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Thread: Fluid Dynamics

  1. #1
    Join Date
    Jul 2010
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    Denver, CO
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    Fluid Dynamics

    I just took over an older apartment building and have been going through all the systems and equipment.
    When I got to the chiller, I found a 60ton Multistack with a 500gpm evaporator pump at 11ft/hd and a condenser pump at 442gpm at 80ft/hd, this raised a flag so I contacted Multistack. This chiller is designed for 190gpm at 6.5psi on the evaporator and 230gpm at 9psi.
    Needless to say I can not get the system to run down to 45 degrees nor get the proper temperature rise on the condenser.
    I am curious from those who understand more about fluid and thermo dynamics, what problems/issues are happening due to this lack of engineering. I know that the water is moving to fast to achieve the proper heat transfer, but is there more beyond that?

    One other question, when pumps are piped in series, is the GPM added and the head whichever is larger?

  2. #2
    Join Date
    Jul 2007
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    You can also erode the tubes if the flow is above max flow. Can you valve back the pumps?

  3. #3
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    do you have pumps in series? is that how you are getting your flow rates?

    valving back the pumps may be ok but you better look at a flow diagram...i saw several B&G pumps that could do 442 gpm at 80 feet but you couldn't back them down much...if you did you would be in the 'rumble' zone and that wouldn't be good. the evaporator side wasn't much better. you are going to need to be looking at new pumps.
    When the rich wage war, it's the poor who die - Linken Park

  4. #4
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    I will be looking at a replacement chiller. The pumps are original to the building, piped in series. After some rough calculations I figured the building has about a 210 ton heat load, 200 tons is right around 500 gpm. The chiller is undersized, the pumps are correct. Imagine that.
    I am just curious for curiosity sake what issues this is causing besides the obvious.

  5. #5
    Join Date
    Jul 2011
    Location
    East coast USA
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    975
    You need a balance report. I have a similar issue. I know what i have in equipment,what i don't have is actual flow rates. So i plan on getting some test done. I have the original balance reports..amazing i found them and use this as a bench mark. If your planning on changing the system your gong to need this anyway.

  6. #6
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
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    Quote Originally Posted by HuNGRYTeCH View Post
    I will be looking at a replacement chiller. The pumps are original to the building, piped in series. After some rough calculations I figured the building has about a 210 ton heat load, 200 tons is right around 500 gpm. The chiller is undersized, the pumps are correct. Imagine that.
    I am just curious for curiosity sake what issues this is causing besides the obvious.
    pumps that are correct for basic flow rates does not mean that they are correctly piped.
    When the rich wage war, it's the poor who die - Linken Park

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