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  1. #1
    Join Date
    May 2002
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    Baton Rouge, Louisiana
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    3,879

    Chiller Plant Sequencing

    I'm doing a chiller plant with 3 chillers and 2 chillers have isolation valves. My question is this, how do you go about sequencing your chillers such as resettting temps and when, when lead chiller fails how do you prove it, temp vs. time? How long do you wait after opening valves to start the other chillers?

    I've done all this before but here in La, when the temps and humidity creep up 5 minutes could mean you dont catch up for the day, on the other hand properly protecting equipment so a chiller isn't cutting off and on every 5 minutes is paramount. Just trying to get a general concensus on how to make my sequencing more efficient.
    Quote Originally Posted by MatrixTransform View Post
    very soon it is you that will be pwned

  2. #2
    Join Date
    Jul 2008
    Posts
    1,461
    Chiller Isolating?

    Ive seen valves on condenser water for some screw chillers that need to get the pressure up quickly to move oil...but never really seen isolating on chw.

    Youre controlling leaving water right? if LVG-T isnt down to setpoint, then start another chiller. wait-open valves-wait-start pump-wait-start chiller.

    I suggest staging chillers off based on RET-T (inside the bypass/balance loop) as the bypass opens, the return water temp starts to drop (or flow in the bypass/balance line increases) or when the flow equals one CHW Pump worth, then you dont need the chiller....shutdown. Stop chiller-Stop Pump-close valves.
    1 + 1 = 3 ( *** for very large values of 1)

    ...everybody wants a box of chocolates and long stemmed rose

  3. #3
    Join Date
    May 2002
    Location
    Baton Rouge, Louisiana
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    3,879
    This is a 30 year old campus we are doing some upgrades on. It has a constant flow pump in each building(2) for this plant. Isolation valves are installed in the 2 smaller chillers because water flows through all chiller barrels all the time, now we can cut flow to the chillers that are not needed. Matrix how long do you usually wait to make the call for another chiller 5 minutes or 30 minutes, I've seen it spec'd both ways for failure on startup and for regular staging.
    Quote Originally Posted by MatrixTransform View Post
    very soon it is you that will be pwned

  4. #4
    Join Date
    Dec 2010
    Location
    Down by the river
    Posts
    1,650
    most my chiller plants are on 10-15 min b-4 it brings on the next chiller.

  5. #5
    Join Date
    Jan 2008
    Location
    Near Philly
    Posts
    512
    Hey Joey,

    By the short description, I'll assume a "variable flow primary pump" meaning a single VFD pump does all. In this application chillers are normally isolated out when not online. Usually, with all multipliable chiller applications, the question that comes to the top is " when to add or subtract a chiller?" The answers are as many as there are licensed PE's in your state. Here is what look for in a good sequence. Two or more arguments must agree to start and two have to agree to stop. Example, common leaving temp setpoint is 45 deg, above 47 deg add another chiller? OK second chiller starts, temp now goes to 45 deg in 20 minutes, second chiller Off? Better, common leaving temp setpoint is 45 deg, above 47 deg and chiller1 KW is greater than 95%, start chiller 2. To remove a chiller, common temp needs to be lower than 45 deg and both chillers KW is less than 65%. The same principled can be applied with several different inputs, flow rates, valve positions, temp sensors, KW readings, all kinds of combinations. The " latch logic" I described can be deployed with most systems. If it is the system type I described, flow rates will usually have a major say-so in the sequence of operation.

  6. #6
    Join Date
    May 2002
    Location
    Baton Rouge, Louisiana
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    3,879
    Quote Originally Posted by mechdorn View Post
    Hey Joey,

    By the short description, I'll assume a "variable flow primary pump" meaning a single VFD pump does all. In this application chillers are normally isolated out when not online. Usually, with all multipliable chiller applications, the question that comes to the top is " when to add or subtract a chiller?" The answers are as many as there are licensed PE's in your state. Here is what look for in a good sequence. Two or more arguments must agree to start and two have to agree to stop. Example, common leaving temp setpoint is 45 deg, above 47 deg add another chiller? OK second chiller starts, temp now goes to 45 deg in 20 minutes, second chiller Off? Better, common leaving temp setpoint is 45 deg, above 47 deg and chiller1 KW is greater than 95%, start chiller 2. To remove a chiller, common temp needs to be lower than 45 deg and both chillers KW is less than 65%. The same principled can be applied with several different inputs, flow rates, valve positions, temp sensors, KW readings, all kinds of combinations. The " latch logic" I described can be deployed with most systems. If it is the system type I described, flow rates will usually have a major say-so in the sequence of operation.
    No variable flow pumps, this plant serves 2 buildings with a constant flow pump in each building. I am not taking KW readings and have used that approach before but with results I wasnt too happy with because one chiller was a giant piece of crap and the other one was new and up to the task so depending on which chiller was lead the other one would cycle on and off every 30 minutes
    Quote Originally Posted by MatrixTransform View Post
    very soon it is you that will be pwned

  7. #7
    Join Date
    Jan 2008
    Location
    Near Philly
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    512
    Quote Originally Posted by joey791 View Post
    No variable flow pumps, this plant serves 2 buildings with a constant flow pump in each building. I am not taking KW readings and have used that approach before but with results I wasnt too happy with because one chiller was a giant piece of crap and the other one was new and up to the task so depending on which chiller was lead the other one would cycle on and off every 30 minutes
    So the same flow is cut in halve when another chiller is brought on-line? The place where your working should consider some professorial engineering consultation. Run, joey run.

  8. #8
    Join Date
    Dec 2010
    Location
    Central US
    Posts
    415
    Sounds challenging! May I ask a few questions.
    1. What are the 3 chillers tonages and type? Centrifigul, screw etc.. water cooled or air cooled. and which chillers have the iso valves(need to know if the valves are 2 pos or modulating and where located chilled water or condenser side or both.
    2. Constant volume Pump in each building (I assume they run 24/7 or when buildings are occupied and at the same times)
    3. Are there any dedicated pumps for the chillers, or pumps that serve the chiller plant(What im getting at is primary/secondary system, series or parrallel and or decoupler/bypass)
    4. What temp sensors are in place and flow meters if any? (Is this a design build or existing system you are fixing)

    Need this info to start.

  9. #9
    Join Date
    Sep 2004
    Location
    Kansas City, Kansas, United States
    Posts
    13,832
    obviously, you can no run chilled water through any stopped chillers!!!!!!!!!!!!!!!!!!!!!!!

    I imagine you have these chillers piped in parallel and 3 separate chw pumps????????

    I have many accounts with 3 chillers.

    44 degree leaving water, 45 degrees for 15 minutes and chiller 2 comes on 46 degrees for 15 minutes and chiller 3 comes on.

    I havd ddc controls closing or isolating the chw on chillers not calling!

    ofcourse lead lag all 3 chillers.

    Mostly what I have is centravacs, but I also have a few 19d and YK!!

    The carrier chillers do their own lead lag and the YK I lead lag them every start!

    just going on bla bla bla!!

    Frank
    I WILL SELL WORK,GENERATE BUSINESS, GO GET NEW CUSTOMERS!
    YOU SHUT THE HELL UP AND QUIT RUNNING YOUR MOUTH!

  10. #10
    Join Date
    Nov 2005
    Location
    Shreveport, Louisiana
    Posts
    2,329
    Quote Originally Posted by joey791 View Post
    I'm doing a chiller plant with 3 chillers and 2 chillers have isolation valves. My question is this, how do you go about sequencing your chillers such as resettting temps and when, when lead chiller fails how do you prove it, temp vs. time? How long do you wait after opening valves to start the other chillers?

    I've done all this before but here in La, when the temps and humidity creep up 5 minutes could mean you dont catch up for the day, on the other hand properly protecting equipment so a chiller isn't cutting off and on every 5 minutes is paramount. Just trying to get a general concensus on how to make my sequencing more efficient.


    Can you make inputs to a controller from each chiller for chiller status and alarm points from the individual chillers. Are the chillers equal tonnage? Do you have ways to load and unload chillers say water setpoints or current limits setpoint control?
    UA Local 141

  11. #11
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    Feb 2005
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  12. #12
    Join Date
    May 2002
    Location
    Baton Rouge, Louisiana
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    3,879
    Quote Originally Posted by emcontrols View Post
    Sounds challenging! May I ask a few questions.
    1. What are the 3 chillers tonages and type? Centrifigul, screw etc.. water cooled or air cooled. and which chillers have the iso valves(need to know if the valves are 2 pos or modulating and where located chilled water or condenser side or both.
    2. Constant volume Pump in each building (I assume they run 24/7 or when buildings are occupied and at the same times)
    3. Are there any dedicated pumps for the chillers, or pumps that serve the chiller plant(What im getting at is primary/secondary system, series or parrallel and or decoupler/bypass)
    4. What temp sensors are in place and flow meters if any? (Is this a design build or existing system you are fixing)

    Need this info to start.
    1. I do not have tonnages right now. 2 Trane air cooled screw chillers and 1 Carrier scroll chiller air cooled. 1 Trane chiller is about a year old and will be lead, 1 RTAA104 has an iso valve on the chill water on/off, Carrier has an iso valve on the chill water on/off.
    2. Constant volume pump in each building seem to run at the same time, I haven't seen one drop yet and the other run, both run on occupancy.
    3. No dedicated pumps for chiller just these 2 loop pumps, 1 in each building.
    4. Chill water supply out of each chiller and common return for both buildings. No flow meters, there never were any. One building is 30 years old the other is 40 years old. The original plant had 4 chillers but since all chillers have been changed over the past 5 years has been widdled down to 3. Controls were originally JCI pnuematics then start/stop control was changed to Robertshaw controls, now I'm pulling the Robertshaw controls out and putting our stuff in.
    Quote Originally Posted by MatrixTransform View Post
    very soon it is you that will be pwned

  13. #13
    Join Date
    May 2002
    Location
    Baton Rouge, Louisiana
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    3,879
    Quote Originally Posted by berg2666 View Post
    Can you make inputs to a controller from each chiller for chiller status and alarm points from the individual chillers. Are the chillers equal tonnage? Do you have ways to load and unload chillers say water setpoints or current limits setpoint control?
    Wire has been pulled and alarm points were not included. Chillers are not equal tonnage(at least the Carrier is a smaller tonnage for sure). We have wire ran for chill water reset on all chillers, Trane came with it, the Carrier does not have an EMM module to reset chill water with.
    Quote Originally Posted by MatrixTransform View Post
    very soon it is you that will be pwned

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