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  • question on thermo siphoning

    a friend of mine and I are considering making a solar/wood stove domestic water heating system,

    Background

    since one can not easily control the rate of the heat, at some time one may have to dump the heat out of the tank to keep it from boiling,

    FIRST this is a non pressurized system, or an OPEN system, not a closed system,

    yes T&P valves will be used in the tank and on the solar panel/ wood stove loop, and any location that may have a shut off on it so there is no way of creating dangerous pressures in the system,

    now with that said,

    I am concerned about over heating the water in the storage tank,

    a tempering valve will be put on the out going to the domestic hot water use, (this will be provided by suction pump on demand only),

    QUESTION

    I see many systems on the net, use a heat dump system, some dump water to the drain, (fine if one has a surplus of water, in this case, the water is very limited, in this situation),

    others pump through a heating coil (such as radiant floor heat) good but not applicable in this situation,

    this is my IDEA, I made a small manifold via a short section of 2" pipe, and made flanges on and put on the out going water, with a automotive 160 degree radiator thermostat in it, and the plan is to go into a water to air heat exchanger,
    (not positive what type of exchanger but may just be some water base board heaters or the guts of them),
    now I would like to eliminate pumps and stitches and the need for electrical power, of any type on this set up,

    so I would like to set the exchanger up so when the thermostat opens it will thermo siphon, the hot water enter into the exchanger and cool and then enter the bottom of the storage tank,

    the actual question I have is where does the exchanger need to be placed, to get the best siphon action, and not lock up,

    A, above the manifold,

    B, level with the manifold,

    C, or below the manifold,

    to properly siphon to cool the water in the storage tank?

    the heat exchanger would be most likely with in 12 to 16 inches of the storage tank. or (start with in 12" to 16" If the base board heat tube was used)
    if a radiator type exchanger was used with in 12 to 16 inches as well,

    (the way the gravity feed is I can only go about 4" above the storage tank max. as when the supply tank is low the bottom is only about 4" above the heaters storage tank.)

    there will be a T&P valve that will just dump water if it gets to 210 degrees, and it is vented to atmosphere,

    my preference is level or below for space requirements, and some concerned that if above it could air lock, (yes I know there are automatic air dump valves, but the less things to go wrong I think the better),

    The first picture is just placement of the heat exchanger, for better visualization

    the second picture will be how the wood stove coil will work,

    and the third is the combination of the wood and solar, but NOTE: the picture does not show all the T&P valves and proper connections into the storage tank, the wood stove will basically be sued for winter and solar for summer use, (it is just an example of the combination of the two on the same system, (actually the solar will most likely be a drain back system using a pump),
    Attached Files
    Last edited by BHD; 12-13-2010, 02:24 PM.
    Push sticks/blocks Save Fingers
    ~~~~~~~~~~~~~~~~~~~
    "The true measure of a man is how he treats someone who can do him absolutely no good."
    attributed to Samuel Johnson
    ~~~~~~~~~~~~~~~~~~~
    PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

  • #2
    Re: question on thermo siphoning

    make yourself a miniature natural draft cooling tower.

    get some old car or truck radiators and lay them flat so the air has to rise up through the fins.

    place the radiators in a vertical duct or chimney or maybe use a piece or large diameter corrugated pipe (36" maybe) of the right diameter with the radiator at whatever height you determine you need in relation to the rest of the system.

    ensure that the tower base below the coil is open to allow air to enter the tower. measuring the height of the tower from the top of the openings at the base, the coil should be about 1/3 of the way to the top from there. the temperature differential will create a draft and draw air in around the bottom. this air will sink the excess heat from your solar heat source and send it up into the atmosphere. air inlet sq footage should be equal to the opening at the top of the tower.

    no moving parts to maintain, no pumps, electric, etc.

    lay out multiple radiators on the same level and use a larger dia pipe or add additional pipes to create more towers as needed to scale to your needs.
    ---------------
    Light is faster than sound. That's why some people seem really bright until you hear them speak.
    ---------------
    “If I had my life to live over again, I'd be a plumber.” - Albert Einstein
    ---------
    "Its a table saw.... Do you know where your fingers are?"
    ---------
    sigpic http://www.helmetstohardhats.com/

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    • #3
      Re: question on thermo siphoning

      forgot, the higher the tower the greater the temperature differential between the inlet at the base (ground level) and the outlet or top of the stack. The greater the temp difference the better draft just like any chimney.

      Do you have an old silo no longer used on site? you could convert it into a nice cooling tower. 40 or so feet of height would work great.

      http://www.cheresources.com/ctowerszz.shtml

      Some design info on mechanical draft towers at the link above, but i am talking natural draft so no moving parts so no spray ring or fans or pumps. a natural draft tower would not be as efficient but all its work is free and should be able to scale it to handle whatever heat you need to shed from your solar array.
      Last edited by Bob D.; 12-14-2010, 09:37 AM.
      ---------------
      Light is faster than sound. That's why some people seem really bright until you hear them speak.
      ---------------
      “If I had my life to live over again, I'd be a plumber.” - Albert Einstein
      ---------
      "Its a table saw.... Do you know where your fingers are?"
      ---------
      sigpic http://www.helmetstohardhats.com/

      Comment


      • #4
        Re: question on thermo siphoning

        Thank you for the Idea on the mini cooling tower Idea, was thinking of some way to help move air across the coil but that had not crossed my mine,
        Push sticks/blocks Save Fingers
        ~~~~~~~~~~~~~~~~~~~
        "The true measure of a man is how he treats someone who can do him absolutely no good."
        attributed to Samuel Johnson
        ~~~~~~~~~~~~~~~~~~~
        PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

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