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Wood Boiler

Kevin_28 Member Posts: 4
Hi everyone. I was looking into the New Horizon Corp. wood gasification boilers. My question to everyone is what is the best way to hook these units up? The unit only holds 20 gal. so I really think it should be hooked into a buffer tank/indirect so there is at least some more heat storage compacity. If a reverse indirect is used, (Wood Boiler water goes through the coil and heating system water goes in tank) and you set the aquastat on the tank to maintain say, 180F water, what happenes when the aquastat shuts the pump off and the boiler is still burning wood? Shouldn't there always be water circulating through the wood boiler while it is burning wood? Any thoughts or suggestions would be welcomed. Hotrod, I know you do some work with wood boilers, how do you hook yours up? The unit I would need is a 25KW or about 85,000 BTU one. The home where this unit will be installed is a 1200 sq. ft. ranch with full finished basement + heated garage making the total square footage about 2600 sq. ft. Heat loss calc for baseboard and pannel rads. came out to about 70,000 BTU/H heat loss plus I need to allow for DHW.


  • Steve Ebels_3
    Steve Ebels_3 Member Posts: 1,291
    Combustion wise.............

    The most efficient way is to burn ALL the wood, leaving no smoldering, creosoting low temp fire and store all the btu's.

    So. How many btu's in a load of wood for your particular boiler? Find that out and do the math working with a 20-30* temp differential and you'll know how many gallons of storage capacity you'll need. If your firebox will hold the wood equivalent of 200,000 btu's you would need to fill it 3 times to get eight hours worth of heat in the example below.

    You can also work backwards begining with the heatloss of the house and size the boiler accordingly. In other words, if you have a heat load of 85,000 btu's and you want to fill the stove 3 times on a design day you need to store 680,000 btu's per fill. One gallon of water giving up 20 degrees per hour = 10,000 btu's. This would mean a storage capacity of 68 gallons, recharged every 8 hours. This of course depends on your heat emiters being able to deliver the required heat at the temps you'll be working with.

    There are so many variables when working with wood that it's best to err on the over capacity end of things in my experience.
  • hr
    hr Member Posts: 6,106
    As you know

    it is hard, almost impossible to match the burn to the load. This is one reason the Euros like to see large buffer tanks. Burn the stove as hot an as efficient as possible, regardless of the load, and let the excess spill into the buffer.

    Also the buffer can serve as a dump load should the boiler over run the load and tank.

    a simple protection method is to have an additional aquastat, or setpoint control that would again start that buffer tank pump to dump excess heat into the tank.

    Siggy has some excellent piping drawings for a primary secondary using a variable speed circ on the boiler to offer return protection, which keeps the boiler operating at over 140 temperatures to avoid condensation and inefficient burns.

    His drawing also has the buffer only on line when needed, so a back up gas fired boiler would never "see" the buffer capacity.

    I know he worked with tekmar for a nice VS and diffefential control package to get all this to happen at the correct time. It gets fairly complicated, piping wise, but is plenty doable.

    You notice how the Euros handle all this with the crazy three way thermostatic/ pump block. That is another (less smart) way to protect the boiler and dump excess. Three way thermostatics in that capacity really burn some serious pump head. The are mostly 220 V 50 cycle, however. although it sure looks like a Wilo head to me :)I like the small off the shelf circs with a VS control, or a Miximiser with it built in.

    I'll check with Siggy about sharing his drawings, or you could attend his class in Bozeman, Montana on the 15 of July. I'll be there :) He covers wood and solar nicely in the course booklet. His favorite method is to get a 500 or 1000 gallon lp tank (new) and use it as a pressurized buffer. I have tried a bunch of different open tanks. Concrete, HDPE pallet tanks, barrels, you name it. Closed, pressurized, well insulated make a lot more sense, but add cost.

    hot rod

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  • Kevin_28
    Kevin_28 Member Posts: 4

    you could say set the built-in tank aquastat at 160 (turn on pump at 150 and off at 170)and then have an aquastat on the boiler turn the pump on regardless of if the tank needs heat or not at say, 185? Also, what about Tekmar controls? Do you think we could use these wonderful (I LOVE TEKMAR) controls on wood systems?
  • Kevin_28
    Kevin_28 Member Posts: 4

    with an 80 gal. buffer tank, the boiler shouldn't have to be filled more than two to three times a day? I don't think that is bad.
  • hr
    hr Member Posts: 6,106
    With a copy of Siggys HDS

    you could play out a bunch of buffer tank "what ifs" You need load info, buffer size, delta T insulation value, etc Then you could get some exact answers.

    I'll bet hydronicMike at tekmar would be happy to share control drawings and options for wood. He has helped me with a few nice options as well as Siggys complex wood/ solar/ buffer/ oild fired/ multi temp systems.

    I have used the 150, 155, and some guys use the multi mix 369 for solar and wood applications. Proably dozens of control options. the correct one would be built around your specfic needs. It's fun to play with control options, it really makes you think. Piping is simple for me it's the communication of all the pumps and temperaturer controls that I struggle with. Luckily we have the help of control gurus here :)

    hot rod

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