Over heating issues...

warno Posted By warno, Jun 5, 2018 at 6:59 PM

  1. warno

    warno
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    I had a thread during the winter on my issues with caviation and over heating.

    https://hearth.com/talk/threads/cavitation-issues.166597/

    I've finally started tearing into my system to see if I can find the flow issue on my boiler side. I was seeing huge delta Ts on the boiler side of the FPHX. First thought was my pump was damaged from cavitating. The impeller looks good. So next thought was my FPHX scaled up. I pulled it out of the plumbing today and from looking in the ports i couldn't see anything. Looks like the day I installed it. My only other restriction could possibly be the themomix valve being stuck semi closed and allowing bypass of boiler flow. I didn't get a chance to pull the valve ti look at it but other then that what could be my loss of flow?

    I went from delta Ts of 10-15°F at the beginning of the season to 40-45°F towards the end.
     
  2. maple1

    maple1
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    Ah yes, that was an epic thread.

    Are those dTs across the HX or across the boiler?

    Was there any change in dTs on the system side?

    I don't have experience from inspecting a cavitation damaged circ, but wonder if there could be an issue without it being obvious to the eye? I think I remember about there being a lot of noises then. Maybe something in the wear surfaces where the impeller shaft spins that would increase resistance to spinning?
     
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  3. Chris Hoskin

    Chris Hoskin
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    higher delta T means you are moving MORE water, not less.
     
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  4. brenndatomu

    brenndatomu
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    Unless the cavitation was very mild and did not happen much, there would be very visible damage. Do a little reading up on cavitation, is is quite destructive to a pump.
    I was in a class a couple years back that had a pump with a clear case, you could see what was happening when they throttled various valve to make it cavitate...it can actually be quite violent
    pump-cavitation-10-638.jpg
     
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  5. maple1

    maple1
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    If you move more water thru the boiler & that side of the HX, wouldn't that narrow the dT on that side?
     
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  6. E Yoder

    E Yoder
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    I think I would agree with maple1, but maybe we're not all talking about the same thing.
     
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  7. Chris Hoskin

    Chris Hoskin
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    Correct! (sorry, brain fart) More flow means narrower delta T across the heat exchanger (transfering more energy).
     
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  8. Chris Hoskin

    Chris Hoskin
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    yep, sorry, I got that backwards
     
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  9. E Yoder

    E Yoder
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    Lol, I have more of those the older I get..
     
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  10. warno

    warno
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    @maple1 The delta Ts were higher on the boiler side of the HX vs the storage side. When they used to ride also identical.

    And the delta Ts didn't change any in the system.

    The circ I'm running has a plastic impeller. It's probably composite of some kind but either way it showed no signs of wear. And it had caviation going on for about 2 seasons on and off. When the boiler would reach anything mid 170s it would be very faint but closer to 180 and over it sounds like the circ was eating gravel.
     
  11. BoiledOver

    BoiledOver
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    @warno Do you have good news to report concerning your system modifications?
     
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  12. warno

    warno
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    I've completely changed things up. I'm going to start a thread here in the next few weeks about my changes. I've eliminated probably half or more of my head loss on both sides of the FPHX and I've also step up my FPHX size by more than 10 fold.
     
  13. BoiledOver

    BoiledOver
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    Sure are hoping for dramatic improvements, seems like that beautiful boiler should easily handle your needs.
     
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