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pressure drop

Bryan_16 Member Posts: 262
do I determine the ft hd with a system piped parallel reverse return? Supply leaves boiler room and tees to 2 different circuits. Am replacing zone valves with pumps and need to figure pressure drop through system to size pumps.


  • Ken_8
    Ken_8 Member Posts: 1,640
    You need to know...

    if all zones are 2-P,RR?

    If so, you need to know the approx. pressure drop across each emitter (radiator, fan coil unit, HWBB, etc.

    Then the length of the entire longest circuit.

    The pipe diameter of the trunk and branches.

    Then the output in BTU's of each emitter at design temp.

    And then you need a table or B&G whiz wheel to imnterpolate those parameters.

    If you have a fax machine, or email - I can send you the ASHRAE (I=B=R) table.

    The basic number of a 20° dT is pretty much the correct drop in any loop.

    Good luck

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  • Weezbo
    Weezbo Member Posts: 6,232
    This is important enough not to let it fade into oblivion.

  • Bryan_16
    Bryan_16 Member Posts: 262

    "2-P, RR" what does the mean. I figured P=parallel and RR=reverse return. What does 2 mean. I have all lenghts, diameters and pressure brop through BB. All the circuits per zone are the same lenght with the reverse return, correct? Also have B&G System Syzer, would ASHRAE table help me? Thanks for the help.
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