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Identical Pumps in Series vs. Parallel - flow rates vs. power consumption vs. longevity

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tivo
tivo Member Posts: 16
edited January 2017 in Thermostats and Controls
Two identical pumps piped in series vs. parallel:

Q1: Will either piping yield double the system flow rates?
Q2: Will the power consumption be equal in both cases?
Q3: Will either piping affect the life expectancy of the pumps? Just thinking the pumps piped in parallel might be working "harder" overcoming higher head vs. pumps in series sharing the resistance. But then, when the head/resistance is shared, the pumps in series work at a higher flow rates, i.e. potentially more wear and tear so to speak... so I can't draw a conclusion... as you can already tell, I'm no engineer.

Thanks in advance.

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  • Jamie Hall
    Jamie Hall Member Posts: 23,286
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    Q1. No. Parallel will almost double, but not quite -- how much off will depend on the system and pump head vs. flow curves. Series will also increase flow, but not double -- again, depending on the system and pump head vs. flow curves.
    Q2. In general, no. Depends on the efficiency characteristics of the pumps. However, it may be less power -- or it might be more.
    Q3. In most cases, no. In the rare situation that the increased flow causes a sufficiently low NPSH at the pump intake, you might, just possibly, cavitate, which will reduce the life expectancy considerably. Depends on the intake conditions.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • tivo
    tivo Member Posts: 16
    edited January 2017
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    Hi Jamie, thanks for your quick response. Could you elaborate a little more on "depending on the system and pump head vs. flow curves"? I'm asking the questions assuming everything stays unchanged, same system, no other pumps other than these two within the system, and they are identical pumps hence identical pump curves. Let's assume boiler doesn't exist or simply assume this is a closed system with nothing but two pumps in it. I'm just trying to draw a simple conclusion, if there exists. :)
  • hot_rod
    hot_rod Member Posts: 22,142
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    One way to know would be to create a system curve then overlay it on the pump curve(s)

    Some good pump basics, including how to develop a system curve in this journal.
    http://www.caleffi.com/sites/default/files/coll_attach_file/idronics
    \_16_na_0.pdf


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • bob_46
    bob_46 Member Posts: 813
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    Try this
    bob
    delta T
  • hot_rod
    hot_rod Member Posts: 22,142
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    bob said:

    Try this

    Nice! Even brings the System Syzer back to life :)

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream

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