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Injection loop piping- Does it Matter

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Eric
Eric Member Posts: 95
in THE MAIN WALL
Does it matter if the close coupled connection for the injection loop is on the suction or discharge of the radiant loop ciculation pumps?

I guess you need to place sensor so mixing can occur.

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  • eleft_4
    eleft_4 Member Posts: 509
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    Piping

    On the suction side. The amount of water returned from the radiant panel to the primary loop is equal to the the amount of water injected into the radiant loop. It starts mixing ahead of the radiant circulator. The injection pump control sensor is placed after the circulator where the water should be mixed.

    al
  • hr
    hr Member Posts: 6,106
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    More injection thoughts

    from Radiant Basics. In direct injection the the return injection riser sees the radiant return temperature.
    In reverse injection the return riser sees the radiant supply temperature, decreasing the delta T between the in and out injection risers. Which in turn requires less throttleing back on the flow restrictor valve. The check valve placement is important so the distribution pressure will backseat the swing check to prevent thermal migration when the injection pump shuts down.

    I have always used direct and the smallest pump I can get. A 15-10 Grundfos, or equivalent, is usually plenty of oomph for most residential stuff I do. The pumps with intergral checks are handy also for direct injection.

    Yet another spin is to install the injection pump on the return riser with the flow setter valve downstream of the pump. The Delta P of the pump will be used up across the throttle valve, so the delta P across the other injection riser is small, according to Siggys thoughts on this arrangement.

    The old B&G manuals showed the pump on the return riser, probabaly for the same reason boilers were shipped with pumps on the return side. They see a lower temperature for longer life. That was important for "early version" pump seal material... Before my time of course :) Cooler temperatures translate into longer pump life. Probably not as critical on modern wet rotor pumps, but hey, why not :)

    hot rod

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