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  1. #1

    Seconday and Primary pumps

    Hi guys, should secondary pumps flow be equal or greater than the primary flow, i mean, when choosing pumps for chilled water system, should i install secondary pumps that are greater in flow capacity than the primary pumps or both should be equal?

    Many thanks,

  2. #2
    Join Date
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    Pump should be selected based on the flow necessary for the circuit.
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  3. #3
    Quote Originally Posted by comfortdoc View Post
    Pump should be selected based on the flow necessary for the circuit.
    as i understand, the primary pumps are sized based on chillers water flow, but im not sure about secondary pumps, should secondary pumps be equal to primary pumps flow or to the flow demand of the cooling units they serve for (AHU, fan coil unit ...)

  4. #4
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    Quote Originally Posted by rami_9630 View Post
    as i understand, the primary pumps are sized based on chillers water flow, but im not sure about secondary pumps, should secondary pumps be equal to primary pumps flow or to the flow demand of the cooling units they serve for (AHU, fan coil unit ...)
    they are almost never equal, the primary pump is sized to move fluid throughout the heat exchanger, the secondary pump is sized to move fluid throughout the loads.
    just figure the pump head needed by each circuit.

  5. #5
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    This thread should be in one of the "Chillers" section. Ask a moderator to move it. Try clicking on the "!" in the lower left corner of your post. I'm thinking the secondary pump(s) should be sized based on the load (and lift?), and the primary pump(s) should be sized based on their respective chiller(s). But I'm not certain. Maybe I'm wrong about moving this thread. Is it a residential application? I was not aware primary/secondary loops were used there.

  6. #6
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    Moved to Tech to Tech.
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  7. #7
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    Primary pump= flow of the device doing the work.

    Secondary pump= sized for the load.

    Think of it this way, there can be numerous primary and/or secondary pumps..... This should clarify the thought process...

    I have a building with two primary pumps (one for each chiller) and two secondary pumps (building split into two phases) but only one water system.

    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  8. #8
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    This may help
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  9. #9
    Quote Originally Posted by alcomech View Post
    This may help
    thanks for the pdf, very informative.

  10. #10
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    You are welcome. It was posted by someone else.

  11. #11
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    You would always want primary flow to be larger than secondary flow. You can violate that for short periods but doing so for any degree of time will cause lots of problems with humidity and such.

  12. #12
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    Quote Originally Posted by Russ57 View Post
    You would always want primary flow to be larger than secondary flow. You can violate that for short periods but doing so for any degree of time will cause lots of problems with humidity and such.
    This is not 100% accurate...

    All depends on the temperatures and approaches of the chilled (or hot water) medium and overall controls scheme.

    The secondary loop flows can exceed the primary loop flows indefinitely. In fact, they do most of the time.
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  13. #13
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    Quote Originally Posted by rami_9630 View Post
    Hi guys, should secondary pumps flow be equal or greater than the primary flow, i mean, when choosing pumps for chilled water system, should i install secondary pumps that are greater in flow capacity than the primary pumps or both should be equal?

    Many thanks,
    Based on your question, you need an engineer. If you're planning on choosing pumps based on information given over an open internet forum and not on your own proven ability to do so and do so correctly, you're openin' a can of worms that may be very hard to close.

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