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  1. #1
    Join Date
    Jan 2002
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    Fort Worth\Dallas, Texas
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    1,708

    Cooling Tower Optimization

    Im curious how many people are doing tower optimal control, and for those that are what strategies are you using?
    Go Rangers!

  2. #2
    We do this alot. We control tower fan speed to maintain a calculated CWFT setpoint. CWFT setpoint is calculated based upon outside air wetbulb + an approach temperature of something like four degrees. Need to set limits on the setpoint based upon chiller information, a common low end is 65 degrees.

  3. #3
    Join Date
    Jan 2002
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    Fort Worth\Dallas, Texas
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    1,708
    Thanks for the info Travis.
    Go Rangers!

  4. #4
    Join Date
    Mar 2005
    Location
    Pacific Time Zone
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    4,224
    Doing a similar thing - only when you have everything with Econo-coils you can run the loop a lot cooler.

    BTW - Is CWFT - Condenser Water Fan Temperature Setpoint?
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  5. #5
    Join Date
    Apr 2007
    Location
    San Diego, CA
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    1,348
    Quote Originally Posted by crab master View Post
    Doing a similar thing - only when you have everything with Econo-coils you can run the loop a lot cooler.

    BTW - Is CWFT - Condenser Water Fan Temperature Setpoint?
    Maybe Condenser Water From Tower? as opposed to CWTT

  6. #6
    Join Date
    Sep 2004
    Location
    SoCal
    Posts
    449
    We like to control tower fan speed from head pressure inputs to a PI control loop. We have a building that includes a 300 ton evap condenser with 2 separate DX refrigeration circuits. Pressure transducers installed on the liquid line are wired to a couple Circon GPC controllers which send the values to an iLON which selects the highest signal and transmits back to the Circon controller. The GPC controller uses a PI function and sends the speed signal to a Yaskawa VFD that has a LON card installed. It works really well and holds head pressure on mild days within +/-5 PSI of setpoint.

    Recently we added a flow meter on the makeup water line and added the makeup water flow gpm to the network. We log the data every 15 minutes and were amazed when there were a few days this summer where the tower consumed close to 5,000 gallons of water a day! We can also detect if the float valve leaks during shut-down hours. Next phase will be to add TDS and PH sensors.
    Cheers,
    lb
    A hundred million nodes - it's a LON story.

  7. #7

    Optimization?

    Quote Originally Posted by tshort View Post
    We do this alot. We control tower fan speed to maintain a calculated CWFT setpoint. CWFT setpoint is calculated based upon outside air wetbulb + an approach temperature of something like four degrees. Need to set limits on the setpoint based upon chiller information, a common low end is 65 degrees.
    That's not really optimization though, is it? More of a strategy, but it doesn't really optimize the system.

    Trane has a strategy, and I could tell you what it is, but then I'd have to kill you.

  8. #8
    Quote Originally Posted by lonboy View Post
    We like to control tower fan speed from head pressure inputs to a PI control loop. We have a building that includes a 300 ton evap condenser with 2 separate DX refrigeration circuits. Pressure transducers installed on the liquid line are wired to a couple Circon GPC controllers which send the values to an iLON which selects the highest signal and transmits back to the Circon controller. The GPC controller uses a PI function and sends the speed signal to a Yaskawa VFD that has a LON card installed. It works really well and holds head pressure on mild days within +/-5 PSI of setpoint.

    Recently we added a flow meter on the makeup water line and added the makeup water flow gpm to the network. We log the data every 15 minutes and were amazed when there were a few days this summer where the tower consumed close to 5,000 gallons of water a day! We can also detect if the float valve leaks during shut-down hours. Next phase will be to add TDS and PH sensors.
    Cheers,
    lb
    Quick question - is this being done on a chilled water plant with centrifugal compressors? I think that you would end up with a lot of surging.

  9. #9
    Join Date
    Sep 2004
    Location
    SoCal
    Posts
    449
    Quote Originally Posted by SubCoolWasTaken View Post
    Quick question - is this being done on a chilled water plant with centrifugal compressors? I think that you would end up with a lot of surging.
    No, this is a DX plant with (2) Carrier 5H120's. On another job we did similar head pressure control of tower fans with a Carrier Screw 30GT chiller running R134A equipped with LON translator card. Discharge pressure from the chiller was sent onto the network and a freely programmable LON device did the rest.

    At the end of the day, it's the head pressure that counts! Not too high and not too low!

    Cheers,
    lb
    A hundred million nodes - it's a LON story.

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