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Pump Location on a 3-Way Mixing Valve

Alan (California Radiant) Forbes
Alan (California Radiant) Forbes Member Posts: 4,170
edited January 2022 in THE MAIN WALL
When you do things wrong, hydronics can be very forgiving.


8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

Two btu per sq ft for degree difference for a slab
Solid_Fuel_Man

Comments

  • Jlinde37
    Jlinde37 Member Posts: 31
    I'm no expert but shouldn't the pump be pulling from the mixing valve?
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,170
    edited January 2022
    I'm no expert but shouldn't the pump be pulling from the mixing valve?
    Yes, it should, but it seems to be working alright as it's been this way for years.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • dopey27177
    dopey27177 Member Posts: 887
    Pump needs to pump to the 3 way valve.

    Jake
    Steam: The Perfect Fluid for Heating and Some of the Problems
    by Jacob (Jake) Myron
  • heathead
    heathead Member Posts: 237
    Sorry I don't understand is that thing under the yellow caution sticker a plate heat exchanger? Sorry Allen but can you explain the flow path. Thanks
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,170

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,092
    edited January 2022
    That's a strange configuration but I guess there's nothing wrong with it. Mixinging is 2 inlets and 1 outlet so it looks to me like it will work. I was confused but the piping on the HX. With Brazed plates are the in and out always on the same side and plate and frames they cross lile an X??
  • hot_rod
    hot_rod Member Posts: 22,814
    As Dan always teaches, what goes into a tee must come out of a tee.

    But with a 3 port fitting, how much goes which way. The path of least resistance thru the valve would see the most flow.
    Or is the least resistance thru the FPHX and into that port of the 3 way.
    Probably an un-predictable and very random temperature coming out?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    rick in AlaskaSolid_Fuel_Man
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,170
    Hot Rod: Do you think Julius Ballanco would know?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • hot_rod
    hot_rod Member Posts: 22,814
    Alan (California Radiant) Forbes said:

    Hot Rod: Do you think Julius Ballanco would know?

    PM magazine 2003 article that Siggy wrote about 3 way mixing valve Dos and Don'ts.

    In that application it looks like flow is going into A and B but also through some pressure drop in the plate HX on one side. It obviously works to some degree? So enough flow of mixed temperature is getting to the load. Has the system been doing its job? Comfortably? Your loads are fairly low in that climate so mis-piped systems may be more forgiving :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Alan (California Radiant) Forbes
  • Tom_133
    Tom_133 Member Posts: 904
    Alan

    You are not wrong with the forgiving hydronics. I told a customer who was getting 3- HTP 80 gallon tanks installed that piping the domestic water in a reverse return wont guarantee proper flow. Turns out based on the temp gauges I was wrong. That felt a bit like egg on the face. I know its not "right" but it works.
    Tom
    Montpelier Vt
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    I've seen that same mixer/pump configuration before as well. It was a new install done by the fuel company in press copper. It was a staple up radiant job, so I don't think they even needed any mixing. But it was working..... I kind of scratched my head too. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • EternalNoob
    EternalNoob Member Posts: 42
    The delta-p across the fphe might imbalance the MV enough to not mix properly. Or it might work just fine if the delta-p is not that significant. From a "pump the cold" standpoint it makes sense at least.

    Homeowners should know that there's always a big difference between "works" and "code" or between "works" and "best practice". Unvented DWV plumbing can work just fine, until it doesn't, not to code. 2x6 joists for a 2x8 span works fine, not to code. Strange that there are no building codes for radiant. Codes and inspections could improve the industry some day, clean up messes and actually make installer's jobs easier in the long run. When I've had radiant installs inspected the only thing they ever look for is a pressure test on the pex and the presence of a back-flow-preventer. I'd also have to admit that i've done plenty of "works" but not "best practice" things, and looking back would have rather had an inspector catch my mistakes.

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