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Two pumps, one tank

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Rich L.
Rich L. Member Posts: 414
How do you plan on controlling your system? I have a GSHP as my only heat source and in long stretches of cold weather (20 below) it struggles to maintain comfortable temps throughout the house. I've considered adding a small wall hung mod-con boiler to help in the coldest weather but I'm not sure how to best control it. No matter what strategy I come at it with it seems the boiler will take over once it kicks in, wether setup as a second stage or off of an outdoor temp setting. I really want the heat pump to remain the primary heat source. Has anyone tried this before and how did you do it?

Thanks for the help, Rich L

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  • Blackoakbob
    Blackoakbob Member Posts: 252
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    two pumps, one tank

    Ladies and Gentlemen,
    I am in the beginning of a piping layout for a gshp and a modcon boiler both feeding a buffer tank. One as a primary and one as a backup.I'm wondering, from your experience, will the in-pump check valves be adequate to prevent flow thru either of the heat sources? Should I use a flow controller like the old B&G? What about inducing a flow thru my secondary loops going out of the buffer tank when either primary pump runs? Sorry, I'm not capable of adding drawings at this time. Thanks for your recommendations. Best Regards,
    blackoakbob
  • ALH_4
    ALH_4 Member Posts: 1,790
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    Decoupled

    From your description, it sounds to me like you are truly hydraulically decoupled at the buffer tank. I am a little hesitant to rely on the internal check valves in critical applications where failure could go unnoticed and could adversely affect the system's operation. I would install separate check valves in that case. If there is any debris in the system, it tends to get hung up on those small internal check valves.
  • Blackoakbob
    Blackoakbob Member Posts: 252
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    weighted type flow control

    Thanks for the reply Andrew. I had thought that the weighted flow valve may have an advantage over a simple swing or spring check. It may just add pressure drop.
    Best Regards
  • hot_rod
    hot_rod Member Posts: 22,141
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    depends on the buffer tank also

    if you have, or can find one with at least 4 separate connections that helps a lot. If you have all 3 circs pulling and returning from the same connection point, the de-coupler effect goes away.

    Ideally connections across the tank from one another would provide for excellent "de coulping"

    With electric water heater tanks I use the top hot and cold connected (with the dip tube removed;) I use a 1X 3/4 x 3/4" tee to get two 3/4 connections up to 1" quickly.

    Then I use the two element holes for the radiant S&R. This spreads the "tank" out a bit. Connect the boiler at the same connections as the geo. i'd use checks on the circs, as well as the return side of both geo and boiler.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 22,141
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    a quick drawing for you

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Blackoakbob
    Blackoakbob Member Posts: 252
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    picture worth a...

    Thanks for the drawing, I would not have thougth of putting the heat into the top and circ out of the bottom. I was planning on feeding the heat input to the middle of the tank fittings and supply the emitters from the top and circ into the bottom. I will take your advice and put checks at the pump and at the supply. Best Regards,
  • Ted_5
    Ted_5 Member Posts: 272
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    HBX Controls has

    a Geo control called ECO-1000. It will give you out door reset and when the geo can't keep up, it will kick on the back up. Once the back up gets to set point the the geo takes over again.

    Ted
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