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  1. #1
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    Chilled Water System with a return loop in a tall building

    I have just seen an old (1980) Chiller Water System Design with the attached layout.

    Does anybody know why would the return system be designed as shown in the picture?
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  2. #2
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    One thing that I see Is the fan coil closest to the supply is the last on the return. It make sense to "balance" the flow at each coil

    Why have they went so high with the return I don't know.

  3. #3
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    Quote Originally Posted by patpinet View Post
    One thing that I see Is the fan coil closest to the supply is the last on the return. It make sense to "balance" the flow at each coil

    Why have they went so high with the return I don't know.
    Closed System or Open?

  4. #4
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    I have alway know it as a reverse return system. If the pipe sizing is done right it will tend to self balance.
    They may have gone high on the return to help get the air out, high point of the loop.
    May not be done a lot any more due to cost , it takes a extra pipe.


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  5. #5
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    Quote Originally Posted by pecmsg View Post
    Closed System or Open?
    Closed system, i still pipe this way even if you have two fan coils, water heaters, air handlers it doesn't matter length of pipe still get equal flow. Can use circuit setters but setting them up takes time, down the road someone changes a setting on one cs the whole system is changed. And theres probably a dozen different ways to pipe a system they all work just some better than others it all depends how the engineer design a system.

  6. #6
    Join Date
    Nov 2001
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    Quote Originally Posted by Chev5372 View Post
    I have alway know it as a reverse return system. If the pipe sizing is done right it will tend to self balance.
    They may have gone high on the return to help get the air out, high point of the loop.
    May not be done a lot any more due to cost , it takes a extra pipe.
    Yep, that is a reverse return system. The idea is that the difference in pressure between the supply and return will be the same on all floors. With the growth of variable speed pumping and pressure-independent valves I haven't seen these on recent designs, but I worked on a very large new hotel/resort complex back in 2012 that had it.

    If you're interested in learning more about the various options for piping tall buildings, the article by Steve Taylor of Taylor Engineering still holds up well even though it was written 17 years ago:

    http://www.taylor-engineering.com/We...ic_Systems.pdf

  7. #7
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    Chevy and coolcoil are right on target. It is a reverse return and is self balancing if properly sized.
    No man can be both ignorant and free.
    Thomas Jefferson

  8. #8
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    The attached page defines as to the direct and reverse return chilled water piping
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  9. #9
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    Reverse Return "Self Balances " in a way

  10. #10
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    Nov 2001
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    Quote Originally Posted by patpinet View Post
    Why have they went so high with the return I don't know.
    This is required in a reverse-return system so that the difference in the water column height of the supply and return risers is the same on each floor.

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