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  1. #1
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    Approach Temperature of Cooling Tower

    Approach Temperature is the temperature difference between the temperature of the cooling water leaving the cooling tower and the wet bulb temperature of the air entering the cooling tower

    I would like to seek someone help whether high approach temperature can optimize the power consumption of variable speed cooling tower.

  2. #2
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    I am sure it would reduce the power consumption of the cooling tower, but it would be at the expense of the ACs being served. Not a good idea.
    "I have never let my schooling interfere with my education."
    Mark Twain
    NEVER STOP LEARNING.

  3. #3
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    Thread Starter
    Thanks for your swift reply

    Would you mind telling more about the expense of the ACs being served?

  4. #4
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    Higher tower temps mean higher compression ratios

  5. #5
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    Quote Originally Posted by pecmsg View Post
    Higher tower temps mean higher compression ratios
    And the fan motor HP is much less than the compressor HP. Thus it is a win little, lose big situation.
    "I have never let my schooling interfere with my education."
    Mark Twain
    NEVER STOP LEARNING.

  6. #6
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    Thread Starter
    Thanks Reply

    Would you mind telling me more details with an example why high approach temp will lead to high compression ratio and compressor HP? Thank You for help.

  7. #7
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    I would say that warner tower water, raises the condensing temperature and pressure. If the suction side stays the same, the high side pressure increases and thus the compression ration (condenser psia/suction psia) also increases.

    The compression ratio is simply the ratio of the absolute discharge pressure to the absolute suction pressure.

    Because most gases increase in temperature when they are compressed, the final compressor outlet temperature is always a concern. A high discharge temperature can lead to the failure of internal components due to material degradation or excessive thermal expansion. Compression ratio is also important in determining required horsepower; the higher the ratio, the greater the required horsepower for that stage.https://www.pumpsandsystems.com/topi...-ratio-matters
    "I have never let my schooling interfere with my education."
    Mark Twain
    NEVER STOP LEARNING.

  8. #8
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    Something being overlooked here is that your equipment was designed for a given tower temperature range. If you have a chiller attached to this tower, you can have negative side effects of tower water that is too cold as well as too high.

    Before you start messing with your tower, consult your chiller or heat pump loop tech to find out what the design temps and optimum operating temps are for the system. The tower isn't your big energy eater in the system. If you are messing with it in the name of energy, you could be wasting quarters to save pennies. Fan VFDs that are driven off of loop temp can be beneficial, as can pump VFDs that are driven by a flow meter, but be very careful on the pump side as low flow to a chiller can be very costly.

    The design parameters of the terminal equipment should always dictate the performance of the cooling tower.

  9. #9
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    At the chiller plant I supervised for almost a decade, I programmed a tower supply temp reset via design wet bulb. But, I found that when wet bulb temps were at or near design for the tower (78 wet bulb, 85 supply water from tower for a 7 degree approach) that the chillers would either surge or be dancing on the verge of surge. Turns out 19XR chillers really don't like entering condenser water temps much warmer than 82 degrees.

    Which, for the OP's topic, reinforces the notion that plant optimization is definitely plant specific; there are no boiler plate optimization schemes that can wholly be applied to every plant out there.
    Building Physics Rule #1: Hot flows to cold.


    Building Physics Rule #2:
    Higher air pressure moves toward lower air pressure


    Building Physics Rule #3:
    Higher moisture concentration moves toward lower moisture concentration.

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