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High Efficiency for DHW production

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Uni R_2
Uni R_2 Member Posts: 589
If the boiler can run a high enough ΔT, perhaps try to heat the water in 2 steps?

The final heat exchanger would get the hot boiler supply water first and then its return (which would be above condensing temps) would be be the supply for the secondary heat exchanger which does the first stage of DHW production (preheat the DWH to a certain level).

With a boiler that can handle a ΔT of 30 to 40° you could possibly use a 160° supply along with a final 120 - 130° return, while making 140° DHW in the second stage.

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  • JBW_2
    JBW_2 Member Posts: 67
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    high efficiency for DHW production

    Hello all,

    Has anyone used a high eff boiler solely for DHW production through a heat exchanger?? Will I ever condense??

    Regards,

    Josh W
  • Glen
    Glen Member Posts: 855
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    yes to both -

    > Hello all,

    >

    > Has anyone used a high eff boiler

    > solely for DHW production through a heat

    > exchanger?? Will I ever

    > condense??

    >

    > Regards,

    >

    > Josh W



    It depends on your expected DHW temps. Very hi temp DHW (and then mixed down) offers some challenges but normal DHW production temps (115 - 120) will condense.
  • Glen
    Glen Member Posts: 855
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    yes to both -

    It depends on your expected DHW temps. Very hi temp DHW (and then mixed down) offers some challenges but normal DHW production temps (115 - 120) will condense.
  • Guy Woollard
    Guy Woollard Member Posts: 82
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    Sure

    I have seen it done, especially where the water quality is sketchy.

    You would want to use a good indirect, capable of giving you a high Delta T.

    Supply that with 160 degree water; that would put your return water at 130 to 135 ish, making the boiler condense.

    Remember, in doing this, you will be "firing" the indirect below it's recommended rate, so you may have to compensate by going up a size in volume ( without going too much over the rating of the boiler)
  • Constantin
    Constantin Member Posts: 3,796
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    or...

    use a high quality tank like trangle-tube's series, etc. to provide you with a very large HX surface that requires a very low supply temperature, maximizing your chances to have the boiler condensing all the time.
  • hot_rod
    hot_rod Member Posts: 22,158
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    a dual coil indirect tank

    is my current method. I use the Heat-Flo tanks with two 1-1/8" coils. Lots of coil or surface area and lowest possible return temperatures to the boiler will be the ticket.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
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