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Thread: Surging.

  1. #14
    Join Date
    Nov 2006
    Location
    North Carolina
    Posts
    130
    Shophound,

    Could you go into a little more detail on the wet bulb reset schedule for the ecwt. I have never thought about doing this, sounds interesting.

    Thanks
    Chad

  2. #15
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    Quote Originally Posted by chad_nc View Post
    Shophound,

    Could you go into a little more detail on the wet bulb reset schedule for the ecwt. I have never thought about doing this, sounds interesting.

    Thanks
    Chad
    I wrote a program in my building's automation system (Metasys) to reset the ECWT to be seven degrees above the wet bulb temperature of the air entering the towers. Seven degrees happens to be the design approach temperature of my towers; others might vary.

    How it works is thus: I have a temperature and humidity sensor out in the cooling tower room. It feeds both readings to the Metasys, which then converts this data to wet bulb temperature. That number then runs through a program that links to the ECWT set point. As the wet bulb temperature drifts up or down, the ECWT is reset accordingly. Within the program is an upper and lower limit, so the towers are not run too warm or too cold. I also added a bit of buffering to reduce constant resetting of the ECWT set point due to fluctuating wet bulb temperatures.

    NOTE: I could do this because my towers have VFDs on the blowers. The McQuay Chiller Plant Design Guide also discusses the wet bulb reset strategy as one method used for optimizing chiller plant operations. This guide is available on the internet.

    Here's a screen shot of the logic (if the attachment works):
    Attached Files Attached Files
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #16
    Join Date
    Nov 2008
    Posts
    366
    Chad NC

    You may be interested in this as well.

    CTV-EB-84[1].pdf

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