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  1. #53
    Join Date
    Aug 2009
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    Prattville, Alabama
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    2,145
    First, I'm all about solid reliability above all else. The more simple, the more reliable. Yet, I would be OK with operating and maintaining a plant like what is being speculated about, if it's designed and installed from the ground up. However, I'm not a typical plant operator. I would be concerned for a typical plant operator that is going through the process of making such modifications on an operating(?) plant, while trying to maintain conditions. Can the OP's facility survive scheduled downtimes? How about unscheduled downtimes? How about after the modifications are completed and all contractors are off site, and the operator is all alone? It will happen. If the OP's higher ups decide to go this route, I hope he is up to the challenge.

  2. #54
    Join Date
    May 2010
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    1,295
    We are prepared to run everything at 60Hz, because even though we are only "operating engineers", we know what the effects of this new VFD Chiller and pumps is going to have on us. We are screaming at the higher ups and the actual Engineers designing the setup that it isn't going to work.

    We know that the setup they are proposing isn't going to work and cause a hell of a situation for us. I brought forth my opinion to the engineers when they last came and you could tell a light bulb went off in their head that their proposed setup isnt going to work!!!!

  3. #55
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
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    2,145
    I hope things work out for the best for you. Good luck with trying to figure out what's going on in the head of an engineer.

  4. #56
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
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    1,787
    Quote Originally Posted by ZeroTolerance View Post
    We are prepared to run everything at 60Hz, because even though we are only "operating engineers", we know what the effects of this new VFD Chiller and pumps is going to have on us. We are screaming at the higher ups and the actual Engineers designing the setup that it isn't going to work.

    We know that the setup they are proposing isn't going to work and cause a hell of a situation for us. I brought forth my opinion to the engineers when they last came and you could tell a light bulb went off in their head that their proposed setup isnt going to work!!!!
    Like I said earlier, it will still 'work' just fine, it just won't be able to provide the full efficiency advantage of the compressor VFD without being able to lower condenser temps. I'm betting the variable compressor will still have much better part-load efficiency than the non-vfd chillers, so as long as the controls sequence it to utilize the old chillers at near full load (where THEY are likely more efficient), and the new chiller at part load to control overall supply temp, you'll still likely be more efficient than a completely non-vfd system. Whether it will pay for the vfd upgrade, I'm not sure.

    Another thing to consider is, how much life is left in the other chillers in the loop? Will they be replaced within the next 10 years or so? If so, if you DON'T go with VFD on the new one now, you'll be asking these same questions when the others are replaced down the road. Then, if you DID have 2 or more of your chillers variable, you can likely run through the shoulder seasons with the lower condenser temp just fine.

  5. #57
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
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    3,725
    Quote Originally Posted by CraziFuzzy View Post
    Like I said earlier, it will still 'work' just fine, it just won't be able to provide the full efficiency advantage of the compressor VFD without being able to lower condenser temps. I'm betting the variable compressor will still have much better part-load efficiency than the non-vfd chillers, so as long as the controls sequence it to utilize the old chillers at near full load (where THEY are likely more efficient), and the new chiller at part load to control overall supply temp, you'll still likely be more efficient than a completely non-vfd system. Whether it will pay for the vfd upgrade, I'm not sure.

    Another thing to consider is, how much life is left in the other chillers in the loop? Will they be replaced within the next 10 years or so? If so, if you DON'T go with VFD on the new one now, you'll be asking these same questions when the others are replaced down the road. Then, if you DID have 2 or more of your chillers variable, you can likely run through the shoulder seasons with the lower condenser temp just fine.
    I have a feeling it will not be running at part load with warm condenser water, it just might surge.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  6. #58
    Join Date
    May 2010
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    1,295
    Our other chillers were put in in August of 2007, so they are fairly new. They are both CVHE 600-tons running ucp4

  7. #59
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
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    Quote Originally Posted by Dallas Duster View Post
    I have a feeling it will not be running at part load with warm condenser water, it just might surge.
    Well, the way they control the compressor speed in most cases is to run just above the point of surging. Keep in mind, we're not talking about 'warm' condenser water, just not 'cold' condenser water. It shouldn't be any closer to surging than a constant speed compressor - and and part load, it should have no problem backing off speed a bit, improving part load efficiency.

    Still, if the other chillers are that new, and not likely to be replaced, then the other part of my argument is invalid - unless of course they are new enough to receive VFD upgrades in the next few years.

    This conversation DOES make me glad our plant has 2 separate towers. We've got 2 1985 vintage CVHE-750's on one tower, and 3 1990 vintage CVHE-1250's on the other. We are in the planning stages of replacing the 750's with some newer 750's, but since they are on a separate tower and can run colder, the VFD's are a no-brainer.

    One recommendation I have is, if they DO end up putting in the VFD chiller, perhaps it might be worth it to see what it would take to add a 3-way, or a pump return bypass, on one or two of the constant speed chillers. You might be surprised how little it would cost, and the gains would be huge.

  8. #60
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    Aug 2009
    Location
    Jurupa Valley, CA
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    Since you already have dedicated pumps for each chiller (I think you said that), getting variable temp condenser water to each chiller may only require cutting in a simple modulating valve across each pump take-off like so:

    This way, the pump is just concerned with the right GPM through the chiller, and the bypass valve will vary to regulate the temperature of the water into the chiller.

  9. #61
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
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    Quote Originally Posted by CraziFuzzy View Post
    Well, the way they control the compressor speed in most cases is to run just above the point of surging. Keep in mind, we're not talking about 'warm' condenser water, just not 'cold' condenser water. It shouldn't be any closer to surging than a constant speed compressor - and and part load, it should have no problem backing off speed a bit, improving part load efficiency.

    Still, if the other chillers are that new, and not likely to be replaced, then the other part of my argument is invalid - unless of course they are new enough to receive VFD upgrades in the next few years.

    This conversation DOES make me glad our plant has 2 separate towers. We've got 2 1985 vintage CVHE-750's on one tower, and 3 1990 vintage CVHE-1250's on the other. We are in the planning stages of replacing the 750's with some newer 750's, but since they are on a separate tower and can run colder, the VFD's are a no-brainer.

    One recommendation I have is, if they DO end up putting in the VFD chiller, perhaps it might be worth it to see what it would take to add a 3-way, or a pump return bypass, on one or two of the constant speed chillers. You might be surprised how little it would cost, and the gains would be huge.
    So most likely it will be running balls to the wall all the time.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  10. #62
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    Aug 2009
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    Jurupa Valley, CA
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    Quote Originally Posted by Dallas Duster View Post
    So most likely it will be running balls to the wall all the time.
    That would depend on the other chillers setpoints.

  11. #63
    Join Date
    Oct 2011
    Location
    South Georgia
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    73

    Hmm

    My opinion ( for what it is worth) is that all of these mechanical design engineers need to start paying for their mistakes and experiments. They have become just like doctors, they cover for each other and admit no mistakes. Seems like every start up i go into has the same old stupid mistakes. You would think that by now they should now what to do with head pressure controls. Maybe it's my impatience, but i get tired of the same old arguments. I have however seen a few good enginnered projects, but they are getting less frequent.

    My statement does not ascertain that service engineers and building engineers are smarter than desigb, but sometimes i think they need to listen to the voice of experience.

    In your case it would seem that a serious discussion needs to occur. Reading these posts indicates the answers are available, it simply is a matter of everybody getting on the same page and planning well ahead of time, especially the controls.

  12. #64
    Join Date
    Jul 2007
    Location
    The Hot South
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    1,372
    Quote Originally Posted by ZeroTolerance View Post
    Our other chillers were put in in August of 2007, so they are fairly new. They are both CVHE 600-tons running ucp4
    Then they have the refrigerant pumps and can take the lower condenser temps.

  13. #65
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    4,530
    Quote Originally Posted by CraziFuzzy View Post
    ...This conversation DOES make me glad our plant has 2 separate towers. We've got 2 1985 vintage CVHE-750's on one tower, and 3 1990 vintage CVHE-1250's on the other. We are in the planning stages of replacing the 750's with some newer 750's, but since they are on a separate tower and can run colder, the VFD's are a no-brainer.....
    i would agree with you here. earlier, i was thinking of 3 way valves on the towers instead of on the individual condenser pumps...working in the heat had gotten to me. that i also like and it may work if the controls are set up properly and left alone. it does add for individuallity of the condenser water temperatures per chiller. i have had trane chillers that lost all of their oil with entering condenser water temperatures below 84F and i have had trane chillers that never lost a drop at 65F. individual control allows for age differences and mechanical issues. i would be concerned about being able to write a proper sequence and maintaining it. i don't have that kind of faith in the industry.

    it used to be that the experienced mechanical techs moved into the BAS field...now it is mostly young punks who grew up playing video games and don't know what dirt under a fingernail feels like.
    "If you pull one more stunt like you just pulled with Tommy, you won't have to get on a plane because I will personally kick your ass from here to Korea!" - Best of the Best

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