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Positive vs. Negative Airflow - Page 2

post #11 of 43
look at silverstone case (raven, tf02), their cooling is absolutely briliant.
you have 3x18cm intakes and only one 12cm outake + holes in top panel...result? best air cooling on world imho
went from zalman gs1000 (3xoutake+1xintake 12cm fans) to raven.
CPU temps dropped by 7-8C
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post #12 of 43
I use negative pressure.
One 140mm in the bottom with filter and one 140mm at the rear and 3xNoctua P12 at the top pulling* hot air out.
Hot air don't need pulling to rise though.
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post #13 of 43
If you have a Big case lots of intake fans are good.

If you have a Small case you want Equal pressure. One intake and equal outtake combined with PSU exhaust is really good. Because the case is small ie: CM Elite, air is sucked by the exhaust fans from the front and pulled in low by the intake. This produces a low to high airflow stream through the case, which cools really well.

Large cases is harder to achieve an air-stream through one path and you need more fans and direction for the air to go.
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post #14 of 43
Excerpt from my guide listed in my sig:
Quote:
Positive

If you have more CFM coming IN, then OUT, you will have hot air cycling in your case waiting to go out, called positive air flow. However, most hot air will be pushed out through your available exhaust fans.

The benefit of having a positive pressure case is that all of your intake air is being cycled in strictly from your intake fans which should have dust filters installed. Therefore, a positive pressure case tends to have much less dust then a Negative pressure case.

Negative

If you have more CFM pushing air OUT than IN. This makes a negative airflow.

Basically you need more air OUT, then goes IN using the fans. The additional air needed will be sucked through the mesh and other holes in your case. The benefit, in theory, is that more cold air is being pulled in through the extra gaps and therefore keeping things cooler than a Positive pressure case.

Don't Go Overboard

Too much of one pressure can be a bad thing. Too much positive pressure can cause turbulent air inside your case and create pockets of hot air that can't escape in parts of your case. Too much negative pressure can prevent some components from getting any air flow at all. Try to attain a mostly neutral air pressure with a slight pressure change towards the pressure type you want to gain the advantages of that type.
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post #15 of 43
Quote:
Originally Posted by Gawdz;12725592 
This is just a debate forum i guess and too see what more people have.

Postive Airflow.
Postive airflow is having more intake fans then exhaust fans, this isn't real bad but then if you dont have enough exhaust fans air will be trapped inside your case then not having a real good airflow.

Negative Airflow.
Negative airflow is the opposite of postive airflow its having more exhaust fans then intake fans, this is good because its always taking new air into the case, but then you have more dust because the intake is mostly coming from gaps in the case and then causing trapped air.

The best airflow is probably a balanced airflow with the same amount of intake pressure as exhaust pressure!

Anyway this is just a debate between which is better!

You should always go for negative airflow--it's the most ideal situation for avoiding dead spaces, and ensuring that proper "fresh" air is reaching components that need it.

Also, one thing to correct, is that you stated:
Quote:
but then if you dont have enough exhaust fans air will be trapped inside your case then not having a real good airflow.
That doesn't really happen (unless you have a serious dead space in your case, which isn't too likely, and only a problem if the dead space is also a space that contains something you need to cool). The air might be exhausted slower than if you have more exhaust fans, but it won't really get trapped as there will always be airflow in and out.

The general rule of thumb is that you want slightly more fans (or more CFM) for exhaust than intake to ensure that you're properly dumping the heat outside of the case.
    
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post #16 of 43
I have 9 fans in my 800D.

- Three top-mounted 120mm fans exhausting
- Two 140mm fans at the bottom, intaking
- Two 120mm fans push/pulling a H50, intaking
- One front bay 120mm fan, intaking
- One side 120mm fan, HDD cage cooling
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post #17 of 43
I believe in positive airflow. On my cases I either buy one with no rear grill (typically aluminum) or remove the rear grill (steel). No exhaust fan. No slot covers on the backplane.

Negative pressure is like your vacuum cleaner. It's great for removing dust from your room and storing it in your case. Positive pressure creates stall points.

The virtue of positive pressure and positive airflow is that you limit your air intake to intake fans, which you can filter.

By having completely open spaces for air to escape no air pressure can really build up. It all flows.

See item 2 in my sig. It's an example of a negative airflow case. Because I left the rear open, the negative airflow was accomplished with cpu fans only. I was shocked that with so many open intake windows, they all showed negative pressure when occluded. It was a real kick.

But my rig run positive airflow. I practice what I preach.
post #18 of 43
I think positive pressure is better on the following merits:

1. Less dust buildup since most people have fan filters on their intake fans.

2. Cleaner and more predictable air flow, if you have too much exhaust it is sometimes hard to determine through which cracks and holes the extra air is being taken in from and it is therefore harder to make sure the clean air is going into the spots that need it.

That said neither is "ideal", ideally you would want a clean path from intake to exhaust going over all the major components, however the components are not perferctly aerodynamic and tends to mess with "clean" air flow. If you have too much negative pressure you will end up with a dusty case whereas too much positive pressure you can end up with places that tend to trap hot air.

Something that doesn't get brought up a lot but is very important in case air flow is how much air the GPU(s) dump out of the case. Furthermore, the fans on most modern GPUs are temperature dependent, so a case that has positive pressure could end up having neutral pressure under load.
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post #19 of 43
There's always going to be proponents of both methods, and neither one is "wrong". Negative pressure will always be more popular because most cases by default are set up for negative pressure.

That being said, I'm a convert to positive pressure. I hate dust and its amazing just how dust-free a positive pressure setup really is. The amount of dust my old P182 would build up in 30 days would take a year for my FT02 to accumulate. And as someone else said, the positive pressure Silverstone RV/FT series are some of the best performing air-cooled cases available.
post #20 of 43
I believe in POSITIVE! (Or at least I think this is positive tongue.gif) My Airflow.

Fan 1: Antec 902 200mm Exhaust Fan
Fan 2:Antec 902 Front 120mm Intake Fan
Fan 3:Antec 902 Front 120mm Intake Fan
Fan 4:Antec 902 Front 120mm Exhuast Fan
Fan 5: (Skipped this number on acident )
Fan 6: Coolermaster 120mm Exhaust Fan (Push/Pull)
Fan 7: Coolermaster 120mm Intake Fan (Push/Pull)
Fan 8: Scythe Slip Stream 120mm Intake Fan (Pull from fan 2)
Fan 9: Coolermaster PSU 120mm Intake Fan
Fan 10: Sapphire 6950 Intake Fan (Not sure if it suck or blows air, but I believe it sucks air in)

IMAG0026-1.jpg

What do you guys think? Good or bad??
Edited by WizrdSleevz - 3/14/11 at 9:53pm
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