How to automatically vent domestic hot water recirculation loop

Discussion in 'General Plumbing Help' started by Greenthorn, Nov 11, 2018.

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  1. Nov 18, 2018 #41

    frodo

    frodo

    frodo

    Just call me Macgyver Professional Supporting Member

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    after the circ line leaves the mech room where does it go?
    I am wanting to know
    1] how it ties in at the end of the run
    2] what changes of elevation does it make?
    3] fittings and valves in system
    I am concerned that your pump only has a 3' head listed.
    I see more than 3' 9'' of head in the mech room. and the water still has 50' to travel
    I am concerned you do not have enough head pressure in that pump to circ the water
    so ..in theory,, the water is not circulating it is sitting static

    Features

    • Silent operation
    • Integrated external sensor cable - simply mount the sensor on the hot water supply pipe
    • One-touch operation - settings are easily changed using only the fingertip
    • 6 feet line cord
    • Insulation shells for fast installation
    • Lead free brass housing eliminates risk of corrosion
    • Compact design facilitates installation in confined spaces
    • Maximum flow 2.2 GPM (0.5 m³/h)
    • >>>>>>>>>>>>>Maximum head 3.9 ft (1.2 m)<<<<<<<<<<<<<<<
    • Liquid temperature 36°-203°F (2°-95°C)
     
  2. Nov 18, 2018 #42

    RenewDave

    RenewDave

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    Taco 400 auto air vent. Replace the uppermost 90 above the pump and boiler drain with a tee. The Taco 400 is 1/8 inch threads, adapt to that and purge the system and you’re good. A lot of people don’t have vents on their loops and they work. I would like to figure out why you’re getting this problem uniformly every 10 days.
     
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  3. Nov 18, 2018 #43

    Greenthorn

    Greenthorn

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    Correct me if I'm wrong, but I think the head loss calculation doesn't include the heights in a recirculation loop but only the lengths, fittings, pipe material and diameter. Without getting into all the nitty gritty, I will make the claim that both in theory and in practice, the head loss is not an issue.
     
  4. Nov 18, 2018 #44

    Greenthorn

    Greenthorn

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    Thank you chiming in, RenewDave. Do you think installing the vent at the elbow you mentioned is a better idea than, say, somewhere on the horizontal run in that same high region of the loop, maybe near the ball valve?
     
  5. Nov 18, 2018 #45

    Greenthorn

    Greenthorn

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    Here is a fitting that could save some transitions and maybe connect directly to the vent.
    Vent Elbow.jpeg
     
  6. Nov 18, 2018 #46

    Diehard

    Diehard

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    True! The only head loss in a closed loop piping system would be the friction loss. Sort of part of the reason it is referred to as a "circulator".

    Assuming the valves near the pump, you mention, are the 2 globe valves for the 2 recirc loops, that sounds good provided you shut off the ball valve located on the discharge side of the pump to isolate the cold water from running back. A garden hose should be connected to the draw-off valve to properly purge the each of those 2 loops. i.e. one globe valve open at a time.(although I thought one of those 2 loops was not completed.)
     
  7. Nov 18, 2018 #47

    frodo

    frodo

    frodo

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  8. Nov 18, 2018 #48

    Mr_David

    Mr_David

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    I was trying to follow the thread but the photo posted in #1 post shows as a link to another thread about a chrome p-trap. ???????

    IMG_7691.JPG
     
  9. Nov 18, 2018 #49

    Diehard

    Diehard

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    It's a closed loop while it's circulating back to it's source.
    Sure when a sink faucet is open, any air that can reach the faucet would come out, however, as we know we have at least one example, at the water heater, where an air trap was created after the pump, by going up, to the right and then down again. Kinda like the same reason an air vent(manual) is recommended at the return side of baseboard water heating systems.

    In terms of head requirements of the pump, it should not have to overcome any elevation head. Just look at it as creating a differential between the suction side and the discharge side of a pump that's located within a 70 psi hydraulic system.
     
  10. Nov 18, 2018 #50

    Diehard

    Diehard

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    Just looked at that link you provided on the grundos pumps. page 40.
    Pretty much confirms what @Greenthorn had said,,,
    "The pump uses two temperature sensors, one within
    the pump and the other connected to the pump by a
    cable installed on the hot-water flow pipe."

    It's just too bad it doesn't explain the philosophy behind it.
     
  11. Nov 18, 2018 #51

    Diehard

    Diehard

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    That is weird!
    This is what we see when we click on it.
    IMG_6799.jpg

    I'll bet you're using a cell phone.:confused:
     
  12. Nov 18, 2018 #52

    Diehard

    Diehard

    Diehard

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    You'd be better off with this one. Should be able to screw the auto vent directly instead of having to add a coupling.

    3/4 in. x 1/8 in. x 3/4 in. Forged Bronze C x F x C Baseboard Tee
    everbilt-tees-wyes-c705lfhd341834-64_1000.jpg
     
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  13. Nov 19, 2018 #53

    Greenthorn

    Greenthorn

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    Frodo, better sources such as the Caleffi videos previously mentioned will describe head loss/friction in better detail, but the way I think of it is: yes, you have to pump the water uphill, but you get all that energy back when it comes back down the hill, minus friction. Also, the vast majority of the time the faucets are closed and so any detailed calculation of head loss just considers the faucets as some fitting with some equivalent length of pipe as a factor.
     
  14. Nov 19, 2018 #54

    Greenthorn

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  15. Nov 20, 2018 #55

    Mr_David

    Mr_David

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    yes I was and thanks for the photo.
    P.S. Now I'm going to check the #1 post and see what's there
     

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