negative or positive case pressure

[Burning Phoenix]

what do you think? My reason for asking is after all these past months i found my setup was a bad design. I figured i'd place many exhaust fans(4) and a single intake at the front bottom. I thought the pure power of the 4 exhaust would pull an equal amount of forced intake air inward. But guess what WRONG! Today my computer had been running for months without shutdowns and as posted in GD i had a same problem. Anyways I cleaned my intake filters ; meanwhile the computer is running ; and after reinstalling them i noticed the drop in temperatures on MBM. I had a drop of 4C+ on both the motherboard and CPU while i was rinsing the air cleaners. Well I can only assume now i'm going to haveto try forcing more air instead! What do you think?

EDIT : that me say at this time of writing this post my temps ; which i watch in Fahrenheit ; are 91F CPU and 73F motherboard. They used to be 98F and 80F respectively. This is within 30 minutes or less.

ANother EDIT 3 hours later: down to 86F and 69F doing my usual work on this computer.

[Staz]

Definately positive pressure.

More air blowing in than out. Otherwise you get dust in the Floppy, CD rom, And any other small opening.

[Diggrr]

I'll ring in with my vote here...slightly positive pressure.
You want alot of cool air coming in, but you don't want it too restricted when it's trying to leave with the heat. That will slow down the cooler air coming in.
As an example, Hoot had a great positive airflow setup, but made more improvements in making sure all that air could get out too.

Just my $.02 worth.

[Burning Phoenix]

i can't believe all this time i could of dropped so much more temps by using fans the right way.
I'm currently running seti; like i always do this time of night into the next evening; and my temps are staying down 7C from where it usually maxes at.

ambient: 62F (16.6C)
full load: 111F (43.8C)
idling: 86F (30C)

[Jeniva]

I'd go with the Positiva pressure thing....I just added another 120mm fan to my case,,now its slightly positive...

[TruckChase!]

Besides just being easier to manage flow, positive pressure would have the ability to absorb more heat due to the fact that it's more dense, however, I doubt that that would come into play with this low variance in pressure anyhow.

So now that I talked in circles, I guess I have to say positive. :)

[Greedy Guido]

Burning Phoenix,

You must remember that axial flow fans do not like to suck (not to say that they are not used for this purpose). They perform much better if the suction is unrestricted and are allow to blow. ID fans are one of the few fans designed to suck but they also have limitations.

[docJ]

Lets remeber that its the volume of air and where it goes that counts. If the case has a positive pressure then the exhaust fan(s) are limiting the air flow. If you have a negative pressure then the intake fan(s) are limiting the air flow. Filters also limit air flow, but not only do you need good air flow, you need it to go to the right places, not so easy. This is why ducting works well. The small increase in pressure that these case fans have, will not make enough difference in the air density to cause the air to cool any better. I think its better to work on good air flow and getting it to the places that need cooling.

[rogerdugans]

All my systems seem to get the best results with a very slightly negative pressure: example- this on has one 92mm intake, a ducted cpu intake (60mm 4500 rpm) and 2 80mm exhausts plus the psu fan. To control the airflow in this mini tower case I have two 80mm at 7v fans inside redirecting flow. It is a mini-tower so it is cooling challenged! I'm getting 32c mobo temp and 40c cpu, with case temp (indoor/outdoor thermometer) of 72f and ambient of 71f.

I do have to clean fans and heatsink every few months; positive ventilation isn't bothered as much by fan filters- helps keep dust out- and air won't be getting sucked in through all the cracks and crevices in the case, helping even more.

Its up to individual systems, but either way, a fairly close balance is best.
NOTE: Fan filters place extra restriction on the intake, and while I never did do the experiment, what I did do leads me to believe that an EXTRA 80mm intake (on top of the slightly positive balance) would keep intake volume up with filters on all the intake fans....Shoulda tried it though

[Wa11y]

Well, I have very little experience with air pressure, since I usually leave my case panels off, but since I recently got a Swifty MCX462, I want to put the walls on the deaden some sound, so this has become of particular interest to me.

I recently added an intake fan to power supply. It moved more CFM than the stock exhaust fan on the power supply, causing positive pressure in the power supply. I noticed that the power supply was getting physically hot to the touch, and radiating heat. Not hot enough to burn, but noticably warmer than ambient. This was with the case panels off, in an unfinished basement in winter. I swapped the exhaust fan with the same type and brand as the intake, and fired it up. Lo and behold, the power supply stays about ambient. It's not getting near as warm as it did with the two different fans.

Again, this is pretty much my only experience with positive pressure, but from what I personally have experienced, I'm thinking either even pressure, or negative pressure.

[docJ]

Clean air is good for man and machine. I do admit that a slight positive pressure (with filters) will help keep the dust and stuff off the hs. From a cooling point higher pressure will not change things. However it may change your flow paterns inside your case and this may be where increased cooling comes from. Lots of clean air is good no matter how you do it.

[UserName]

Really the correct answer is zero. All fans get max airflow at zero delta air pressure. But that's just being silly. Since fans are more efficient at blowing the should blow. Reconize that a fan removing air from a positive presure is much more efficient than the fans that are pressurizing that area.

Realy tho a case pressure of zero would mean max air flow.