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Wood Boiler - Heat Storage

Chuck_7Chuck_7 Posts: 71Member
A friend is connecting a wood boiler to his existing heating system (gas boiler, baseboard, 1 pump, 4 zone valves).
I am interested in any approches to heat storage (to store excess heat when the boiler is hand stoked).
If this topic has been addressed before please direct me to the thread.

Comments

  • hrhr Posts: 6,106Member
    A favorite topic of mine

    Generally you want 250- 500 gallons of storage. Of course it needs to be well insulated.

    Insulated tanks in this size range get pretty expensive, especially in a pressurize-able tank.

    I have used old propane tanks, usually found for about a buck a gallon. They are built to handle the pressure of a typical hydronic system 15- 30 psi, and them some :)

    I have also done some unpressurize-able insulated tanks, much easier and cheaper to come by. This works best with a heat exchanger inside or wrapped around the outside. This becomes your pressurized loop through the boiler.

    there are some tanks built for this application. tarm boilers offer a 500 gallon open type buffer tank, with a copper tube HX built inside.

    You will need to address bacteria growth in an open unsealed tank, however. Those little buggers thrive at hydronic temperatures! that was the eventual downfall of my shop buffer tank.

    I used the bottom half of a concrete septic tank in my shop for a buffer tank. I bought some EPDM roofing material to line it and make it waterproofed. I used 1-1/4" copper K coils as the HX. A loose fitting 2" foam cover kept the heat in. Barely!

    John Siegenthaler has an excellent buffer tank sizing module on his HDS software. This will help you size and run different cycle times based on loads. www.hydronicpros.com for a demo.

    hot rod

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  • Chuck_7Chuck_7 Posts: 71Member
    Secondary vs. Primary

    Thanks for the input.
    My friend did not want to pay the cost of the Tarm "hot tub". Some of his alternative ideas are ify.
    I think having the buffer fluid part of the main loop would be better (no HX/secondary fluid) except of course for the cost of the storage.
    Your idea sounds pretty good. Do you have a problem with humindty in the room with the tank (the secondary water temperature would have to get pretty high)?
    Also I do not think a rigid tank is going to get into his basement (though maybe the garage).
    Maybe there is some other secondary fluid or material that could be used.
  • Dan PeelDan Peel Posts: 431Member
    Control

    I have a little different take on buffering wood fired boilers. Like any other boiler system you need to take control over the fuel and/or air. Most OWF units are built with enough storage to effectively absorb the heat they produce during low fire, closed draft times and all of them require constant flow through the underground piping. Storing the BTUs in the fuel has far lower standby losses than trying to maintain copious amounts of remote fluid hot. If you have a three stick day use three sticks, you don't need to fill them each time you visit. Enjoy......Dan

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  • hrhr Posts: 6,106Member
    Burn em hot if you've got em

    I agree with Dan in the case of the large volume outdoor units, where buffer is built in.

    Still a hot efficient fire is prefered for fuel efficiency and less emissions. As such, a hot fire with some buffer, or overheat absorption space is nice as lots of folks stoke (the fire) big in the morning and hope to have heat when they get home from work.

    If you can attend the fire all day, yes, by far the best burn is a hot burn closely matched to the heating load.

    Still I would rather see a long hot burn with some thermal storage than a fire that bounces up and down all day against the air control. Ssmoldering and smoking like crazy when the damper, or blower kicks it out of the smolder stage.

    Or worse the fire goes out and you start from scratch when you get home to a cold house :)

    Getting used to wood burning takes some time and practice with an eye, always, on incoming weather. If it were easy everyone would have wood heat, again :)

    hot rod

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  • WeezboWeezbo Posts: 6,232Member
    or coal:)

    big chink of coal helps wood burners get away from fricking with the thing :) coal sorta lasts longer:)
  • Mike T., Swampeast MOMike T., Swampeast MO Posts: 6,928Member
    Hmmm...

    "Getting used to wood burning takes some time and practice with an eye, always, on incoming weather. If it were easy everyone would have wood heat, again :)"

    Human outdoor reset.

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