FEATURED Positive case pressure vs Negative case pressure

Automata · Feb 13, 2009

Since there was a heated discussion in another thread regarding whether positive case pressure is better or worse than negative case pressure, I decided to create a thread and poll so that can discuss and see what everyone has.

KEEP IT CIVIL

Not only do we want to see what people are using, we want to see the reasons behind it. Discuss.

CGR · Feb 13, 2009

I try to keep slightly positive case pressure to keep dust/cat fur out of my case.

=XAF=AfterShock · Feb 13, 2009

I have 4 120mm fans in my case and I've played around with push/pull and having all blowing in or all blowing out but the best results I got were having the front/side/rear blowing in then the having the top exhaust and power supply fans blowing out, the pressure is high enough to where I can unplug the top 120mm and it will continue to spin at a pretty good speed but I was getting lots of dust and cat hair build up so I made some filters out of the same material nylons are made of but it's clear and has very little air restrictions compared to regular fan filters

ticktock123 · Feb 13, 2009

This is a really good question. I would like to see any science behind it. Right now i have my case side off (yeah i suck at cooling) but i would think that a (-) air presure would have more movement of the air INSIDE the case. (+) i would think would keep it all in the same area and produce hot spots.

Rick James · Feb 13, 2009

I'm doing alittle experiment. I have placed a temp sensor inside the computer case and we'll see how efficient my fan setup is. I'll give it an hour and we'll see how well my case cools compared to ambient.

antipesto93 · Feb 13, 2009

i have heard people say positive is always better,
but i would have thought negative was better, as the aim is to get all the hot air out of your case right? and air is always going to come from outside the case ( mesh/holes/cracks )..but if course some positive fans would help.......hmm actually i think its a never ending argument !

JLK03F150 · Feb 13, 2009

I have two 120mm side intake fans and one 120mm rear exhaust & the PSU fan is an exhaust too. The three fans are high CFM & it's quite pressurized. My "system temp' usually stays in the high 20Cs to low 30Cs.

I have a first generation Antec Sonata mid-tower case. I replaced the rear fan & added the two side panel fans.

muddocktor · Feb 13, 2009

I try to keep a slightly positive pressure in my case. That way dust doesn't get sucked into the optical drives. But I don't think it makes a big difference if you are just slightly positive or slightly negative in most case designs.

Rick James · Feb 13, 2009

An hour and a half into the experiment.

Ambient : 66 degrees F
Inside the Case : 75 Degrees F

Dermen · Feb 13, 2009

I thought negative gave slightly better temps but positive ensured that all air went through the intake fans, which leads to less dust/hair/crap if the intakes are filtered.

I have slight positive pressure, 4x120mm filtered intakes, 3x120mm + 1x80x10mm exhaust.

downer · Feb 13, 2009

I have a positive pressure. I've always had more fans dedicated to intake than exhaust. No science behind it for me, it just seemed to make sense to do it that way.

3 x 120mm fans on my triple radiator suck air into the case, through the rad

2 x 120mm case intake fans

1 x 120mm Exhaust

1 x 120mm Exhaust on the PSU

nd4spdbh2 · Feb 13, 2009

negative pressure in all my cases here.

Main rig on the upper section, has a 120mm yate in, and 2 120mm yates out... bottom section is about even 1 120mm in 1 out

Server is completely negative. Taped off all the intakes besides the ones i want air coming in and have a 120mm antec tri cool at 5v medium on the switch out the back, and a 80mm psu fan thats slow.

I like running negative because you can predict the airflow and dont get hot spots / weird etties. (theres a reason why most dell desktops are all negative case pressure)

MVC · Feb 13, 2009

I do negative pressure on all my cases. As mentioned above, it does create a dust problem since the case is sucking in air from every crevice but it also ensures that air is flowing through the case, not just being pushed into it. Keep in mind, it isn't a whole lot of negative pressure, just enough to ensure a "draft" inside the case.

In my situation I need to clean out the dust buildup about every 3 months, which I find acceptable. If I was in an environment that would require me to clean out the dust buildup every week I probably wouldn't find it acceptable and I'd be using positive pressure to keep the dust buildup down. It's all relative.

But, if you're looking for maximum cooling you'll need to go negative pressure since that will get you the maximum airflow through the case.

Automata · Feb 13, 2009

Either of you mind explaining how negative pressure moves more air? Been thinking about it for awhile and I don't grasp that concept.

MVC · Feb 13, 2009

thideras said:
Either of you mind explaining how negative pressure moves more air? Been thinking about it for awhile and I don't grasp that concept.

The simple answer is that it doesn't. If the sole exhaust fan is a 1200 RPM 80mm the amount of air it can exhaust is the amount of air it can move. Period.

However, with positive pressure the air the exhaust fan(s) will move is the air it has easiest access to. Air in the corners, crevices, under the video card, &c will become pockets of stability where the air doesn't move because other air can be pulled into the exhaust easier. The air in these pockets gets heated by the nearby components and stays that way since it isn't being circulated and exhausted.

With negative pressure those pockets of stability disappear. The exhaust is working harder than the intake, basically creating a vacuum inside the case, so those pockets of stability can't form. And that in turn ensures that all the air in the case is being circulated and heat doesn't build up around any single component--heat source.

There are, of course, other ways to ensure that pockets of stability don't form where you really don't want them (see for example Lian Li's side intake just under the video card on their newer cases), but as a general principle and without going to additional effort, negative pressure will provide a cooler case interior.

The optimum configuration can be different in every situation. If the only real pocket of stability is in the top front of your case and there aren't any components there (heat rises so it will try to go up an since the PSU is generally toward the back the top front is a place heat collects) you might choose to ignore it. I would. If, however, the overpressure from a positive pressure system is creating a pocket of stagnant air around the hard drives and they're running warmer than they would with proper circulation I'd work on eliminating that pocket of stability and negative pressure is the first thing I'd try. It's all a question of tuning--there is no "right" answer that always applies.

If I haven't explained this well enough, i.e, you have questions, please ask for clarification.

Marco

WonderingSoul · Feb 13, 2009

I rely more on air movement than pressure. If you have good movement of the air with few dead spots, no matter how you slice it (positive or negative) it should be fine.

I do however, have positive air flow in my rigs. One right now has three low speed Yates and two 80mm intakes and only two 80mm exhaust + psu 80mm. I couldn't be happier with the results.

MVC · Feb 13, 2009

WonderingSoul said:
I rely more on air movement than pressure. If you have good movement of the air with few dead spots, no matter how you slice it (positive or negative) it should be fine.

Agreed! As long as the dead spots (pockets of stability) are in areas that aren't critical. I once had a pocket form just behind the hard drives in Antec case (a Sonata I think) and the south bridge was running a lot hotter than it should have been. I ended up increasing the intake and the exhaust to get the temps to where I wanted them, and then I ended up selling the case to move on to other things.

WonderingSoul said:
I do however, have positive air flow in my rigs. One right now has three low speed Yates and two 80mm intakes and only two 80mm exhaust + psu 80mm. I couldn't be happier with the results.

Like I said, it's a question of tuning. If it ain't broke, don't fix it. But, if it is broke, simple, inexpensive changes can have a significant effect.

DarkFury · Feb 13, 2009

Rick James said:
An hour and a half into the experiment.

Ambient : 66 degrees F
Inside the Case : 75 Degrees F

upgrade some of your fans =p , but yea coolermaster is a great case for air flow

my haf stays within 4 degrees F from ambient. on 100% fan load though :thup:

mbigna · Feb 13, 2009

Ideally, one would want neutral pressure (just as much air being sucked in as there is being blown out). As far as how it affects your drives with doors (optical, floppy, zip, whatever...) if dust can be sucked in through the door, dust can be blown out the same way--so unless you are filtering intake air, it doesn't make a difference.

Whether there is positive or negative pressure inside the case as compared to outside insn't as important as how much air FLOW you have going through the case. Just like a water block, you want to have a lot of flow and a lot of turbulence so no hot spots (areas where the same air is caught in a stable vortex) are created.

Neuromancer · Feb 13, 2009

MVC said:
The simple answer is that it doesn't. If the sole exhaust fan is a 1200 RPM 80mm the amount of air it can exhaust is the amount of air it can move. Period.

However, with positive pressure the air the exhaust fan(s) will move is the air it has easiest access to. Air in the corners, crevices, under the video card, &c will become pockets of stability where the air doesn't move because other air can be pulled into the exhaust easier. The air in these pockets gets heated by the nearby components and stays that way since it isn't being circulated and exhausted.

With negative pressure those pockets of stability disappear. The exhaust is working harder than the intake, basically creating a vacuum inside the case, so those pockets of stability can't form. And that in turn ensures that all the air in the case is being circulated and heat doesn't build up around any single component--heat source.

There are, of course, other ways to ensure that pockets of stability don't form where you really don't want them (see for example Lian Li's side intake just under the video card on their newer cases), but as a general principle and without going to additional effort, negative pressure will provide a cooler case interior.

The optimum configuration can be different in every situation. If the only real pocket of stability is in the top front of your case and there aren't any components there (heat rises so it will try to go up an since the PSU is generally toward the back the top front is a place heat collects) you might choose to ignore it. I would. If, however, the overpressure from a positive pressure system is creating a pocket of stagnant air around the hard drives and they're running warmer than they would with proper circulation I'd work on eliminating that pocket of stability and negative pressure is the first thing I'd try. It's all a question of tuning--there is no "right" answer that always applies.

If I haven't explained this well enough, i.e, you have questions, please ask for clarification.

Marco

Very eloquently put, wish I had your gift for language

As I said in the other thread, positive case pressure can work also if done correctly.

For instance... you have a fan blowing on your hard drives, and your entire side panel is intakes (4x120) blowing on all the hot components (a la the NZXT zero) you will think that positive case pressure does the ticket (has 2x120mm rear exhaust at the top by the CPU and the PSU in top and an 80mm in top to exhaust.

Positive case pressure. However they are low speed/low pressure fans so pressure is really a bad word for it...with enough grills and grate in the case, pressure probably does not even exist.

It probably has a dead spot at the very bottom of the motherboard, so tri or quad fire setups might over heat, and as mentioned top front of the case has no movement, nothing that would effect my setup.

I find that that case gets just as dusty and disgusting as my other negative case pressure systems, so not really sure how that argument holds up... (I suppose positive pressure with filters = less dust...)

For the record I voted peer pressure

FEATURED Positive case pressure vs Negative case pressure

Positive Pressure VS Negative Pressure

Positive Pressure

Negative Pressure

Peer Pressure

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