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Measuring flow in a hydronic system

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Comments

  • lkstdl
    lkstdl Member Posts: 45

    @jumper That's a good method when we know the curve. In my case many of the zones don't have a published curve (e.g. arbitrary amounts of PEX in a slab, with multiple loops that are approximately but not exactly equal).

    What are people using for differential pressure measurement? I'm familiar with the one from Grundfos but haven't tried any of the cheap ones on Amazon.

    Luke Stodola
    DCContrarian
  • hot_rod
    hot_rod Member Posts: 23,278
    edited September 30

    a good quality 15 psi gauge is all you need, valve it to both sides of the pump

    PT ports allow you to check temperature and pressure, so you come up with all the actual data, GPM from the pump curve, delta T from actual temperature readings.

    You need to run until thermal equilibrium is reached, steady state operation, then read the temperature delta.

    A refrigeration manifold works also to valve either side. This example shows the pressure differential on a small circ.

    The next Caleffi Idronics will detail how this device works. Remove the pump, insert this assemble to measure and define any circuit

    This helps determine the ability to use a HP in a retrofit, by measuring the circuit as it exists

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 23,278

    A PT port with a pressure

    gauge connected to the “needle”

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • DCContrarian
    DCContrarian Member Posts: 667

    Just to clarify the question, this is for a floor radiant heat system. I know the total system flow and heat output, I'm trying to figure out a way to calculate the heat output of each zone.

  • RPK
    RPK Member Posts: 119

    This is a great method and good way to get a reality check if a balancing valve reading seems questionable. Just need a pressure drop and corresponding flow. Can be misleading if the device is fouled/plugged though.

  • fentonc
    fentonc Member Posts: 278

    Do you know what the nominal output is at a given temperature? Or do you have no idea what the output of any given zone should be?

  • hot_rod
    hot_rod Member Posts: 23,278

    You can rent ultrasonic flowmeters online. That is the quickest, least invasive way to get accurate readings

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jumper
    jumper Member Posts: 2,385

    All zones open gives max flow. Only most distant open, minimum flow.