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Secondary pump to mix on large residential boiler

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Radiant23
Radiant23 Member Posts: 26
Hello,

I recently changed a Weil Mclain 299 boiler, and saw something I do not see. It had primary secondary piping off the boiler, with a tap for an indirect tank. The primary secondary tees connected to the bull of the tees, but then the supply line is piped in 2”, and is piped with another 0014 taco pump to circulate through a loop, 4 elbows to make a loop. The supply taps come off the loop and pump off of that. I am pretty sure the second pump is just used to mix the water around the 2 inch copper loop to balance out temperature so all pumps get a fairly similar temperature. I am correct in thinking this, and if so, is there a method this is called. Application is staple up radiant for the whole system with an indirect.

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  • Radiant23
    Radiant23 Member Posts: 26
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    Here
  • Radiant23
    Radiant23 Member Posts: 26
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    The pump that I am thinking is mixing is the pump on the bottom right corner.
  • hot_rod
    hot_rod Member Posts: 22,158
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    18 circulators on a 299 boiler? probably don't even need to fire the boiler on mild days :)
    That is a complicated piping, for sure.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mad Dog_2
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,965
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    Very neat...gotta give em that!  Mad Dog 🐕 
  • hot_rod
    hot_rod Member Posts: 22,158
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    I can't see enough piping on the left of the boiler to see how the loop, closely spaced tees, and the big pump header all tie together. Or a pump on the closely spaced tee bridge?
    A drawing may be better.

    But it looks like too many pumps for what is going on?

    Does it work properly?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Radiant23
    Radiant23 Member Posts: 26
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  • Radiant23
    Radiant23 Member Posts: 26
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    No issue with operating, just curious if this method had a name. It is hard to see from pics…

    boiler pipes from S & R into a second loop, the 2” on the wall. There is a tap for domestic indirect, but not an issue. 

    From there it tees into the 2”, tees spaced about 3” away from each other, think it would be better to be a little further apart. 

    That 2” loop goes as follows from the supply tee mentioned above. From left to right the water is pulled out of right side of supply primary tee by a 0014, it then goes past an air scoop with 1/2” make up water going into the bottom. Next it pipes into the right side run of the secondary header supply tee. About 3” after this tee is the return tee run from the secondary header. The secondary supply and return come out of the bill of those two tees. From there it continues back to the left side run of primary tee and the loop continues. 

    I have the 0014 on whenever any zone calls for heat. Pretty sure this is just mixing all of the water And expands the amount of heated water to reduce short cycling of the boiler. Some of the secondary pumps goes to a onix manifold, with anywhere from 2-8 taps, say 4 is about average. Others go to a field built manifold with 2-5 Honeywell zone valves. Was going through and finding all of the hidden manifolds and zone valves, labeling it all up for ease of service later. Jumping out stats that weren’t making calls. Some of these loops might travel 200’ to get to a 40 sq’ bathroom zone. Overkill maybe, but great control. Even with those small zones on, it seems like boiler will come on, hit aquastat temp, turn off but that 2” manifold will have some stored temp to keep boiler off longer then something not piped this way. 
  • hot_rod
    hot_rod Member Posts: 22,158
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    Seems like using 2" copper and press fittings for a few gallons of buffer is fairly expensive?

    Plus flow velocity could be below 2 fps in that large diameter tube? You need at least 20 gpm in 2" copper to get to 2 fps.
    I suppose you could calculate the added water volume with all that 2" copper.

    At least the boiler space should stay warm with all that copper piping :)

    If it works, so be it.

    I'm not a fan of copper into galvanized fittings? But I know some Weils have galvanized nipples coming out of the top of them. Odd?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • GroundUp
    GroundUp Member Posts: 1,909
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    This isn't uncommon. It's often used for systems with differing temps and flow rates for the reason you mentioned. I refer to that central loop as an "intermediate loop", but I think I made that up in my head lol.
  • GroundUp
    GroundUp Member Posts: 1,909
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    This isn't uncommon. It's often used for systems with differing temps and flow rates for the reason you mentioned. I refer to that central loop as an "intermediate loop", but I think I made that up in my head lol.
  • hot_rod
    hot_rod Member Posts: 22,158
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    Whenever you pipe closely spaced tees you will get temperature blending. If you knew the flow rate of the boiler circ and the circ going to the zone circ manifold you could predict temperature being sent to the system.

    Every time a zone pump turns on the temperature blend will change across the #2 set of closely spaced tees. So somehow you must measure temperature at the zone pump header and the boiler constantly adjusts it's SWT?, based on the changing flowrate of the 15 zone circs.

    Since you are blending at the tees, you are probably running the boiler SWT much higher that the zones require?

    Here is an example of the mix temperature formula used when two different flows blend at the closely spaced tees.

    This book does an excellent job of explaining the temperature blending in P/S systems
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Radiant23
    Radiant23 Member Posts: 26
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    Thanks for all the input. I’ll look at the info. 
  • Alan (California Radiant) Forbes
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    I don't see any closely spaced tees on the tertiary line. All zones are the same temperature.


    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
  • Radiant23
    Radiant23 Member Posts: 26
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    Yes. All zones same temperature 
  • hot_rod
    hot_rod Member Posts: 22,158
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    All the zones would see the same temperature if piped across a properly sized header, sized for total flow of all those zone circs, ideally a 2 fps velocity. Fig 7-12b

    As I see it is is piped more like 7-6a or 7-7a?

    Idronics 19 talks about some of the creative P/S piping and potential drawbacks

    https://www.caleffi.com/sites/default/files/media/external-file/Idronics_19_NA_Proven hydronic distribution systems.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream