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  #1  
Old 03-30-2013, 07:06 PM
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Default Push Hot Air In or Out?

Being a racing engineer concerned with heat loading of extreme degrees, in all manners of the word, pushing hot air into a volume never made sense to me. Sure, the one component that the radiator is attached to is better cooled by having a larger temperature differential but the other components are negatively impacted by this one situation. Overall, the system suffers.

Motherboard is P9X79 Deluxe with an i7-3930K and 32GB Dominator Platinum. Graphics card is GTX670 in a 650D with a 200mm front intake fan and 120mm exhaust above the expansion slots. Cooler is H100i set to push out through the radiator mounted to the large top vent. AX1200i PSU is mounted with intake fan down, thereby insulating its heat from the case interior through its own closed air loop to the outside. Three thermocouples monitor temps at the top of the case between the 5.25" bays and radiator, inside the HD cage and just over the PSU in the bottom rear.

Temps were OK but I felt that there was room for improvement. I studied the readings on all of the components for a few days and adjusted a couple of profile custom curves to see what I could wring out of it. Once I had that baseline, I made one change. Took the 120mm exhaust that is mounted adjacent to the motherboard and over the expansion slots in the rear and turned it around to push cool air in. This cool air flows directly across the memory and passive motherboard heat sinks, directly upon the radiator coolant hoses and into the intake of the H100i exhaust push fans; supplying them with cool air that has traveled only a sort distance.

Case is now under positive pressure, which increases the flow of the SP120 fans pushing air through the radiator. They are no longer pulling against the neutral or negative pressure, so their efficiency is greater, as is the resultant energy transfer between mediums.

From this one small refinement in energy management:
  • CPU Temp Dropped 5.5C
  • Water Block Temp Dropped 6C
  • Motherboard Temp Dropped 6C
  • GTX 670 Dropped 4C
  • AX1200i PSU Dropped 1.5C
  • Upper Case Thermocouple Dropped 3C
  • Lower Case Thermocouple Dropped 4C
  • Drive Cage Thermocouple Dropped 1.5C
  • SSD and HD Temps Dropped 1C
  • Fans All Slowed

After monitoring this for a period, I refined the fan RPM profiles to extract the best performance with lowest dB levels.

As a fun thing, I have the original 200mm top exhaust fan that came in the 650D that had to be removed to mount the radiator sitting on the top of the case over its original mounting holes. It turns lazily from the air flow emanating from the case vent and provides a little bit of animation; looking much like the huge fans that turn in the distance in a lot of films. With this new configuration, it turns twice as fast or more; a testament to the increased flow and efficiency.

Pretty cool, to make a pun.

Last edited by Speed; 03-30-2013 at 08:24 PM.
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  #2  
Old 03-30-2013, 07:26 PM
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cooling is cooling,be it car or computers
every mph,err degree matters
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  #3  
Old 03-31-2013, 06:17 AM
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Great post!
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Old 03-31-2013, 09:59 AM
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Have that since the beginning, not only because of cooling performance but also because of the dust (add a filter to the back fan)
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Old 03-31-2013, 10:55 AM
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Already on there. Made one out of a sheet of thin open cell foam. Domed it like an airplane hangar to increase the surface area so as to not starve the fan. Testing before building, the fan spins about 30 RPM faster when the foam is placed directly on the grille, indicating that it is not getting the full amount of air possible and, hence, doing less work, so spins faster due to less resistance. Surface area on the domed foam is 117.375 sq. in. That's 5.33x the fan input grille cross section, as it covers the entire flat panel where the fan port is on the 650D, from case top to expansion slot cavity and left side to ports cavity. Measures 1" tall along the vertical edges and domed 3" on the horizontal edges. Place the filter on, no change in RPM and cannot feel any difference in throughput on the inside, on or off.

Anything close to the input side of a muffin fan will severely throttle its throughput. The farther away, the better. Input grilles do this and people never give them a second thought. They are incredibly "dirty", turbulence-wise. Standing fans off from their normal surface mounting position by only .5"-.75", using a cylinder to close off the gap--creating a short tunnel, makes a huge difference in efficiency. Corsair cases go part way in this manner by doming the grille a bit to get the metal away from the blades. More is better.

Here's a little test that you can do that illustrates the principle. Get a fan out of the case, hold it so that it is blowing on your cheek, slide a pencil or small dowel sideways across the input face of the fan. You can tell where on the fan the pencil is by feeling the change in flow on your skin. It's remarkably precise. That small an object slices a long hole in the air. Keep doing the lateral movement of the pencil while successively moving it away from the fan input opening with each pass. At a short distance, you can no longer feel the change made by the pencil disturbing the flow of air to the blades. They are working at their maximum, undisturbed by the turbulence that the pencil creates. The pencil is still there, but because there is enough distance for the turbulence to dissipate, dampen and return to flowing smoothly again, it no longer makes a difference.

If the air going in is restricted and isn't smooth, the blades cannot do their job effectively, because they're the wrong shape for what they are being given.

Set your fans free. They'll love you for it.

Last edited by Speed; 03-31-2013 at 11:15 AM.
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  #6  
Old 03-31-2013, 01:01 PM
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so the only exhaust on your case is thru the h100? im setting up mine, i have two af120 in the front for intake, two af140 on the side for intake, and i was going to do a 140 on the rear for exhause as well as set my h100 to exhaust. think it would be smarter to do my rear as intake instead of exhaust?
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Old 03-31-2013, 01:20 PM
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Great thread dude!!

A few weeks back, my rear exhaust fan started making an awful rattling noise, I removed the fan and ordered a new one..

While I was waiting for my new fan to arrive, my 600T was running without a rear exhaust fan. I began to notice lower temps pretty much on all components, I was like .

My 680s use to hit 88c & 82c while playing Crysis 3 and now the top card is maxing 79c after hours of gaming!!

I didn't install the new fan yet but it makes sense that the top radiator fans are struggling for air when the rear fan is set as exhaust.

Thx for this thread!
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  #8  
Old 03-31-2013, 02:08 PM
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Quote:
Originally Posted by excaka View Post
so the only exhaust on your case is thru the h100?
Yep. The 650D top vent is large enough to fit an H110, so there is about 1" on all sides of the radiator of static vent. I usually block things like this off, in order to keep a fan from recirculating air around the sides and reducing the net throughput. Normally, a fan needs to be the only passage through an interface or it sees some of the same air over and over. With the configuration described above, if I drop a facial tissue on the perimeter vent area, it lifts and eventually blows right off. The highest throughput, of course, is through the radiator in the center. Nice amount of gentle warm air flows from the entire opening at idle and a good blast flows under load.

Additionally, I set that rear intake into the CPU group in CorsairLINK2.3. When the CPU is at or near idle, the rear intake provides general motherboard, memory and CPU cooling. When the CPU comes under load, it ramps up along with the H100i to give the radiator a boost. It doesn't respond as quickly as the H100i SP fans but if the load is there for any significant length of time it gets up to its max and levels off the CPU heat increase.

Just remember to do a gross CFM computation on in vs out. Too much of a good thing can be as bad as not enough. IOW, if you have too much CFM in in relation to the number out, the in fans will cavitate because they are aerodynamically stalled from the pressure. They can't do their job because they can't move anything. Same thing as the starving input concept mentioned above, but on the other side of the fan. It's the reverse of the H100i fans pulling against negative pressure.

Quote:
Originally Posted by excaka View Post
im setting up mine, i have two af120 in the front for intake, two af140 on the side for intake, and i was going to do a 140 on the rear for exhause as well as set my h100 to exhaust. think it would be smarter to do my rear as intake instead of exhaust?
I'd say so. It'll depend a lot on the relative speeds of each and tuning the 120s and 140s will make a lot of difference. Just don't overdo it. With your set up, you could probably drop the speeds of all of the intake fans quite a bit and lower the noise, while maintaining thermal balance.

In general, helping those static pressure fans is a good thing. They have a hard enough job as it is and with a positive pressure case, dust won't enter through the myriad of holes and cracks. I seal off the big & medium ones with tape but gaps around external connectors, ports, DVD drawers, case panels and the like all let crud in that eventually coats your hardware, most specifically the passive heat sinks and memory sticks that need to be clean to function at their best. Keeping dust out of your video card fans and fine fins is a definite plus. Just be sure to craft a good air filter with plenty of flow headroom for all intakes that don't already have one.

Last edited by Speed; 03-31-2013 at 02:43 PM.
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  #9  
Old 03-31-2013, 02:18 PM
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Quote:
Originally Posted by VasVas View Post
Great thread dude!!
Thanks.

Quote:
Originally Posted by VasVas View Post
A few weeks back, my rear exhaust fan started making an awful rattling noise, I removed the fan and ordered a new one..

<snip>

I didn't install the new fan yet but it makes sense that the top radiator fans are struggling for air when the rear fan is set as exhaust.
Get things working on concert and lots of good stuff is just waiting to reveal itself. Even with nothing it works better. Dontcha just love science?

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Thx for this thread!
You're welcome.
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  #10  
Old 04-23-2013, 02:17 AM
Nec_V20 Nec_V20 is offline
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Speed,

very good posts you wrote. The practical fact of the matter is that one just cannot keep all the grot out of the case. However grot accumulates on the fans as can be seen here:

I keep an eye on the temperatures but my system is a workhorse and not a prancing horse and it runs 24/7 and has done so for about two and a half years now.

I will be giving it a good clean out in the next couple of weeks. There is however nothing wrong that a bit of liquid air, a vacuum cleaner and toothbrush can't cure

I have however tried to arrange it so that I have positive pressure (blowing air out of the casing) where there are holes and negative pressure (sucking in the air) where I have filters.

My computer is however, as I stated, a workhorse. I can play any game I want for as long as I want and the CPU temp has yet to go above 60 degrees. The graphic card also stays well within the temperature tolerances. I don't give a toss about framerates as long as I do not notice anything interrupting the flow of the graphics. Anything beyond that is superfluous, just a value to give ones self bragging rights.
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Last edited by Nec_V20; 04-23-2013 at 02:34 AM.
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  #11  
Old 04-23-2013, 10:40 AM
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this is a good post..
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  #12  
Old 04-29-2013, 12:05 PM
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I was worried thinking about this config, that all cool air pushed by the rear fan into the case will be directly sucked by the H100i fans and would not have any impact over the MoBo and/or memory, I will use a H100i push/pull configuration (4 fans), do you think it will work the same way as you explain?
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Old 04-29-2013, 01:25 PM
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As others already said, great and very interesting post!

I just replaced my old H100 which was defective with a H100i and I'm currently trying to figure out what fans would be best for it since I find the fans that come with the H100i very loud under load. On my old H100 I used Scythe GT 1850 rpm fans and I think they worked great but now with my new H100i I want PWM fans. At the rear of my 650D I still have a Scythe GT 1850 installed as exhaust but I would like to replace this fan as well with a PWM fan so I can control that one too within Corsair Link.

I've been looking at the Corsair SP120 PWM fans, not sure if choosing them I should go for the performance edition or the quiet edition. Then I also read about Scythe Glide Stream, there are two PWM models...1400 rpm and 1900 rpm. Looking at their specs they seem to move a lot of air without making to much noice but not sure how good they would work as radiator fans and I also wonder if they would be fully controllable within Corsair Link - is the fact that they are PWM fans a guarantee for that or does the fan need to be compatible with Corsair Link is some way to be fully controllable?

Then for the rear fan one thing I was thinking about when reading your findings using it as intake rather than exhaust, I wonder what would work best looking at the Corsair fans for example...to use an AF series fan or a SP series fan...?

Very interesting all this with fan configurations!
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  #14  
Old 04-29-2013, 11:46 PM
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Fan types and what's best for the application:

http://forum.corsair.com/v3/showthread.php?t=118043

That said, I don't have PWM fans yet and they are all controlled by CorsairLINK.
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Old 04-30-2013, 03:01 AM
WebMaximus WebMaximus is offline
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Thanks for the link.
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