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Biogas 60 pool heater

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by MarkW, Jun 15, 2013.

  1. MarkW

    MarkW Member

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    So, I'm using my new gasser with my 12,000gal pool as a load to learn to operate my boiler. I was a wood furnace user previously. I've got what is rated as a 155K btu HE connected between the two. My question is this: as the temp in the pool has risen, the frequency of the circ pump off times has decreased and the boiler temp is catching up to the set temp more frequently.
    I suspect this is because the ability of the heated boiler fluid to transfer btu's to the pool water is decreased as the pool temp rises. Am I right?
    How does this affect storage charging when winter rolls around? I'm thinking of targeting a storage temp of 180. Will I have to set my boiler target temp higher to get there?
    Thanks,
    Mark

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  2. mustash29

    mustash29 Feeling the Heat

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    Differential temp (delta T) is what drives the heat "flow" or rate of heat transfer. As the temps get closer together the net heat transfer is slower.

    If you increase pump speed you should be able to then transfer a bit more BTU's.

    In theory, twice the delta T will move the same amount of heat as twice the flow.
  3. MarkW

    MarkW Member

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    So, I'm running a Taco VDT circ pump with a delta of 10. Would I be better at increasing the delta?
  4. mustash29

    mustash29 Feeling the Heat

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    I'm new around here so I really can't help you with boiler & componet specifics.

    My background is 10 yrs navy nuclear power & allmost 14 yrs in the trash to energy incineration field. Trust me, I know all about burning wet stuff!
  5. MarkW

    MarkW Member

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    If I could get my hands on a Navy reactor for residential heat/electricity, I don't think I'd bother with wood! ;)
    flyingcow and BoilerMan like this.
  6. BoilerMan

    BoilerMan Minister of Fire

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    Mark can you post a diagram of how you have the boiler and HX and pool connected and where the Taco VDT is located in that circuit. Then we can beter help answer your questions.

    BTW congrats on the new boiler!

    TS
  7. MarkW

    MarkW Member

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    TS
    I've got the pump on the boiler inlet loop w/exhcanger ahead of that. The exchanger is in the filter pump loop. I know this isn't ideal considering the gpm of the pool pump. I'm just playing with this at the moment to learn the boiler operation finepoints.
    Eventually, I'm going to have 1500g storage in place of the pool and exchanger. I guess rereading my OP it was a bit poorly worded.
    What I'm interested in knowing is how the transfer efficiencies change as the boiler/storage temp and exchanger/load temp narrow?
  8. stee6043

    stee6043 Minister of Fire

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    It's a bit difficult to make broad generalizations with respect to heat transfer. Our ability to transfer heat from one place to another is equally as impacted by heat exchanger design (or transfer medium) as it is input temp, output temp and flow. In theory, you should be matching the design parameters of your heat exchanger in order to maximize heat transfer. Doubling flow will have wildly different net effects depending on the HX.
  9. stee6043

    stee6043 Minister of Fire

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    Most of us storage users will set our ouput temps as high as possible. If your boiler will go to 195 there is no reason to limit it at 180 (assuming your system is capable of safely handling 195 degree water).

    There are not many of us who are able to acheive storage temps that match the boiler output temp in the real world. With 195 output on my boiler I think my typical max on storage is 185 +/- after a typical burn...
  10. MarkW

    MarkW Member

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    I guess that's what I was looking to know, stee6403.
    When set up, my storage will be capable of 190+ so I guess my boiler won't over-run under normal operating circumstances.
  11. goosegunner

    goosegunner Minister of Fire

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    I am confused by your problem or perception of what is going on but I can tell you that my boiler heats my pool much better with the storage. I have a 360,000 btu exchanger and I can get a 40-50 degree delta t as long as I want when heating the pool. It does not matter much if the pool is 65 or 85. The storage acts as a secondary buffer. It will still climb in temp slowly as I heat the pool.

    I heated the pool for a year before I added storage. The problem I encountered then was if the boiler wasn't good and hot the pool exchanger would pull down the boiler temp and the pump would stop. If I had a good coal bed and a full load the boiler would climb and hit the set point and go into low fan.

    The storage smoothed everything out. I used it this afternoon to have some people over. Went from 80 to 87 for a nice swim temp.

    gg


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