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Primary/Secondary piping

duffy_4duffy_4 Posts: 64Member
Does it make a difference when piping a mod con boiler with multiple zones and using pri/ sec piping and closely spaced tees as your hydraulic separation in lieu of a hydro separator ,if you pipe the sec circuits out of the branch of the tee s,and have the pri circuit thru the run of the tee s, instead of having the primary piped into the branch of the tees,does the system operate different each way .thanks


  • duffy_4duffy_4 Posts: 64Member
    pri/sec example

    example of sec piped out of branch of closely spaced tees,only one zone,thought i might be able to pipe direct to manifold from tt 110,but didnt want to have any flow issues
  • Chris_110Chris_110 Posts: 3,056Member

    A LLH provides you protection of the hx, acts as both an air and dirt separator as well as stops temp drops across zones as multiple zones open. Here is a nice read published quite some time ago.

    By the way, your piping is wrong.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • duffy_4duffy_4 Posts: 64Member

    Chris why is it wrong,I have all the idronics books from caleffi on page five figure 3 of that link u sent me is the piping I used on above job,I have used the hydroseperators on numerous jobs,my question was if it makes any difference hydraullically with the two different piping orientations ,thanks
  • Chris_110Chris_110 Posts: 3,056Member
    100% Correct

    The system side piping is correct as shown in figure 3. Boiler side isn't...Please see attached.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • duffy_4duffy_4 Posts: 64Member
    Pri sec

    Look at page 12 and 13 of link u sent it has drawing of same piping I used ,again I would like to know the difference if ant of both ways op piping,if sec has greater flow req that primary thanks
  • SlimpickinsSlimpickins Posts: 320Member
    edited May 2012
    piping is ok

    I'm not an engineer, just a boiler tech with almost 30 yrs of experience but I think you're ok on the piping. Although not the way TT recommends in their drawings it should be just find. In fact, when NYThermal came out with their Trinity T series, this was how their schematic in the installation manual was drawn and it required much more flow than the Prestige. The engineer from TT told me that the 110 only needs 2.7 gpm at high fire so I think you're good. If in doubt, get a hold of TT technical department and shoot them a pic and see what they think. In the future, always best to go with the manufactures recommended piping. I'd rotate the cartridge of the secondary pump so the junction box isn't on the bottom.

    BTW, the 110 seems oversized if thats the only load you have.
  • duffy_4duffy_4 Posts: 64Member

    thanks slim, i rotated cartridge after pic taken good eye,i know tt goes to high fire for first two minutes before it modulates so was trying to keep adequate flow thru it by going pri/sec,boiler sized for dhw load as homeowner wants to add 80 gal indirect down the boiler ops fine and have had no problems. i usually use hydro seperators when i have more zones and loads,am currently working on similiar job as this except it has another small hydronic zone {master bath 100 sq ft] and thinking of using small 6 gal electric hwh as a buffer tank/seperator/air elimination
  • Chris_110Chris_110 Posts: 3,056Member
    Couple Of Concerns

    The spacing in those tee's look like they are more then 4 pipe diameters apart and not much straight pipe exiting the tee heading into the boiler. Another concern I have is delta-t between boiler supply and return.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • NRT_RobNRT_Rob Posts: 1,009Member
    2.7 GPM

    is a low fire, not a high fire flow rate. at high fire that'd be something like a 75 degree dt. on low fire it's just over 20.

    as for the original poster, I reject that there is much appreciable difference between hydro separators and closely spaced tees. the amount of/quality of mixing at the tees may vary somewhat, and you get BETTER hydraulic separation with a hydraulic separator... as well as the air and dirt separation point... but from a flow perspective, p/s works fine.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • duffy_4duffy_4 Posts: 64Member
    pri/sec using small buffer tank

    would the following schematic provide adequate hydraulic seperation and help alleviate what i think might happen if i just use closely spaced tee s and the small zone for the master bath is calling for heat [that the boiler would short cycle on and off rapidly].any problems seen with this piping,would be using alpha pump or b&g new pump for sec pump.where is best place to tie in fill valve .thanks for your input much appreciated.vincent
  • SWEISWEI Posts: 7,356Member
    a small buffer tank

    Makes a fantastic hydraulic separator, and would reduce your cost (both CapEx and OpEx) by eliminating a pump.  If you have zone valves or TRV's, then a smart pump on the secondary will be perfect.

    I'm not really a fan of auto-fill valves on closed loop hydronic systems.
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