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  1. #1
    Join Date
    Mar 2011
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    Los Angeles, CA
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    VFD on condensor side?

    would you recommend staging the condensor loop of a chiller with cooling towers? the evaporator side is staged with two 600 ton and 200 ton chiller and three pumps.

  2. #2
    Join Date
    Jan 2009
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    Not in Iran
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    1,107
    Lilttle confused.!'?,!'s

    Maybe a drive on the tower.,

    Primary, secondary.,
    Variable primary?

    Fill us in.

    Don't understand the (staging of cond loop)
    Keep the enter and leaving water temp in spec range
    no signature blast'em man blast'em
    !!!KILL THE TERRORIST!!!

  3. #3
    Join Date
    Dec 2008
    Location
    Dixiana, AL
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    You're going to have to explain yourself a little better than that or folks are just gonna be guessing at what you're trying to accomplish.

  4. #4
    Join Date
    Mar 2011
    Location
    Los Angeles, CA
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    My apologies for being unclear.

    The chiller plant is composed of two 600 ton and a 200 ton chiller. They are running three pumps on the evaporator side, two of them are 1120gpm and one is 600gpm. The smaller pump is for the small chiller.
    There are three condensor water pumps with 1950gpm capacity. I am wondering why they are not providing a smaller condensor water pump for the smaller chiller? Assuming that the smaller chiller is operating at 50tons, the 1950gpm pump would be pumping roughly about 150gpm. I assumed 3gpm/ton.
    The pump is a VFD and it can module down to a lower flow. But operating it 150gpm would destroy the pump!?

  5. #5
    Join Date
    Oct 2011
    Location
    La.
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    282
    The smaller pump still needs to pump 600 GPM as the small chiller is 200 tons. You do not lower condenser water flow unless you do not like your condenser tubes. Trane tries to sell less condenser water flow, but you need a certain water velocity to keep tubes from fouling.

  6. #6
    Join Date
    Dec 2008
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    Dixiana, AL
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    Why would operating it at 150 gpm necessarily destroy the pump? And why throttle the pump down to match the tonnage exactly? Hold the leaving temp down, hold the condenser pressure down, take the horsepower requirements down on the compressor - there's your energy savings. Understandably you wouldn't pump 1950 gpm thru a 200 ton condenser, but turn it down to 600 gpm and let it fly.

  7. #7
    Join Date
    Mar 2011
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    Quote Originally Posted by klove View Post
    Why would operating it at 150 gpm necessarily destroy the pump? And why throttle the pump down to match the tonnage exactly? Hold the leaving temp down, hold the condenser pressure down, take the horsepower requirements down on the compressor - there's your energy savings. Understandably you wouldn't pump 1950 gpm thru a 200 ton condenser, but turn it down to 600 gpm and let it fly.
    According to the sales rep, operating the pump at 150gpm would heat up the motor and reduce its life. But what you said makes sense. I can keep the gpm at 600 and avoid fouling. And compress my ref to a lower pressure. Would that be a function of the chiller control system?

  8. #8
    Join Date
    Jul 2006
    Location
    The Great country of Texas
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    429
    The problem with going down to 150 gpm is the amount of flow over the tower. You may not get the evaporation rate you need over the tower. Rule of thumb is 50% flow over the cell of the original selection which in your case would be 975 gpm
    "I'm from Texas, what country are you from?"

  9. #9
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    Dec 2008
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    Dixiana, AL
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    Quote Originally Posted by Saman1366 View Post
    According to the sales rep, operating the pump at 150gpm would heat up the motor and reduce its life. But what you said makes sense. I can keep the gpm at 600 and avoid fouling. And compress my ref to a lower pressure. Would that be a function of the chiller control system?
    Your earlier post said the low flow rate would destroy the pump, didn't say anything about the motor. Not having the pump curve, there was no way to know the turndown on the pump. Most motors will run very well down to 15 hz, some much lower, so I'd have to see the pump curve to speak intelligently about that aspect.

    My question to your question is "Would what be a function of the chiller control system"?

  10. #10
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    Jun 2010
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    U.A. (upper Alabama)
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    Quote Originally Posted by klove View Post
    My question to your question is "Would what be a function of the chiller control system"?
    And my question is, how do you compress refrigerant to a lower pressure?

  11. #11
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    Mar 2011
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    Los Angeles, CA
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    Quote Originally Posted by klove View Post
    Your earlier post said the low flow rate would destroy the pump, didn't say anything about the motor. Not having the pump curve, there was no way to know the turndown on the pump. Most motors will run very well down to 15 hz, some much lower, so I'd have to see the pump curve to speak intelligently about that aspect.

    My question to your question is "Would what be a function of the chiller control system"?
    How would the chiller know when to lower the condenser temp and pressure? Is that something that comes with the chiller control system? Ill get you that pump curve.

    Quote Originally Posted by stickerhead View Post
    The problem with going down to 150 gpm is the amount of flow over the tower. You may not get the evaporation rate you need over the tower. Rule of thumb is 50% flow over the cell of the original selection which in your case would be 975 gpm
    Shoot..I wasn't thinking bout the cooling tower.

  12. #12
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    Mar 2011
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    Los Angeles, CA
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    Quote Originally Posted by cperk View Post
    And my question is, how do you compress refrigerant to a lower pressure?
    VFD compressor maybe??

  13. #13
    Join Date
    Jun 2010
    Location
    U.A. (upper Alabama)
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    872
    I don't know if I understand your question, but in my experience if you have a condenser pump with a vfd you use the D.P. (LIFT) on the refrigerant side to control the pump speed. You could use the D.P. on the cond. water side as long as your water does not get too cold. Are these chillers common piped on the condenser? BTW, the chiller is going to continue to make cold water as long you stay within the min. and max. temp. ranges for the entering condenser water, and have the proper flow.

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