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Thermostatic Mixing Valve rec?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by kuribo, Feb 21, 2013.

  1. kuribo

    kuribo Feeling the Heat

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    I was planning to use a modulating three way valve to mix supply and return between the tank and the circulator to drop the temp to 120F. Piping from the tank to the valve would be copper. The valve is rated to 248F so I don't think the 190F would be a problem (?).....Would I still want to return to the top of the tank?

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  2. JP11

    JP11 Minister of Fire

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    My tanks will get to 195 top to bottom when the boiler is running. It of course mixes down to 110 for the in slab radiant and 145 to 150 for the staple up.

    When the in slab is running.. the return to storage water runs only about a 10 degree delta T. So my injection loop is running 195 out, 185 back. That's all the hot water the loop will take. I've set my injection loop feed pump on it's slowest setting. Even when all the zones are calling in the house (save DHW) I don't see more than a 30 degree drop.

    Everyone's setup is different. The plumbers looked at me like I was nuts when I kept telling them to put in Ts and thermometer probes. But I can SEE where my heat is going now.

    JP
  3. kuribo

    kuribo Feeling the Heat

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    Where do you have the boiler and distribution plumbing located on your storage tanks? Boiler supply on top, return on bottom; distribution supply off the top, return to the bottom?
  4. Floydian

    Floydian Feeling the Heat

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    Hi Chris,

    Your plan sounds similar to my system. Check out the link in my sig.

    My boiler only feeds storage-supply to top, return from bottom with a very defined thermocline while charging storage.
    Infloor heat supply draws off the top of storage and returns to the bottom through a dip tube. Again, no mixing while discharging storage.
    Maintaining stratification while discharging storage will be more important for me when I add DHW to the equation.

    Constant circulation with outdoor reset is simply awesome! I find I am very happy with a 20::F ::DTT on my low temp radiant floors, allowing half the gpm's vs a 10::F::DTT. Maybe this would work for you or maybe not but a variable speed ECM pump would allow you to pretty much dial in whatever temperature drop you want. I have my Alpha set on fixed speed 1, drawing 6 watts and pumping 1 to 2 gpm depending on what kind of flow the TRV's are allowing. Of course my heat load is less than half of yours but less electricity is always better and constant circulation doesn't necessarily mean more electrical consumption vs on/off control.

    Can't really offer anything on the mixing valve recommendation besides outdoor reset.

    Not sure this helps much....BTW nice work on the house! Love the aesthetic value (just not the thermal bridging).

    Noah
  5. kuribo

    kuribo Feeling the Heat

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    Are you able to get your tank a uniform 180-190F?

    I am planning on using a variable speed circulator...I am wondering if I will need balancing valves in each of my 4 zones to get the correct flows???

    Your system looks great! Thanks for pointing me to it.

    Yes, the downside to my Japanese home is the thermal bridging. That is why the post and beams are 10" thick. What can I say, I am a fool for aesthetics....

    Thanks again for sharing.
  6. Floydian

    Floydian Feeling the Heat

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    Honestly, I haven't gone above about 170F. Party because I only need to fire every other day at avg winter temps and because I need to get more insulation around my tank.
    I have no doubt 190F top to bottom is within my boilers capabilities.

    It would be nice to have the ability to send more flow to the areas of greater heat loss.

    A fool? No way! It's your house, it should be exactly what you want. But your nice heating system is going to deny you that authentic Japanese farmhouse feel (temperature wise).;)

    Thanks for the compliment and keep us posted on things (pics),

    Noah
  7. JP11

    JP11 Minister of Fire

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    Really simple. Supply from top 1.25 inch.
    Return to bottom 1.25 inch.

    I have an injection loop setup to the hot leg of my oil boiler.

    Other supply and return to/from wood boiler that's 1.5 inch plumbing.

    JP
  8. kuribo

    kuribo Feeling the Heat

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    Just an update:

    I choose the Tekmar 712 and 741, which is a 1-1/4" three way valve and modulating driver. Total cost was a bit over $350.

    The 712 valve was $112, the next larger size, a 1-1/2" valve, shockingly, was about three times the cost!
  9. ewdudley

    ewdudley Minister of Fire

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    $350 including the 153 Mixing Setpoint Control?
  10. kuribo

    kuribo Feeling the Heat

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    No, that is just for the valve and actuator....Control is tbd....

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