The age-old dust question...

Phosphonothioic · Sep 24, 2013

Could some of the experts out there impart some wisdom to me about minimizing the accumulation of dust in your system?

I have a Fractal Arc Mini and the filters do a heck of a good job, but I do have to clean them often. Is there anything to be said about the positive vs. negative case pressure here, or am I mixing up my concepts?

The articles I'm finding on line are mostly saying "Slap a filter on" which is the 'DUH' thing to do. I'm just curious if there is anything else, even if it's small, that I could be doing.

Thanks.

Sakkura · Sep 24, 2013

Positive pressure leads to less dust accumulation than negative pressure. All the holes in the case (where the fans aren't blowing) will either let air in or out. Whether they let air in or out depends on the pressure inside the case vs. the pressure outside. Negative pressure means the pressure is lower inside, so air will flow in. And when air flows in, dust will follow.

Phosphonothioic · Sep 24, 2013

Sakkura :

Does running a positive pressure result in higher case temperatures? I'm assuming positive pressure happens when you have more fans pushing out than in, correct? (duh...)

InvalidError · Sep 24, 2013

Positive pressure is the only way to mitigate dust inside your system: you put your strongest fans behind an intake filter to catch most dust on its way in, use the fewest exhaust fans possible to avoid driving negative pressure and the slight positive pressure this generates prevents dust from entering through other case openings.

With a negative pressure build, intake-exhaust balance goes to hell, case pressure goes negative and dust gets sucked in through every opening which renders intake filters largely ineffective.

Not much can be done about the filter cleaning... either slap an extra filter in front of the existing filters or slap filters in front of extra intake fans. More filters to wash but they will clog up a little more slowly.

Deemo13 · Sep 24, 2013

What I did on my computer quite a long time ago was take those nylon things you find in the store (you know, the things women put on their feet to try shoes on) and put those on my intake and exhaust fans. They were hard to clean, but they kept the dust out while minimizing airflow reduction.

Now, I just use a canister of compressed air, got lazy.

Sakkura · Sep 24, 2013

Phosphonothioic :

Not really. Theoretically, the best balance of high cooling performance and low noise is achieved by balancing intake and exhaust fans, for a neutral pressure configuration. But a small positive (or negative) pressure shouldn't make much of a difference.

InvalidError · Sep 24, 2013

Phosphonothioic :

There is no reason for positive pressure to cause higher temperature as long as the flow is "structured" properly. If you take the example of a GPU with blower style fan with rear exhaust, the positive pressure inside the case would help shove the GPU's hot air out the rear GPU vent which should help lower temperatures.

You got positive pressure backwards. Positive pressure happens when you try to bring more air in than what can get out without pressure increase. For a positive pressure build, you would configure just about every filterable fan except the rear CPU area exhaust for intake.

Phosphonothioic · Sep 24, 2013

InvalidError :

In my Arc Mini, at the moment, I have two 120s on intake a three 120s on exhaust...

Could you look at the case and make a suggestion on the setup?
Arc Mini

There are two front fans, two top fans, one side fan and one back. The side is out of commission due to my cooler.

Is it as easy as CFM-in > CFM-out?

Sakkura · Sep 24, 2013

InvalidError :

You shouldn't overdo it like that. The main purpose of case fans is still moving air through the case - not fighting to create as high pressure as possible within a leaky structure (a pretty futile struggle).

Sakkura · Sep 24, 2013

Phosphonothioic :

AFAIK there is a 120mm fan mount in the bottom of that case. If the power supply doesn't cover it, you can simply move one of the exhaust fans down there, giving you 3 intake and 2 exhaust fans.

InvalidError · Sep 24, 2013

Sakkura :

Lets go through this then...
1- side fan: as exhaust, all it does is dump fresh air from the front outside and make the GPU fan work harder to blow hot air out the back. Better off as intake.
2- top fan, front position: there are no heat-dissipating components in the path between the front intake and this fan position, which makes it useless as exhaust unless used to mount a radiator, not particularly useful as exhaust otherwise so better off as intake or unused.
3- top fan, rear position: depending on exactly how things line up inside the case, this fan position may rob fresh airflow from ever going across the HSF or other hot components, so not particularly useful as exhaust unless using a radiator, better off unused if going for positive
4- rear exhaust: this is the only absolutely essential exhaust fan

Keep in mind that filtered fans lose a large chunk of their airflow capacity from having to hold static pressure to pull air through those filters. Having multiple exhaust fans (which are unhindered by filters) will quickly switch the case to negative pressure so you need 2-3 filtered intake fans per exhaust fan to balance that out.

Phosphonothioic · Sep 24, 2013

InvalidError :

Sakkura :

Lets go through this then...
1- side fan: as exhaust, all it does is dump fresh air from the front outside and make the GPU fan work harder to blow hot air out the back. Better off as intake.
2- top fan, front position: there are no heat-dissipating components in the path between the front intake and this fan position, which makes it useless as exhaust unless used to mount a radiator, not particularly useful as exhaust otherwise so better off as intake or unused.
3- top fan, rear position: depending on exactly how things line up inside the case, this fan position may rob fresh airflow from ever going across the HSF or other hot components, so not particularly useful as exhaust unless using a radiator, better off unused if going for positive
4- rear exhaust: this is the only absolutely essential exhaust fan

Keep in mind that filtered fans lose a large chunk of their airflow capacity from having to hold static pressure to pull air through those filters. Having multiple exhaust fans (which are unhindered by filters) will quickly switch the case to negative pressure so you need 2-3 filtered intake fans per exhaust fan to balance that out.

I like to think of myself as an educated man...but I certainly brain-farted on this one. I'll have to open up my case and clip some zip-ties tonight so I can reconfigure my fans. This pretty much spelled it out for me. Thanks.

teddymines · Sep 24, 2013

Regarding the PSU, I have mine (Corsair TX650) with the intake fan facing the components. The PSU fan rarely runs as it is. With positive case pressure, it seems logical that some air will escape through the PSU and out the back.

As far as dust that does eventually get in there, twice a year I simply take my case out to the garage and blow it out with compressed air. It also helps to not have it running 24/7 unless you need to.

Sakkura · Sep 24, 2013

InvalidError :

1. Didn't he say that spot was blocked?
2. So?
3. What? That's directly above the VRMs and the CPU cooler. It's also above the graphics card. Hot air rises, so this is the ideal spot for an exhaust fan.
4. If the CPU cooler expels air towards it, it's a good position for an exhaust fan. If the CPU cooler expels air upwards, it's not a particularly good position for an exhaust fan.

The best solution here is two intake fans in the front, one in the bottom, and presumably one in the top rear and one in the upper rear, though it depends on the CPU cooler.

Phosphonothioic · Sep 24, 2013

teddymines :

I put mine to sleep whenever I step away for extended periods. And I, too, give it occasional 'baths' a couple times a year.

Phosphonothioic · Sep 24, 2013

Sakkura :

InvalidError :

1. Didn't he say that spot was blocked?
2. So?
3. What? That's directly above the VRMs and the CPU cooler. It's also above the graphics card. Hot air rises, so this is the ideal spot for an exhaust fan.
4. If the CPU cooler expels air towards it, it's a good position for an exhaust fan. If the CPU cooler expels air upwards, it's not a particularly good position for an exhaust fan.

The best solution here is two intake fans in the front, one in the bottom, and presumably one in the top rear and one in the upper rear, though it depends on the CPU cooler.

I have a Hyper EVO 212 push-pull pointing towards my rear exhaust. I'll scope out the bottom fan tonight, I think there's a slot for it, in which case, I'll move the top rear down as an intake.

InvalidError · Sep 24, 2013

Sakkura :

The rear fan still draws air across the VRM, CPU and GPU "top" area regardless of HSF orientation. If the case has slight positive pressure, that pressure will also shove any rising hot air out through the top vents even without fans.

The big problem with 140mm top fans is they pull enough air to easily overwhelm 3-5 filtered 120mm fans and if the main objective is dust mitigation, operating those 120mm fans at high speeds is not a good idea since this will suck a lot more dust through the filters.

Sakkura · Sep 24, 2013

InvalidError :

Sakkura :

The rear fan still draws air across the VRM, CPU and GPU "top" area regardless of HSF orientation. If the case has slight positive pressure, that pressure will also shove any rising hot air out through the top vents even without fans.

The big problem with 140mm top fans is they pull enough air to easily overwhelm 3-5 filtered 120mm fans and if the main objective is dust mitigation, operating those 120mm fans at high speeds is not a good idea since this will suck a lot more dust through the filters.

So now the fans in the top are suddenly 140mm instead of 120mm? Where did that come from?

InvalidError · Sep 24, 2013

Sakkura :

I looked at a photograph and it looked like 140mm fans would fit in there but you are right, those are 120mm.

In any case, one unhindered 120mm fan still shifts a lot more air than an identical fan with a ~200 microns filter on it.

Sakkura · Sep 24, 2013

Well the exhaust fans aren't entirely unhindered either. And fan filters aren't that bad as long as you keep them reasonably clean.

Anyway, having 3 intake fans (2 front, 1 bottom) and 2 exhaust fans (top rear, upper rear) is the optimal configuration here. Putting an intake fan at the top of the case is a terrible idea.

If it's really necessary, you can run the exhaust fans a little bit slower.

InvalidError · Sep 24, 2013

Sakkura :

Only way to know for sure would be to see what an FLIR camera would have to say about it.

The age-old dust question...

Distinguished

Illustrious

Distinguished

Titan

Splendid

Illustrious

Titan

Distinguished

Illustrious

Illustrious

Titan

Distinguished

Distinguished

Illustrious

Distinguished

Distinguished

Titan

Illustrious

Titan

Illustrious

Titan

Share this page