Say What
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Thread: Say What

  1. #1
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    Say What

    I have just completed annuals on 2 Identical Carrier 19EA8167DL machines. They both have the same model numbers and the serial numbers are in sequencial order. The gear ratios are the same, unishells are the same, locked rotor amperage is the same 4330 amps delta, 1443 wye. The motors are the same, the DL= a 692 kw motor. The #1 chiller is rated at 949 amps RLA @460 volts while chiller #2 is rated at 869 amps at 460 volt. The overloads have been calibrated to the lower value as that is what the starter name plate spec's out. The chillers are single pass evaporators and in series. How can ch-1 have a higher RLA then ch-2 with all things being equal-GEO

  2. #2
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    So chiller #1 takes the brunt of the load first right ?Is there something special about the piping set-up?
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  3. #3
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    Check into the # and size/style of tubes in the machines . Thats probably where the difference is . first chiller in line does example 60/48 second does 48/42 LWT ??
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  4. #4
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    Because the downsteam chiller has a higher differential pressure to work against than the upsteam chiller.
    Tight is tight, Too tight is broke.

  5. #5
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    I've got a site with very similar setup on 2 York YK's, except the 2nd chiller has a motor current rating 10% higher than the upstream machine. I figured it was due to lift requirement of 2nd chiller but that doesn't seem to work in your example. I'm interested to see what everyone says on this topic.

  6. #6
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    2 of the same, only different !

    1) Piping sized the same, Delta P's are the same, Delta T's are 7*F per chiller. Chiller 1 56*F- 49*F, Chiller 2 49*F- 42*F. 340 tubes in each evaporator (single pass) and 475 in each condenser (2 pass). Each of the overloads are calibrated at the 869 amp setting. The original start-up sheets (submittals) are a carbon copy of one another except for RLA. Why is there is 63kw of difference for the same motor.-GEO

  7. #7
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    Quote Originally Posted by ga1279 View Post
    1) Piping sized the same, Delta P's are the same, Delta T's are 7*F per chiller. Chiller 1 56*F- 49*F, Chiller 2 49*F- 42*F. 340 tubes in each evaporator (single pass) and 475 in each condenser (2 pass). Each of the overloads are calibrated at the 869 amp setting. The original start-up sheets (submittals) are a carbon copy of one another except for RLA. Why is there is 63kw of difference for the same motor.-GEO
    someone made an error on paper at the factory........

  8. #8
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    I would assume it is related to the density of the gas in the down stream machine.
    Along with higher diff. ref. pres. as stated before.

    Much like you see when you put a machine into ice building mode.
    You can open the vanes all the way up and not load the motor.

    Try puttig the 56 degree water on this machine and see what happens.

  9. #9
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    Quote Originally Posted by ga1279 View Post
    1) Piping sized the same, Delta P's are the same, Delta T's are 7*F per chiller. Chiller 1 56*F- 49*F, Chiller 2 49*F- 42*F. 340 tubes in each evaporator (single pass) and 475 in each condenser (2 pass). Each of the overloads are calibrated at the 869 amp setting. The original start-up sheets (submittals) are a carbon copy of one another except for RLA. Why is there is 63kw of difference for the same motor.-GEO
    Because chillers aren't rated at actual horsepower but at nominal horsepower to do XXX amount of work. A 500 TR chiller may have a 461 HP motor, but that's based on nominal, not actual. Actual, in that case, is probably 500 HP, 'cause they don't make a 461 HP motor. The KW, like the HP, is figured nominally for the amount of power needed to perform the rated work, thus the disparity. Given the same cooling tower water at the same amounts into both condensers so that condenser pressure is the same, normally the downstream machine in a series configuration will require the most power at nominal TR to make the load, because of increased lift, as has already been stated. You could check with the factory and make certain that the motors are the same, and then set them up as called for except for reversing the serial numbers.

    My guess would be that since the machines were identical, the poor ol' pipefitter superintendent didn't know to look any farther and reversed the chillers at installation, and the startup mechanic recalibrated to fit when he discovered the problem. I would think that if this is the case, it was probably brought to the attention of all involved, and the decision was made to try things that way before they went to the trouble of swapping the machines. Since it's so close on power nominally (and they should have been - they're identical), it worked, and noone was any the wiser. You're probably the first one that's ever questioned the discrepancy.

  10. #10
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    The lift is the key. Since lift is the function of saturation differences, the colder machine requires more lift, therefore will require more HP. Since they tend not to undersize the motor, the warm machine does not require as much HP hince lower RLA
    "I'm from Texas, what country are you from?"

  11. #11
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    Quote Originally Posted by heavymetaldad View Post
    someone made an error on paper at the factory........
    Finally saw 'in series'.




    Darn sunlight got in my eyes.

  12. #12
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    Quote Originally Posted by heavymetaldad View Post
    Finally saw 'in series'.




    Darn sunlight got in my eyes.
    Generally, it's just my brain that gets in the way..............

  13. #13
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    Many Thanks

    I believe I have received an answer and it is not what has been stated previously in this thread. While I do agree with the question of lead/ lag swap during installation, then of course the differences in lift. It has more to do with motor design. Way back in the last century (circa 1974) when the EA and EB were in major design applications in the state of TEXAS, the engineers at Carrier went with a Random wound motor only to have most of their install crater within the first 12 months. This larger motor is one that actually made it through. What I didn't realize is there is one major difference the motor length. The random wound motor is shorter and uses a spacer above the unishell and the replacement motor runs all the way back to the condenser tube sheet. As I understand it there were about a dozen of these at least that were installed in the Dallas area, but didn't make it through the first year. Again many thanks to all and look forward to talking to yaw'll again-GEO

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