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  1. #1
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    Question Chill Water Differential Pressure

    What do you guys think about installing a Differential Pressure close to the chilled water pumps rather than pick up a point through a second JACE where the existing DP is on the other side of a huge building.
    That would save any problems from losing a network connection that the current set up allows.
    Experience is another name for my mistakes.

  2. #2
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    They should have ran the wire to the controller, but as always some will cut corners.

    You can put it by the pumps, but you may run into issues with getting enough water at the ends of the system or running much higher than needed most of the time. DP should really be out towards the worst case branch which is typically near the end. A compromise might be use the one by the pumps with a higher setpoint using it only when the network craps out.
    Propagating the formula. http://www.noagendashow.com/

  3. #3
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    As orion suggested, use two. We have the remote dp reset the set point of the pump dp. If the network goes down, the pump maintains the last valid set point.
    UA LU 562

  4. #4
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    Install the DP at the pumps, note its reading while controlling to original. Setpoint should change to that reading when the network craps as the DP by the pumps will be much higher than the one out in the field. If you don't, the DP at the original location is going to be much lower and coils at the ends of the system will likely be starved. One would hope the network is fairly solid doesn't happen often so the issues cause without changing the setpoint might not be worth the hassle. None the less, if one is going to go through the hassle might as well try to make the best of it and do the added programming.

    Without PI valves, the whole balance depends on the existing DP sensor and maintaining the original setpoint at that location. Even with PI valves, most require a minimum DP to operate properly. If you don't maintain that setpoint at that point, toss the balance out the window.
    Propagating the formula. http://www.noagendashow.com/

  5. #5
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    Thread Starter
    The network is usually just fine. I noticed this after an upgrade was performed for the JACE's and original links were changed by the download.
    Just want to add a stopgap measure in case links (Niagara) were lost in the future.
    Considering having the PCG controller for the pumps to ramp VFD's to a nominal speed so Chiller would see flow and start until links re-established.

  6. #6
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    Another option is evaluate valve position to reset the plant DP setpoint. Make provisions so network trouble failsafes the DP to an acceptable level (maybe the last level).

  7. #7
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    Why bother with a DP controller close to the pump? Just have a default speed when the system goes down that is high enough to deliver a high percentage of design flow (probably 75 or 80%) and let the pump back up on it's curve until the system is back under control. Control close to the pump is going to have to deliver excess water anyway to assure the end coils are served.

  8. #8
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    Thread Starter
    Just had a meeting today with Mech contractor and the Controls vendor.
    They’re going to put in a 3 way valve, bypass loop and flow meter.

  9. #9
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    I take it someone finally realized that there was a need for minimum flow through the Chiller.
    Let us know how that works out. DP control of a Chilled Water loop without a Bypass usually makes the chiller unhappy.

    BTW, How you doing my friend ?
    If sense were so common everyone would have it !
    Stupid should Hurt !
    If people took care of their cars like they do their HVAC Systems you'd see a lot more people walking
    !

  10. #10
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    Thread Starter
    Doin’ ok, hows the new job?

  11. #11
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    It appears you have a constant pressure primary chilled water system. You do need to maintain minimum flow through the chiller but I would do it by controlling flow with chiller pressure drop.

  12. #12
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    Thread Starter
    Thanks for everyone's input!
    Experience is another name for my mistakes.

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