Kloves YK Surging help!
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  1. #1
    Join Date
    Sep 2008
    Location
    Texas
    Posts
    371

    Kloves YK Surging help!

    Klove, some time ago you helped me with a yk surging. We talked about the loop bypass being in the wrong place. Well, I finally shut the plant down the other night and welded in a valve in the bypass. May be hard to get the full picture but the 4 chillers have dedicated pumps to each. I was able to use the 150ft hd vsd "loop pumps" to pump through the dead chiller pumps, through the chiller and out to the loop with no option of bypass. It now can be ran as a vairable primary once we get some contol issues out of the way. We were running 1250 tons with 1000gpm less pumping that one day before this with a constant discharge water temp. The loop pumps need tweeking and that is were my question comes in. What is the max rate of change that York wants to see with chill water flow? What about return water temp rate of change? There is about 10 buildings on the loop that will demand flow as required.

    Thanks! Others invited to join in as well!!
    "Dying aint much, its living thats hard." (Josey Whales)

  2. #2
    Join Date
    Dec 2008
    Location
    Dixiana, AL
    Posts
    2,609
    I'm sure there may be an engineering solution to the rate of change question on both variables that you mentioned, and I do have (somewhere) an ancient York form on variable flow primary that may have a number in it. If so, I'll get it to you. Pretty much the way we always looked at it was to stay as far away from VP as we could because of the control issues that it entails - pump drives fighting chiller capacity control systems fighting pump drives just don't make for a good day.

    That said, here's what I did when not given a choice. Get the control folks to add enough slop in their system to slow down the response rate to "barely acceptable" on the pump speed changes. Then add as much slop as you can get in the chiller response to change. If you're using Optiview, go to the evaporator screen in service mode and set the sensitivity to 30% if you have that software. Keep your pump speed and process (or cooling) controls at a point where you will not go below minimum flow on the cooler. This may not leave a choice but to have a controlled bypass. I try to stay inside the minimum flow point as much as possible, don't even like to look at the low end. Especially if you have VSD's on the chillers, you'll need an interminably slow response time to keep out of surge. I believe you'd rather lose a little temp on the loop periodically than have the chillers operating all over the map. Plus, from your description, it sounds as if you have a large loop with probably alot of flywheel effect, so short term minor loss of loop temp/flow during unstable periods aren't going to be too detrimental to your operation, and unless they're throwing whole buildings on/off line I would think that once the loop is stable, it has a tendency to remain that way.

    Out of curiosity, why not just fix the primary pumps and run the system as advertised? (Under the conditions you have, I think I'd gut the primaries if I had to pump thru them.) Again, I'll try and find the VPFlow engineering guide and see if it has any specific info that might be helpful to you. May take a day or three, but I'll be in touch.

  3. #3
    Join Date
    Sep 2008
    Location
    Texas
    Posts
    371
    Thanks clove! The original piping looks like this. The vsd loop pumps (150 ft hd) pump from the loop into a header lets call it the loop header. This header splits off into the suctions of each chiller pump. Each chiller has a pump with chiller deign GPM but the ft hd on #4 is 20 and on #2 is 55 so as you know when we start #1 and 3 together #4 looses flow. Mismatched chiller pumps problem #1! #2 problem is four different delta t chillers. Problem #4 the pressure drop across each chiller is different. The reason that is a problem will make sinse after I explain this: The water leaves each chiller and can take a left to exit the plant or take a right to enter the loop header again. This is the bypass I spoke of. Chiller #2 is a YK with VSD. The bypass can flow + or -. When it flows minus it dumps supply water into chiller #2 return causing it to surge until it can correct its self. In the winter it will shut down on extended surge. They have only been able to run this VSD York in the summer. What a waste! So hears the deal, we spent $1000 bucks welding in a valve. I shut the bypass. I killed all chiller pumps at their disconnect and started the plant with two chillers. First thing I noticed was we reduced the total water volume being moved by 1000 gpm. This was a cheap way of trying variable flow without commitment. I dont know if you are an old school constant flow guy but I once was and stated that "variable primary will not work" only to be proven wrong. I like the idea for this facility. They installed a flow meter in the loop supply and say they have never seen the flow drop below 1000 GPM in the winter. Chiller #2 is a 3500 gpm chiller. I do need to find the the min flow however. We talked about setting up Tracer to start and stop chillers based on total flow required. I can invision a problem when we start a second chiller by just opening the isolation valve thus reducing the flow suddenly in the loaded chiller thats running. Trying to think through the potential problems ahead of time. I hope that we can control flow enough to utilize the York most of the time. One other issue I can think of is when they start and stop some of the buildings on time schedules the flow will be affected suddenly. This is a university where the dorms stay on but allot of buildings shut off. Each building has a pump.
    "Dying aint much, its living thats hard." (Josey Whales)

  4. #4
    Join Date
    Dec 2008
    Location
    Dixiana, AL
    Posts
    2,609
    Hey Cap'n,

    Tonites prayer meetin' so I can't spend a lot of time responding at the moment, but I did want to run a beginning solution past you based on your description of the situation. I think I'd take a vote to see who gets to shoot whoever did the eqpt selection in the chiller plant! What a nightmare!

    And yes, I am "old school" where most things are concerned, but not so much that I won't try and work with what's there with an open mind. I just have a real hard time when folks throw the KISS principle out the window. I'll be in touch as soon as I come up with that engineering form.

  5. #5
    Join Date
    Jul 2006
    Location
    The Great country of Texas
    Posts
    429
    Quote Originally Posted by CaptJackSparrow View Post
    Thanks clove! The original piping looks like this. The vsd loop pumps (150 ft hd) pump from the loop into a header lets call it the loop header. This header splits off into the suctions of each chiller pump. Each chiller has a pump with chiller deign GPM but the ft hd on #4 is 20 and on #2 is 55 so as you know when we start #1 and 3 together #4 looses flow. Mismatched chiller pumps problem #1! #2 problem is four different delta t chillers. Problem #4 the pressure drop across each chiller is different. The reason that is a problem will make sinse after I explain this: The water leaves each chiller and can take a left to exit the plant or take a right to enter the loop header again. This is the bypass I spoke of. Chiller #2 is a YK with VSD. The bypass can flow + or -. When it flows minus it dumps supply water into chiller #2 return causing it to surge until it can correct its self. In the winter it will shut down on extended surge. They have only been able to run this VSD York in the summer. What a waste! So hears the deal, we spent $1000 bucks welding in a valve. I shut the bypass. I killed all chiller pumps at their disconnect and started the plant with two chillers. First thing I noticed was we reduced the total water volume being moved by 1000 gpm. This was a cheap way of trying variable flow without commitment. I dont know if you are an old school constant flow guy but I once was and stated that "variable primary will not work" only to be proven wrong. I like the idea for this facility. They installed a flow meter in the loop supply and say they have never seen the flow drop below 1000 GPM in the winter. Chiller #2 is a 3500 gpm chiller. I do need to find the the min flow however. We talked about setting up Tracer to start and stop chillers based on total flow required. I can invision a problem when we start a second chiller by just opening the isolation valve thus reducing the flow suddenly in the loaded chiller thats running. Trying to think through the potential problems ahead of time. I hope that we can control flow enough to utilize the York most of the time. One other issue I can think of is when they start and stop some of the buildings on time schedules the flow will be affected suddenly. This is a university where the dorms stay on but allot of buildings shut off. Each building has a pump.
    Calvin said he can fix with a P.O.! LOL Is this at AC?
    "I'm from Texas, what country are you from?"

  6. #6
    Join Date
    Sep 2008
    Location
    Texas
    Posts
    371
    Stickerhead
    Yep! I think it will work if the flow rate of change is slow enough. I ran it for a day like this and all was good but a light load one chiller operation will tell the story. I hope to be able to utlize the YK. Klove talked about adusting the expansion valve contol in an earlier post so I have to get my YK book out. I haer you are going to Houston? Oopps you may not have known yet!!!
    "Dying aint much, its living thats hard." (Josey Whales)

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