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Discussion Starter · #1 ·
I got to thinking about ways to reduce or eliminate unwanted dust from being drawn into a PC case via intake fans. Thus, I would like to proffer a solution that may or may not be well-known or understood in regards to a clean PC operating environment. It has to deal with positive air pressure flow within a PC case.

Sometimes, more is not better. Having oodles of powerful intake and exhaust fans in a case are not going to keep dust from entering a system, and oftentimes, they do a poor job in cooling the system anyway. Simply throwing fans at a dust/cooling problem isn't going to solve it, and more logical and effective methods will need to be incorporated to truly keep the inside of a PC case both clean and cool.

With this in mind, for those serious about clean PC's, you may want to look into the use of positive air pressure in a PC case. Positive air pressure simply means that more intake air is forced into the chassis than air is being exhausted. This might sound contradictory at first, but if you think through it, it will make sense.

It goes something like this: If there is more air entering the chassis than exiting, you have a positive air pressure environment. This happens when your fans are intaking more air than being exhausted. This surplus of air will push air out of the case through the many cracks inside a chassis. This positive air pressure essentially prevents dust buildup where there are no fans. I'm sure everyone has experienced dust buildup in places such as the CD/DVD bays or the PCI slot area. These areas and others are notorious for dust build up where fans are not used.

However, if you have more air being exhausted than taken in, you have a negative air pressure environment. This happens when your fans are exhausting more air than being taken in. What occurs here is dirty, unfiltered air is being drawn through the cracks within an enclosure. This condition creates dust buildup within an enclosure very quickly. The problem is only exacerbated because this unfiltered air cannot be contained or filtered in any way.

If you intend to use a positive air pressure design in your chassis, using fans that offer high static pressure such as Silverstone's excellent Air Penetrator series (http://www.silverstonetek.com/product.php?pid=257) will help tremendously in this regard. These types of fans have higher mmH20 than most, and can increase the positive pressure inside a chassis considerably while keeping operating temperatures in check at the same time.

The one constraint when employing positive air pressure within a PC enclosure is that the intake fans MUST have good filters installed on them. This cannot be stressed enough! 3M filters meant for HVAC systems that are then cut to size are an extremely good choice and what I use in my own systems.

For more information concerning positive air pressure versus negative air pressure, check out Silverstone's TechTalk link (http://www.silverstonetek.com/techtalk_cont.php?area=en&tid=wh_positive). It has a nifty animation showing how both positive and negative air pressure interact in a typical PC enclosure.

If any of this was helpful to anyone, please feel free to chime in! Thoughts and comments are always welcome. Thanks!
 

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Positive pressure will reduce dust from being drawn in but in reality all you need is neutral case pressure, not positive pressure. Negative pressure is what draws all the dust in around case openings. Neutral pressure will not draw in dust.

In reality any normal fans will work fine. You don't need high pressure fans. Good intake filters help reduce dust dramatically but make sure they are not too restrictive.
 

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I agree with the OP. Not only will it keep you rig cleaner, it will improve cooling performance especially on radiators setup as exhaust. I have two 140mm fans on my side panel and my temps actually increase when I remove it.
 

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Discussion Starter · #4 ·
Neutral case pressure? I'm not sure if there is such a thing, or if that is even acheivable. Either you have positive or negative case pressure. If you had "neutral" pressure, there would be zero air pressure within the enclosure, that is, no airflow within the chassis itself.

In any event, dust is a problem regardless of which air pressure method you use, positive or negative. Granted, positive air pressure lessens the liklihood of dust accumulating inside a computer chassis, but without a quality filtration system in place, as you mentioned, the benefits of a positive air pressure system in an enclosure is largely wasted.
 

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Quote:
Originally Posted by garetjax27 View Post

Neutral case pressure? I'm not sure if there is such a thing, or if that is even acheivable. Either you have positive or negative case pressure. If you had "neutral" pressure, there would be zero air pressure within the enclosure, that is, no airflow within the chassis itself.

In any event, dust is a problem regardless of which air pressure method you use, positive or negative. Granted, positive air pressure lessens the liklihood of dust accumulating inside a computer chassis, but without a quality filtration system in place, as you mentioned, the benefits of a positive air pressure system in an enclosure is largely wasted.
Of course you can have neutral pressure. It's when the inside and outside pressure are the same like when the PC is turned off. You can also have intake and exhaust fans that create the same pressure/flow and air flows constantly thru the case.

People often confuse air pressure and air flow. You can have positive pressure and little or no air flow thru the case. You can also have negative pressure and little to no flow thru the case. That's why air flow is much more important than air pressure when it comes to cooling PC hardware.

Negative pressure is not desirable because the fans will suck air in where ever it can and that means thru any opening, which means dust comes in from all openings. This is very easy to see after just a few weeks of operation.
 

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Quote:
Originally Posted by AMD4ME View Post

Quote:
Originally Posted by garetjax27 View Post

Neutral case pressure? I'm not sure if there is such a thing, or if that is even acheivable. Either you have positive or negative case pressure. If you had "neutral" pressure, there would be zero air pressure within the enclosure, that is, no airflow within the chassis itself.

In any event, dust is a problem regardless of which air pressure method you use, positive or negative. Granted, positive air pressure lessens the liklihood of dust accumulating inside a computer chassis, but without a quality filtration system in place, as you mentioned, the benefits of a positive air pressure system in an enclosure is largely wasted.
Of course you can have neutral pressure. It's when the inside and outside pressure are the same like when the PC is turned off. You can also have intake and exhaust fans that create the same pressure/flow and air flows constantly thru the case.

People often confuse air pressure and air flow. You can have positive pressure and little or no air flow thru the case. You can also have negative pressure and little to no flow thru the case. That's why air flow is much more important than air pressure when it comes to cooling PC hardware.

Negative pressure is not desirable because the fans will suck air in where ever it can and that means thru any opening, which means dust comes in from all openings. This is very easy to see after just a few weeks of operation.
Maybe I'm doing the above, but wouldnt positive air pressure cause a buildup of hot air since it's not being exhausted fast enough?
 

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This is been debated for years, maybe since the beginning of time...

Personally I've always felt running a slight positive pressure was better. However, there are endless debates on this topic, and without actual controlled testing, it's difficult to prove anything.
 

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Originally Posted by B3anbag View Post

Maybe I'm doing the above, but wouldnt positive air pressure cause a buildup of hot air since it's not being exhausted fast enough?
You can have positive pressure with plenty of air flow - which is why I tell people to ignore pressure per se and just make sure they have good air flow thru their PC case for proper cooling.

Positive pressure does not automatically mean insufficient exhaust flow. It means the inside case pressure is higher than the outside case pressure. That doesn't tell you anything about how much air flow there is.

Negative pressure does not mean that you have sufficient or insufficient air flow either - but it does mean that you will draw in dust at every tiny and large opening in the PC case. This is why neutral or slightly positive case pressure is desirable. Air pressure is not air flow.

As noted the only way to tell if you have sufficient air flow be the case pressure positive or negative, is by carefully checking temps.
 

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How do you know if your case is high or low pressure? Also, how does one go about having a higher pressure case?
 

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Quote:
Originally Posted by Houston View Post

How do you know if your case is high or low pressure? Also, how does one go about having a higher pressure case?
By having more intake fans then exhaust fans I.E. 2x120mm fans in 1x120mm fan out this is of course considering they are both the same fans and the case is enclosed I.E. no mesh sides that the air can escape etc.
 

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Quote:
Originally Posted by Houston View Post

How do you know if your case is high or low pressure? Also, how does one go about having a higher pressure case?
It's not high pressure vs. low pressure per se, it's positive vs. negative pressure. There is no need for "high pressure" as that would require noisy fans and not serve any useful purpose. All you need is neutral to slightly positive pressure to keep dust out.

Scientifically you can use a pressure gauge, typically rated in inches of water, to measure the differential pressure.

If you want a simple layman's approach just open your PC case and look around the small openings around drives or case edges and look for dust trails. If you do not see where dust is being sucked in, chances are very good that you have a positive pressure situation that prevents dust from being sucked into your case other than thru intake fans. You will typically see small dust trails near the fans even with good filtration.
 

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Ah, thank you. I was under the impression that if you truly had a positive pressure case you wouldn't have any dust but you clarified that up.
 

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I believe in positive flow, not positive pressure. Positive pressure can cause stagnation and impair cooling.

I'm a big <ahem> fan </ahem> of adding a 5.25 bay front intake fan, cutting out the rear grill, leaving off the rear slot covers and even removing the rear slot pillars. On my case I have six filtered intake fans (all under 1000 rpm) and zero exhaust fans. Air just leaves the case quietly.
 

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Negative pressure can also cause stagnation. Positive pressure can direct the air where it needs to go where as negative pressure can not. Positive pressure doesn't by itself cause stagnation or impair cooling. The lack of air FLOW does however. Without positive air flow you'd have total stagnation.

If your case doesn't draw in dust around the small openings, then you have positive or neutral case pressure, not negative case pressure.

There should not be any need for six fans. Two or three is usually plenty. Do you have a fan fetish?
wink.gif
 

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Originally Posted by AMD4ME View Post

Negative pressure can also cause stagnation. Positive pressure can direct the air where it needs to go where as negative pressure can not. Positive pressure doesn't by itself cause stagnation or impair cooling. The lack of air FLOW does however. Without positive air flow you'd have total stagnation.
If your case doesn't draw in dust around the small openings, then you have positive or neutral case pressure, not negative case pressure.
There should not be any need for six fans. Two or three is usually plenty. Do you have a fan fetish?
wink.gif
honestly who doesnt
 

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I knew there were people with fan fetishes but I've never met them personally...

Have you considered FFF - Frightful Friends of Fans ? They have a 200 step treatment program.
biggrin.gif
 

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Discussion Starter · #19 ·
Quote:
Originally Posted by Houston View Post

How do you know if your case is high or low pressure? Also, how does one go about having a higher pressure case?
There are a few fan manufacturers (Silverstone comes to mind) who make fans that are specifically designed to promote the static pressure within a chassis. This is usually measured in mmH2O and is analogous to the ability for enthusiasts to increase the positive airflow within their enclosure more effectively.

Silverstone makes a couple versions of their Air Penetrator fans in different sizes, including 120mm, 140mm and 180mm (AP121, AP141 and AP181 respectively). Here's a YouTube video of the AP121 fan at work versus "regular" fans:
.
 

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Higher static fan pressure may or may not result in a positive case pressure differential to atmosphere. The increase static pressure means the fan is capable of pushing the air harder. These fans may be useful if there is significant flow resistance. If however the exhaust fans are pulling more air than the inlet fan is pushing, the case can still be negative in pressure. There are many possible configurations and possibilites.

If you have a really open case like "ehume" with almost no flow resistance out the back, normal inlet fans may still be able to produce a neutral or slightly positive pressure - depending on their flow capability. The only way you could tell what is happening is with accurate differential pressure testing inside the case or by following the dust trails.
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