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Mixing valve question.

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icy78
icy78 Member Posts: 404
Got a service call for nursing home bath area is cold. In.floor pex. Asse 1016 T mixing valve. Taco 007 circ. B n G flow control SA 3/4. Tstat is t87 way off level. Fixed that. Pump starts running. 0.7 amps. Pump inlet warms to 93f so I thought o.k. might take a while for the floor to warm up. So today it hasn't warmed up. Main loop is at 148f but out at bath loop it's 113 before mixing valve and 93 after valve. I jack up the boiler temp just to see what happens and bath loop feed goes up same amount and mixing valve is feeding 105f. MY questions are: how does this valve mix 60 psi cold water with 25 psi hot water? And is there a way for me to know what the flow rate is? Isolaton valves were not installed on this 20 years ago so not so easy to pull apart. Also no one knows how this used to work because all new people on site. ( by that I mean that no one knows if boilers were running 160- 180 water before to satisfy the bath loops or if the reset I put in the new Tekmar is too low. 180 at 15f OSA temp and off at 70 osa temp.) Boilers off all summer did not generate a cold floor complaint.

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  • kcopp
    kcopp Member Posts: 4,448
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    Different pressures will not work well w the mixing valve. Is the circulator pulling the water out of the valve or is it pushing in? Needs to pull/suck out.
  • icy78
    icy78 Member Posts: 404
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    Thanks. Yes the pump pulls 12" from the mix valve and pushes 12 " to the flow control. Now it's 140f at the hot inlet to mix valve and 50f on the cold. Mixed is 105 with mix valve wide open. Mix Valve highest setting is 120f. I could see the unbalanced pressures not allowing 120f out of the valve I guess. I'M thinking that if flow was low thru the loop that then I may see 120f at mix valve outlet, but with perhaps normal flow it won't get there unless inlet temp is higher like 160f? OR mix valve is dirty or restricted?
    Zman
  • Zman
    Zman Member Posts: 7,605
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    Can you give some specifics on the model of the mixing valve and how that loop is piped? How big is the area and how many loops.

    The valve does not mix in new cold high pressure water, it just recircs some of the return water from the loops..


    I am guessing the boilers are atmospheric non condensing. If so the temps you are running are too low. The tekmar should have a setup where you can measure return water temps and automatically prevent flue gas condensation. Return water temps should exceed 140 to prevent condensation.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • icy78
    icy78 Member Posts: 404
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    It's probably piped wrong then . I traced the cold line to domestic cold water. ONE loop. Room size is 15 by 10 but it may only do 1/2 of that.
  • icy78
    icy78 Member Posts: 404
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    Here's some pics.
  • Zman
    Zman Member Posts: 7,605
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    icy78 said:

    Here's some pics.

    Did not come through...
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • icy78
    icy78 Member Posts: 404
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    Try again.
  • hot_rod
    hot_rod Member Posts: 22,468
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    How is it that you gave widely varying pressure in hot to cold side? Are there different sources for hot and cold?

    TMV should not exceed a 2:1 pressure difference from h to c.
    also they like to have at least a 20 degree between hot supply and mix outlet, to control accurately

    1016 is a point of use valve and will not adjust above 120 F

    It is probably a low Cv also, but should handle a small zone gpm

    These Valves are prone to sticking in dirty fluid or hard water conditions. Disassemble and clean or replace the cartridge
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • icy78
    icy78 Member Posts: 404
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    Can't get them to post. Flow control is BG 107034. Valve is Watts asse 1016 type T. PUMP 007-f5.
  • icy78
    icy78 Member Posts: 404
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    Hotrod. (Seems I can't quote either). Maybe because I'm on a mobile device? Anyhow, Hotrod yes, cold is piped to domestic, and hot to boiler. I suspect that the original Tekmar that took an electrical hit, had much higher set points than I put in the replacement. I will raise the boiler setpoint somewhat and find valves somewhere to isolate and clean the mix valve. ( 5 Weil McClain gv boilers on staged, rotating start.)
  • hot_rod
    hot_rod Member Posts: 22,468
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    Heating a tile floor should not require very high supply temperature, depending how toe tube was installed?

    If the system has worked well in the past, I would suspect a dirty or scaled valve, or failed heat "pill" inside
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    icy78
  • icy78
    icy78 Member Posts: 404
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    Thanks guys. You made me look smarter than I am! Anyhow the maintenance guys will pull the valve and clean it. I guess I'll go back if they have issues after that.
  • icy78
    icy78 Member Posts: 404
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    They finally did the work. It was a "bad" mixing valve.
  • Dave H_2
    Dave H_2 Member Posts: 558
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    Wait, if I read this thread right, you are saying that the "cold" on the mixing is coming from the plumbing system and the "Hot" on the mixing valve is coming from the heating system?

    If that's right, then it is piped wrong and will never work.

    The "cold" comes from the return from the radiant floor and then blends with the "hot" supply from the heating plant. The radiant system is a closed loop system so you cannot put cold water from the plumbing into a closed system. That would mean that water would have to leave the system.

    See the attached

    Dave H.
    Dave H
  • icy78
    icy78 Member Posts: 404
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    I'd have to agree. However, the domestic cold line does tee into the cool return side before the mixing valve. I can only say that they changed the valve and now the floor is warm! It's been a while and I'm fuzzy on it! I guess in theory the cold 60 psi should then fill the hot side to 60 psi so maybe there's a check valve I missed. There's some odd piping in the building. 50 years old with many changes. Recently I was there on a patient room baseboard that it seemed no one could get to work. It had a simple Taco zone valve that was open . I traced pipes and way down the end of the hall, fifty feet away, I found a valve closed on the return line. 18 inches away another valve closed on that same pipe, and they had been like that for who knows how long. The maintenance guy was stumped and said no one had been up there above that ceiling for years.! It was just the right length of pipe for a pump to have been installed at some point.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    I sure hope this isn't some weird open system configuration. W/O pics or diagram we can't tell.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • icy78
    icy78 Member Posts: 404
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    As I ponder this 2 months later I see that I must have traced the piping back on the cold side incorrectly and it actually went to the boiler return. What nags at me though is the boiler return was only 20ft away out in the hall and this cold pipe was easily followed for 100 feet to close to the boiler room at which point I could've lost it, crossed it. But why not connect at the return in the hallway? May never know but I'd sure like to!