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  1. #1
    Join Date
    Apr 2005
    Posts
    517

    derating chillers

    Does anyone have any really good information on "engineering" heat transfer with glycol and derating the tonnage and/or btu's. Just looking for facts that could help every day kind of stuff. I am also looking for information that supports the percentage loss between propylene and ethylene glycols.

    Also looking for engineering studies about derating tonnage of chillers when leaving water temps setpoints drop from standard 40 F and below. I was just told by an engineer that with every degree setpoint drop in lvn water setpoint below 40 F equals around a 3% derate in tonage.

  2. #2
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,388
    from a trane catalog that i occasionally use.

    i also have a great article on the whole idea but it is from ASHRAE and it states right at the top to not distribute...sorry.

    good luck.
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  3. #3
    Join Date
    May 2008
    Location
    Jax Fl.
    Posts
    1,943
    Just as a reminder, Glycol of either type impacts the specific heat [capacity] and the viscosity [pump sizing].
    Make sure it is bio and corrosion inhibited or it can cause big problems.

  4. #4
    Join Date
    Jul 2008
    Location
    Washington, DC
    Posts
    1,583
    One thing that can go overlooked if you are retrofitting a system from water to glycol is the interaction between water treatment and glycol. It can be especially nasty on condenser water systems, open loop tower converted to closed loop drycooler. I'm not sure if your doing a retrofit or not, just throwing this out there.

    Derating will depend on the percentage of glycol in the mixture, so there is no single number. On a drycooler when you need to keep freeze protection down to say 0 there is a much bigger derating factor than if you are trying to run a chiller with 28 degree chilled fluid.

  5. #5
    Join Date
    Feb 2004
    Location
    New Mexico
    Posts
    5,540
    Looks like you got what you need.
    I can tell you that the losses can be huge. One example was a injecting moulding machine that needed 22 deg coolant. By the time the glycol mix was considered and the low temp the 17 ton chiller dropped to 5.5 tons.
    Tracers work both ways.

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