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Thread: Dual Loop versus Single, the facts

  1. #1
    Mr Swiftech gabe's Avatar
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    Dec 2002
    Long Beach, CA

    Dual Loop versus Single, the facts

    The following series of tests represent Part II of the white paper published here

    In this article, the question we wanted to answer was:

    Are dual (dedicated) loops better than single loops?


    • Loop 1: MCR320 Drive radiator, with built-in MCP355 pump, and an Apogee XT waterblock; the loop uses ½ lines. The fans are Gentle Typhoon’s (D1225C12B5AP-15) running at 1850 rpm and rated at 28 dB.
    • Loop 2: MCR220 Drive radiator, with built-in MCP355 pump,Gentle Typhoon fans (same model) and 1/2" lines.
    • All components are connected to the loop with CPC quick-disconnect fittings; they are fairly restrictive, but the time they save in changing setups overshadows any other considerations.
    • The CPU is an early Ci7 920, Revision C0/C1 stepping 4.
    • The Graphic cards are (2) EVGA GTX470 FTW
    • The Motherboard is a Gigabyte EX58-UD3R, and the OS is Windows 7 Ultimate 64 Bit.


    • The CPU maximum stable overclock was well established, since we have been using this same 920 ever since its introduction. It is 4095 Mhz (Intel Turbo mode on, and HT enabled), at 1.424v (after droop).
    • The GPU’s maximum stable overclock was established in the previous graphics tests using Furmark in extreme burn mode at 1920x1050 for a minimum of two hours, and further validated by running 3D Marks Vantage.
    • Max stable overclock for 2 cards in SLI was 825 MHz core and 1000 MHz memory, @1.087 Volts.

    We conducted two series of tests, reflecting the following hardware configurations:
    • Series I, with the Ci7 920@ 4.1Gb and (2) EVGA GTX470 FTW in SLI @825/1000, and
    • Series II, with the Ci7 920@ 4.1Gb and (1) EVGA GTX470 FTW @825/1000.

    Within each series, we tested three cooling loop configurations:
    • Dual Loop with MCR320 Drive dedicated to cooling the CPU, and MCR220 Drive dedicated to cooling the GPU(s)
    • Dual Loop with MCR220 Drive dedicated to cooling the CPU, and MCR320 Drive dedicated to cooling the GPU(s)
    • Single loop combining MCR320 Drive, MCR220 Drive, CPU, and parallelly linked GPU's, in series

    Within each loop configuration, we simulated three load scenarios consisted in:
    • CPU load tests: In order to maintain consistency with previous test data, we ran our usual 8 instances of BurnK6. We logged the temperature results at 2 seconds intervals using CoreTemps. The average temperature of the 4 cores is reported.
    • GPU load tests: We used Furmark in extreme burning mode, windowed in 1920x1050, post processing off to enable 100% load to both GPU’s in SLI configuration, and logged the temperature results at 2 seconds intervals with GPUZ.
    • Combined CPU + GPU load test: We used (7) instances of Burn K6 + Furmark in extreme burning mode - The combination of these two benchmarks placed ~100% load on all four CPU cores, and a load on both GPU cores varying between 98 and 100%.
    • Graphics cards were hydraulically linked in parallel, as a result of the findings outlined in part I of this article.

    The test results are compiled and summarized in two groups: Temps under load in typical computer use, and Temps under load in Extreme computer use.

    • Typical computer use reflects the assumption that at the time of this writing, CPU maximum load and GPU maximum load are in the vast majority of the cases mutually exclusive of each other. In other words, the majority of games placing a heavy load on the GPU's use very few CPU resources, whereas the majority of CPU intensive applications use very little GPU resources.
    • The extreme computer use scenario reflects the currently rare occurrences where both CPU and GPU(s) are under maximum load.
    • Comparing these two groups provides an insight on the respective device load ratios relative to the heat exchangers and may provide guidance for further system configurations.

    Environmental Temperature recording:

    • Air temperature: each fan was equipped with a type T Thermocouples (accurate at +/- 0.1c) at the inlet, and the average of the 3 values is reported.
    • Coolant temperature was measured at the radiator inlet with a Type T thermocouple (accurate at +/- 0.1°C).

    Series 1 test results, CPU + SLI configuration:


    Under typical computer use, the above test data suggests as a general rule that users would not benefit from setting up dedicated loops for CPU and GPU. Serializing pumps in the same loop also adds a redundancy factor that dedicated loops cannot provide. With superior reliability and lower temperatures at both CPU and GPU levels, single loops appear to win hands down.

    Under extreme computer use, this setup recorded a notable advantage at the CPU temperature level for the dual loop, counterbalanced by the opposite effect at the GPU level. This extreme environment uncovered the critical importance of the respective load ratios generated by CPU class devices vs. GPU class devices, relative to the heat exchangers to which they are connected. Clearly, a CPU generating 150 Watts solely dedicated to a triple radiator will cool substantially better than when mixed with another 400 watts generated by two GPU's even with a second dual radiator in the loop. Jedi Masters would say, "we need to bring balance to the force here", and they would be right.

    We could define a simple mathematical method to properly configure a system accounting for loads, but that will be for another article. For now, we can simply illustrate the above in real life testing by removing one of the GPU's from the system. It has for effect to balance the heat load generated by CPU device more evenly against that of the GPU device and demonstrates how load ratios affects the results:

    What we see above is that even under extreme use, the dual loop has all but lost its performance advantage against the single loop. Incidentally, the same type of trend could have also been obtained by adding a second CPU in the loop instead of removing a GPU.


    Under extreme performance scenarios, and from a pure performance standpoint, dual loops versus single loop are neither better nor worse, under the strict condition that the load ratios are evenly balanced.
    Under the most commonly encountered loads though, single loops do win.

    Under both of the above use scenarios, single loops also win from a reliability standpoint because of pump redundancy.

    The choice is yours to make.
    Last edited by gabe; 07-23-2010 at 11:29 AM.
    CEO Swiftech

  2. #2
    Admin Vapor's Avatar
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    Feb 2005
    Ann Arbor, MI
    I love it! Great stuff with this practical use testing you're doing, Gabe

  3. #3
    Mr Swiftech gabe's Avatar
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    Dec 2002
    Long Beach, CA
    Quote Originally Posted by Vapor View Post
    I love it! Great stuff with this practical use testing you're doing, Gabe

    Thanks I hope it will help readers to make informed setup decisions.
    CEO Swiftech

  4. #4
    Xtreme X.I.P. Martinm210's Avatar
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    Jun 2007
    Bend, Oregon
    Thanks Gabe...great stuff here!

    Still not sure why I'm still running dual loops..maybe I'll go back to one after the next rebuild...

  5. #5
    Moderator shazza's Avatar
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    Aug 2007
    Back and forth between Florida and Maine
    Thanks for the data, gabe.

    I recently switched to single loop and it seems to be working well - unfortunately, I was too lazy to do the proper comparison testing so it's good to see your results.

  6. #6
    Xtreme Enthusiast Danger30Q's Avatar
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    Mar 2005
    Madison, WI
    That was absolutely fantastic. I appreciate you sharing the results with us here at XS.

    This helps me on my decision for either running a single or dual loop on my 920 and 480s in SLI.

  7. #7
    Xtreme PITA to MM Fitseries3's Avatar
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    Nov 2007
    so my single massive loop will be plenty sufficient it seems.

    glad to hear.

  8. #8
    Registered User
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    Feb 2008
    Dare I post among these giants of the group....

    Interesting read. Nice work...

    However, Trekkies, don't talk about the force, that's Star Wars...

    But THANK YOU for not calling us Trekkers. I wish they had never started that.

  9. #9
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    AWESOME! Thanks Gabe.
    Core i7 920 @4.31ghz (HK3.0+MCR320Drive) [DT Air/CPU @ 13c idle, 45c IBT]
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  10. #10
    Xtreme Member avddreamr's Avatar
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    May 2008
    That's a fantastic post. I wonder what the power draw is at load?
    @Gabe: How much do you feel that temperatures would suffer under the following conditions:
    Dual MCP350's instead of dual 355s?
    Or using a single MCP 350.
    I would imagine that it would be quite easy for one of your many clients to add a dual radiator to their existing loop with your products.

  11. #11
    Xtreme Addict Blacky's Avatar
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    Jan 2008
    Puerto Rico
    Wow thanks gabe I was thinking going dual loop for my setup but this has proven otherwise !
    ░█▀▀ ░█▀█ ░█ ░█▀▀ ░░█▀▀ ░█▀█ ░█ ░█ ░░░
    ░█▀▀ ░█▀▀ ░█ ░█ ░░░░█▀▀ ░█▀█ ░█ ░█ ░░░
    ░▀▀▀ ░▀ ░░░▀ ░▀▀▀ ░░▀ ░░░▀░▀ ░▀ ░▀▀▀ ░

  12. #12
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    Nov 2004
    I appreciate seeing hard data on loop water temperatures, thanks Gabe.

  13. #13
    Xtreme Mentor Conumdrum's Avatar
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    Oct 2007
    Hmm, anyone want to buy my extra DDC XSPC restop? Used, good shape.

    Thanks Gabe, great info. You said you'd be reworking it, you sure did.
    All stock for now, no need for more, but it's gonna be soon methinks.
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  14. #14
    Registered User Raychem's Avatar
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    Oct 2009
    Great article Gabe!!!! Just what I was looking for as far as large single loops are concerned. Thanks for your contribution.

  15. #15
    Xtreme Addict ScottALot's Avatar
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    Feb 2010
    UW - Madison
    Great guide! I still wonder, though... is it better to have two pumps under one top at one point in a loop, or two pumps at different points in a loop?

    Also, there's probably a really good guide out there, but I can't seem to find one: Anyone know how much of a performance gain you get with two pumps under one top instead of just one pump?
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  16. #16
    Xtreme Member zigzag's Avatar
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    Newcastle upon Tyne (UK)
    Wow, thats great as im gonna be doing 1 masive loop either today or tomorrow

  17. #17
    Xtreme Cruncher WhiteFireDragon's Avatar
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    Jul 2007
    @ the computer
    awesome review! looks like single loops wins. now if you were to add one more twist, which one would win in this scenario: a single combined loop with only one pump, or a two separate loops with a pump in each loop? basically, the only thing that's changed is that the combined loop with one less pump. taking one pump away would mean less pressure/flow, but that also means that the heat from that pump is not dumped into the loop. so now, any ideas which one would win?

  18. #18
    Xtreme Member imersa's Avatar
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    Feb 2010
    Really good read. Some good results. Makes me wonder why I have two loops at times...
    Yeah that would be an interesting thing to find out @ScottALot

  19. #19
    Xtreme Addict Alexandr0s's Avatar
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    Nov 2009
    Great test Gabe. Good to see I wasn't wrong when suggesting single instead of dual loop to others .
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  20. #20
    Xtreme Member Biffa's Avatar
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    Jun 2010
    I'd be interested to see how the dual pump/single bayres perform in this sort of scenario, there you have a single water source but pumps pushing that same water round two differerent routes.

  21. #21
    I am Xtreme Zeus's Avatar
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    Feb 2003
    Good! Another very informative post, big thumbs up.

    I never really understood the multiloop train of thought other than decreasing restriction. With restriction in mind, a single loop with just one pump like suggested is what i would really like to see as that is what i'm using atm.

    How important is flow for a sinlgle loop, especially with 2 videocards?

    Keep up the great stuff Gabe!
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  22. #22
    Xtreme Member
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    Sydney, Australia
    Very nice information, thanks for testing!

  23. #23
    Xtreme Member Kvickstick's Avatar
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    Mar 2010
    Wow, no need for dual loop then!
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  24. #24
    Xtreme Member JoeChuo's Avatar
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    Jun 2009
    Strange ... I thought everybody knew this already?
    Yaay! Again! Single loop looks better too!

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  25. #25
    I am Xtreme Waterlogged's Avatar
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    Imperial Palace, UDE of Pitatopia
    Nice testing indeed. . .but, all these results are with 355's. I'm curious what would happen to the results if 655's were used instead. There are those out there that flat out refuse to use DDC's for whatever silly reasons they believe in and this testing really doesn't help them.
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