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DeltaT vs DeltaT, large building/ condensing boilers/ FCU with zone valves

Jeff Elston
Jeff Elston Member Posts: 289
edited July 2015 in THE MAIN WALL
Opinions please, as if there are not enough already! haha!

Please I am looking for real world experience here.

Building is 275 apts. each apt has FCU's. typically 3-4 per apartment. A total of 1144 FCU.
20 floors.
duel temp system building has 2 loops (2) w/ vfd pumps
6- FBN2000 w/ Viridian pumps VR20 set at a 40* deltaT.

Building loops and boiler loop are coupled with a 5910 flex balancer plus.
All FCU units have zonelves top floor has 3- way zone valves.

Killtec BMS controls chiller and the 2 building loop pumps both vfd.
When the building is in cooling mode the building loop pumps run on Delta P.

What would make the best sense in terms of efficiency in setting up the building loop pumps during heating mode Delta P or delta T?

Thanks in advance!

Please ask any questions no problem.


  • Jeff Elston
    Jeff Elston Member Posts: 289
    I am alone in this world.
  • JStar
    JStar Member Posts: 2,752
    edited July 2015
    I could give you my answer, but there a much smater hydronic men on this forum. I would wait for their response.

    @hot rod rod @Mark Eatherton
  • hot_rod
    hot_rod Member Posts: 14,552
    No actual experience, but from what I have read and researched, the delta P works well with a ZV system.

    So the upper level has a 3 way ZV for bypass function, but no bypass on any others?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jeff Elston
    Jeff Elston Member Posts: 289
    nope, also we don't know the exact pipping layout,,,,what is behind the walls is just that, and I am not Superman so no xray vision
  • hot_rod
    hot_rod Member Posts: 14,552
    That's perhaps the toughest job. Large, unknown piping and control valves.

    I do like the Grundfos Magna for these as it shows a graph on the screen of the pump control of the system and where the pump is running on the system curve. So you can dial in the pumping side, once the pump develops a "fingerprint" of the system.

    Even if you could find an original design, things change over the years are various contractors try different repairs.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
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