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post #11 of 15
Quote:
Originally Posted by max it View Post
If there's constantly more air coming in than out, won't your case explode after a while? I should think that the pressure inside would increase to a certain level before the pressure decreases the cfm and increases the static pressure? And increases the flow outwards.

more intake = less outtake? = more pressure = lower airflow = more outtake? = high airflow?
(something went wrong there)

...might seem confusing, but it all reaches an equilibrium where everything stays the same, until you change the rpm of a fan or something.
Think of it more along the lines of whether air is being pushed (Positive) or sucked (negative) into your case.

If your system is positive pressure, you have more intake CFM than exhaust, which will push air out all the cracks and grills in your case as well as causing your exhaust fans to operate against a lower resistance than your intakes.

With a negative pressure system, air tends to get sucked in rather than blown out. That's generally undesirable because it allows dust into your system through all of the un-filtered openings in your case.

Ideally you'll be mostly balanced, with a slight bias towards positive pressure to keep dust out.
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post #12 of 15

As for your case airflow question, you would use the total CFM IN vs. total CFM OUT to figure out what kind of pressure you have. IN>OUT=Positive, OUT>IN=Negative.
Just add up up the CFM of all the intake fans and compare it to the CFM of all the fans that exhaust, including the power supply and GPU fans.


Static pressure has more to do with fans on heatsinks and radiators. Static pressure is a measurement that can tell us how well a fan can push air through a restrictive barrier i.e. the fins of a heatsink or radiator. Fans with weak static pressure just move air from one side to the other, but fans with higher static pressure move that air in a more concentrated stream. This video will explain it better....


Edited by spaceballsrules - 3/28/11 at 10:38pm
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post #13 of 15
if your ambient is colder then your rig you want positive..
if your ambient is hotter then your rig you want negative thats all there is too it I think..
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post #14 of 15
Quote:
Originally Posted by F-U-B-A-R View Post
if your ambient is colder then your rig you want positive..
if your ambient is hotter then your rig you want negative thats all there is too it I think..
What?



@RoddimusPrime - You want as close to a 50/50 split of CFM In vs. CFM Out as possible while leaning ever so slightly towards positive or negative. Both have advantages and disadvantages.

Positive - You can control all dust at the intake fans with filters, but you risk creatng hot-spots in the case or simply recirculating hot air within the case, as it has no way to escape.

Negative - Dust gets in through every crack, crevice, and orifice it can, but you minimize hot-spots and hot air is efficiently evacuated from the case.

It is up to you to choose which you want by configuring the airflow in your case. Can you live with a little dust to get 1 or 2*C better load temps?
Edited by spaceballsrules - 3/28/11 at 10:57pm
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post #15 of 15
Thread Starter 
Quote:
Originally Posted by spaceballsrules View Post
As for your case airflow question, you would use the total CFM IN vs. total CFM OUT to figure out what kind of pressure you have. IN>OUT=Positive, OUT>IN=Negative.
Just add up up the CFM of all the intake fans and compare it to the CFM of all the fans that exhaust, including the power supply and GPU fans.


Static pressure has more to do with fans on heatsinks and radiators. Static pressure is a measurement that can tell us how well a fan can push air through a restrictive barrier i.e. the fins of a heatsink or radiator. Fans with weak static pressure just move air from one side to the other, but fans with higher static pressure move that air in a more concentrated stream. This video will explain it better....
http://www.youtube.com/watch?v=8m8fC809TK0
That is pretty slick. I could see how some literally just move air (CFM focused) while some were in between, and the AP had a focused stream (static pressure). I had read about that of course, but it was nice to see in action. Had a hard time believing fans have that much different of a technology. I imagine thickness, number, and angle of blades have a good amount to do with how the air is moved and in what direction/directions the air is pushed in. Obviously on an exhaust this would hardly matter. But, perhaps on an intake like the Silverstone FT02 or a radiator/aftermarket cooler which require more force.

Quote:
Originally Posted by spaceballsrules View Post
What?



@RoddimusPrime - You want as close to a 50/50 split of CFM In vs. CFM Out as possible while leaning ever so slightly towards positive or negative. Both have advantages and disadvantages.

Positive - You can control all dust at the intake fans with filters, but you risk creatng hot-spots in the case or simply recirculating hot air within the case, as it has no way to escape.

Negative - Dust gets in through every crack, crevice, and orifice it can, but you minimize hot-spots and hot air is efficiently evacuated from the case.

It is up to you to choose which you want by configuring the airflow in your case. Can you live with a little dust to get 1 or 2*C better load temps?
Yeah, I guess I might be surprised on how much dust a case might collect from nooks and crannies if it were negative pressured versus potential heat being trapped with positive pressure. Mind you I know there isn't a whole lot of pressure in a case regardless, esp. compared to the room it is in typically. However, if you had a fairly similar amount of air going in as coming out it would probably be best to create a constant airflow and avoid the problems of either. I know wind tunnels use that idea in order to keep a constant pressure and for a controlled environment when testing things.

+rep
Edited by RoddimusPrime - 3/29/11 at 7:12am
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