Negative pressure concern

dragonmike

dragonmike

dragonmike

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23 Feb 2015
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Hello guys, I built a custom watercooling loop a few months ago... but the more i look at it, the more I question my airflow decision...

I'd like to know what you guys think of my fan setup... I'm a bit concerned I might have negative airflow in my case - here's an MSPaint sketch (components with a waterblock on in red):



Do you think I should add a bottom intake fan?


Cheers!
 
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I would add more intakes myself, but that's just me.
I'm a bit concerned about your PSU, though - Most seem to prefer it intake from the underside and exhaust out the back - Some have it intake from within the case, but I'm not a fan of that.
 
Actually, my PSU airflow arrow is wrong. It takes air from underneath and expells it out the back... I'll have to amend that in MSPaint! :D

EDIT: sorted
 
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The rear bitfenix - I would be tempted to reverse that so that it is pulling in more cool air which will help cool your top mounted radiator.

I don't know if it will make a great deal of difference tbh but worth a try.
 
Another thing to consider changing is your front fans. if doing push pull you should be using matched fans but you have different fans pulling than you do pushing. They have different rpm's and different amount of air they shift. Pair them up so that you have the same fan pulling and pushing.
 
I doubt very much whether it would make any discernible difference - cases are not airtight enough to cause cavitation and you have 4 fans working as pairs in push pull at the front.
 
It's a Corsair 750D case.
I kept the AF140's that were given with the case in front... I could swap them for a pair of SP140's indeed but I kept it like that mostly because of laziness!

I think I might swap the Bitfenix around indeed. Although one usually says the top fans should be exhaust fans, in this case I think the 3x120's at the top might just do that well enough, and I like the idea of blowing cooler air directly onto it.
 
If you are feeling lazy to buy a matching pair for the front, I would have thought for the time being you would be better off having the SP fans at the front, with the airflow fans at the back.

If you do make the rear an intake, get a dust filter on it :)
 
Lazy might have been too strong a word! :p Rather eager to get the build done asap! I'll probably swap those AF's out for SP's in the near future. Good point on the dust filter.
 
EK's PWM version of the Laing D5. It's just really strong and reliable. Got the EK VRM block, EK Evo Supremacy CPU block, EK full cover GPU blocks (connected with a parallel terminal). Works a treat. Using a separate res as well. Here's a picture of the pc while I was still building it (no real cable management yet and still had the ugly white fan on top):



The 750D is a nice case but it is not massive. Had to do some proper space management.

The third GPU is dead, unfortunately... Rust in pieces. The idea is to get a new, better GPU a few months down the line. I had these 280x's lying around from an old build.
 
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Tattysnuc said:
I doubt very much whether it would make any discernible difference - cases are not airtight enough to cause cavitation and you have 4 fans working as pairs in push pull at the front.
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If you have faster fans Pushing than those Pulling, you can cause turbulence and compression stalls, which hamper performance and can damage either/both of the fans, particularly through radiators. Going the other way around (slow Push, fast Pull) can work, but for this level it's simpler and easier to keep both the same.
 
Hmmm you have got methinking,my setup has negative pressure while idle,but when placed underload and my PWM curve kicks in it turns positive.

Fink i will flip my rear out to an intake and see if it offers any improvement.
 
Five.Stars said:
The rear bitfenix - I would be tempted to reverse that so that it is pulling in more cool air which will help cool your top mounted radiator.

I don't know if it will make a great deal of difference tbh but worth a try.
Click to expand...

thats what i do aswell fella. I have 2 140mm fans in the front feediing the bottom 360 rad and 1 140mm fan in that position feeeding the top 360 rad. Case is primo btw.
 
I always have more air exhausting than coming in air cooling.

But on your set up l would have both rads air out, bottom front rad air blowing out same as top.

Why heat the inside of the case with hot air from bottom front rad.
 
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I have a similar setup to yours. Regardless of negative / positive pressure Ive found that if I have the rear fan as an exhaust the internal air temp is 1-2 degrees higher ( I have a temperature sensor just below my top rads). So on this basis ive found its better to use the rear fan as an intake as this means cooler air passing through the top radiator
 
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