Getting the best out of my plate HX

warno Posted By warno, Nov 9, 2017 at 10:45 AM

  1. warno

    warno
    Minister of Fire 2.
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    Jan 3, 2015
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    illinois
    I'm wondering if i can get more out of my plate HX i use to charge my storage. My system consists of a 20 plate HX with a grundfos 15-58 on the storage side running on low speed and another 15-58 on the boiler side running on medium speed. I run batch burns in my boiler and while firing my boiler stays about 10-20 degrees ahead of my storage until the fire starts dying down then they balance out at alittle lower then I'd like (about 165-170).

    Is there a better way to run my system to keep the storage alittle closer to the boiler while it's in the peak of the burn? Would delta T pumps help with this?
     
  2. maple1

    maple1
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    You might be able to tune it in a bit by monitoring the ins & outs of the HX to see what the dTs are on each side, and maybe adjusting circ speeds. But a given sized HX can only transfer so much heat. Example, if you could slow the flow on the storage side you would be a bigger spread & higher exit temps but it would take longer for all the storage to circulate through. So net gain would be not much - total BTU transfer would be the same over a given time. I might have gone bigger on the HX - I have a 20 plate on my DHW and it does good at that but I think it would be slow heating up my storage. I forget how close the DHW out temp gets to boiler supply temp - I will have to watch it closer next time it is running. I have digital temp guages permanently tied to the ins & outs.

    That likely didn't help much...
     
  3. warno

    warno
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    Jan 3, 2015
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    I thought about going with a bigger HX but i was concerned about drawing too much from the boiler. I'll try to do alittle bit of watching the ins and outs on my temps periodically through a burn maybe this weekend.
     
  4. Bob Rohr

    Bob Rohr
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    Generally speaking the higher the flow rate the more energy you transfer. Staying below excessive velocity in the connected piping of course.
    3/4 pipe can handle 7 gpm comfortably, 1" around 12 gpm.

    If it is a 5X12 20 plate I suspect even speed 3 will not over pump it, depending on pipe size that you used.

    The free online simulator at flat plate website allows you to enter all the various numbers and get output, flow rate, pressure drop etc. It's sometimes easier to click buttons and get various options and answers.
     
  5. warno

    warno
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    Jan 3, 2015
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    I used the flat plate website to source my HX but without knowing the actual output of my boiler being homemade. So i was kind of guessing on some of the numbers.

    My HX is a 5 x 12 and it's fed on both sides with 1" piping. Are you suggesting i turn up my speed on both pumps or just one or the other?
     
  6. Bob Rohr

    Bob Rohr
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    Jan 9, 2008
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    Generally speaking the higher the flow rate the more energy you transfer. Staying below excessive velocity in the connected piping of course.
    3/4 pipe can handle 7 gpm comfortably, 1" around 12 gpm.

    If it is a 5X12 20 plate I suspect even speed 3 will not over pump it, depending on pipe size that you used.

    The free online simulator at flat plate website allows you to enter all the various numbers and get output, flow rate, pressure drop etc. It's sometimes easier to click buttons and get various options and answers.

    Turn them both up. If you hear a lot of rushing water you probably have flow at or over 5 feet per second. That is about the speed that you start to hear flow in piping and really don't want to exceed that. Ideally 4 FPS is a target max. flow.

    Certainly no harm in oversizing a HX other than cost. The more surface area the better the exchange.

    Close approach is a heat exchanger term used to describe a condition where A and B side are within a few degrees, when you design a close approach you will notice the size of the HX increases.

    But without some hard data it's tough to get an exact size or predict performance. Invest in a BTU meter and see exactly what kind of work your boiler is doing :)

    On the district energy systems in Europe you purchase and pay for your energy via BTU meters, very accurate devices.
     
  7. PassionForFire&Water

    PassionForFire&Water
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    Bob, any possible recommendations for BTU meters here in the US?
     
  8. Bob Rohr

    Bob Rohr
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    I saw this company at a trade show, they had some simple and affordable meters.

    Basically you measure flow in GPM and the temperature difference between supply and return, that gives you the actual energy amount being transfered.

    http://www.onicon.com
     
  9. vtwoodheater

    vtwoodheater
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    Nov 1, 2015
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    What is your plate exchanger rated for BTU wise? When I was running my outdoor wood boiler, I had a 40 plate exchanger. Don't recall the physical dimensions, but it was rated for 400,000 BTU's +/-. I sized it according to the maximum output of my boiler. Never had a problem with that aspect of the system.

    A quick search found a 350,000 BTU exchanger for $185.

    Cheap, throw it in, never worry about your heat transfer rate again. My 2 cents.
     

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