Strange way of doing things ....  I always put the ex tank & eliminator in the primary...  But the reason for this post was that  I still have a bit of pressure creep and need to figure out where it's coming from...  Just looking for ideas....



    ...  :-)   Thanks
    :-) Ken
  • JEHeat
    JEHeat Member Posts: 1
    Primary & Secondary Loops

    When using a primary & secondary loop on the primary loop is the circulator on the supply or return of the boiler?  Where is the expansion tank placed, is it before or after the primary loop, on the secondary loop?
  • KCA_2
    KCA_2 Member Posts: 308
    Hey Brother

    You need to read "Pumping Away"....  Great book by Dan and available right here on this site..



      That being said...  The primary loops can be so short that it's hard to say if the circ is on the supply or return...  But I install it on the supply and pumping away from the expansion tank....The idea is that if you install the circ on the return pumping into the boiler then with a big pump. you can blow off the pressure relief valve.... 



      Hope that it helps



      :-)  KCA
    :-) Ken
  • Gordy
    Gordy Member Posts: 9,546
    edited September 2012
    Primary secondary

    The x tank, and air separator should be in the primary (boiler loop) with the primary circ pumping away from the x tank at the supply side of the boiler.This helps facilitate better air removal due to the hotter supply water off the boiler. The secondary circs should pump away from the closely spaced T's of the primary loop. Sometimes there is not enough room to install everything at the boiler proximity. So if the x tank, and air separator are installed in the fore mentioned secondary loop it becomes the primary loop. Same pumping away rules apply for the circ locations. So the secondary circ location which would have been the primary loop should still be located on the supply side of the boiler.Gordy
  • JStar
    JStar Member Posts: 2,752
    The original topic.

    Back on track for an answer to the original question.



    What defines the pressure in a system? The expansion tank. So, the tank will determine the pressure inside of the closely spaced tees. The tees will not affect any other pressure in the system, so they act as a secondary point of no pressure change. Think of it as a reference/bookmark for the expansion tank. Even if there is no expansion tank, the tees will not have any affect on the system pressure, and thus become the PONPC.



    The tank sets pressure. The closely spaced tees will not affect pressure. Different concepts. Similar results.
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