An Open Storage question

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by nhjohn, May 4, 2008.

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  1. nhjohn

    nhjohn
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    After an extensive amount of research, I'm still not quite getting the open storage concept. Why is a heat exchanger necessary between the gasifier and open storage? Why can't I put a line at the bottom of my tank, add a circulator, and run it through the gasifier and back into the top of the tank (assuming the gasifier is pressurized)?

    Also, if I use a flat plate HX, aren't I running a line from the bottom of the tank, through the HX, and back into the top of the tank? What does the HX add (besides maybe freeze protection if I use glycol)?

    In terms of extracting heat from the tank, can I siphon water off the top of the tank, run it though a injection pump to create optimal temperature, and then through the supply zones? Or would I need to have a HX between the tank and supply lines as well? If so, why?

    Any and all responses are greatly appreciated.
     

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  2. free75degrees

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    The boiler water is pressurized, which means that if you had it connected to an open tank of water the water level would keep rising since there would be nothing to resists the pressure. The tank would overflow. It would be like having an open faucet, albeit at lower pressure than your domestic water since there is a pressure drop valve between your domestic and your boiler water.
     
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  3. nhjohn

    nhjohn
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    What I don't understand is: if you circulate water from the open tank to the boiler, it pushes water out the boiler and back into the tank. How would it overflow? I'm so confused?
     
  4. jebatty

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  5. hkobus

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    I think the confusion starts with mixing open and closed systems. Closed systems are just that, closed. They have pressure build by expansion of the fluid, and as said above are often connected to the domestic supply with an automatic refill valve that responds to a drop in pressure.
    An open system is open at some point of the system, and therefore will not build anymore than atmospheric pressure. The expansion of the fluid will go to the area open to the atmosphere. If this is a tank, heat-storage or vented expansion tank, it should be sized to allow for this expansion.
    Combining these two systems can be done through a HX (plate or coil) where the closed system remains closed and under pressure and the open system as it was.
    Depending on what boiler you choose, you may be able to run either system.
    I am thinking of going open next fall, with storage (open, no pressure) but vapor sealed in the basement and the boiler in the boiler shed outside 1 floor higher. As long as there is no opening at the higher points in the system(allowing air or water from other sources to enter) there will be no change in the water level in the basement storage, other than from expansion.
    This probably did not help much, but the best way I can explain the issue.
    Many older systems are open and gravity flow, with hot water rising and cold falling back to the boiler.

    Henk.
     
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  6. deerefanatic

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    That's what I'm doing. Open system with vapor barrier (wax) to minimize oxygen ingestion and evaporation.
     
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