More powerful fans pushing air in or pulling out? (Positive v. negative pressure)

[Hender]

I have an Antec SX1030 (the most popular case in the world, at least last year when I got it) case, and I'm trying to find the most efficient way to cool it without actually modding the case. No drilling holes, no cutting fans slots, nothing. It has two 80mm front fan holders and two rear, and right now I have all four filled with sub-30 dBa fans to keep the noise down a bit, but I'm switching them around with a couple new ones to raise the volume a bit but increase circulation. Now, should I have the more powerful fans blowing air in or sucking out? I have the front fans pulling air into the case since that seems more logical. Fans in the rear sucking air in would hit the CPU first, but the recycled air from the power supply would be in just the right place to get pulled back in, not to mention the fact that my computer is under a desk and wouldn't get fresh air. OK, so positioning is set. Pulling air in the front, pushing in the back.

So that brings me back to my original question, more powerful pulling in or pushing out? The more powerful fans pulling air in has an advantage of pulling cool(er) air into my case for the CPU fan to use in cooling the heatsink, but likewise, if the rear fans aren't very good at pushing air out, the hot air coming off the heatsink could just get recycled and used again.

Any thoughts? Or am I just rambling?

 

[PCHPlayer]

IMHO
Positive pressure: With filtering can eliminate dust in the case. Could reduce airflow through the case.
Negative pressure: With filtering can significantly reduce dust in the case. Dust can still get in through small openings in case (including CD Drives and floppies). Better airflow through the case (Assumes intake in front and exhaust in rear).

If I were you I would just install fans in all 4 case brackets and add filters to the front of the case.

 

[WangButter]

Positive pressure (with filtering of the intake fans) is better to keep dust out of your case, however, it means that more hot air will be circulating inside your case waiting to get out, so it's worse for cooling.

Negative pressure is better for cooling, because the hot air will get exhausted from the case quicker, and there will be less pockets of "dead air" stuck inside the case.

IMO, it's best to keep your air pressure as neutral as possible, but slightly on the negative side.

 

[Buz2b]

IMO, it's best to keep your air pressure as neutral as possible, but slightly on the negative side.

Just to confuse you a bit more , I believe the opposite. I think you should keep it slightly on the positive side to keep out dust and assure influx of fresh air. If it still has decent exhaust, the warm air will eventually get removed and not sit in the case too long. Negative condition just means more dust from cracks and assorted holes in the case that will reduce cooling efficiency fairly rapidly. Just up the cfm fans in the front (intake) about 20% -30% above the ones in back. You need a bit more from them anyway because their source is blocked a bit by the front of the case.

 

[FenrisUlf]

Personally, I think filtering with slightly positive pressure is the way to go. I have a case that I've run with slightly negative pressure for several years and have gone through two CD drives due to dust contamination. Postive pressure will push the air out just as effectively as negative pressure will pull it in. Technically, the higher pressure will cause a slightly higher density of air which will allow more heat to be taken from the hot components, but in reality this will be an imperceptable difference. What is more important is to make sure that wires and cables don't block the airflow. Plus, your power supply has an exit fan, don't forget to take this into account. It has become fairly standard for air to be sucked in the bottom front and exited in the top back for a reason - it works.

 

[zephyrprime]

the higher pressure will cause a slightly higher density of air which will allow more heat to be taken from the hot components

This is true but remember that presurizing gases increases the temperature of the gas. But like you said, this will add up to next to nothing.

Does anyone know the actual answer to this question? Has anyone actually tried every combination of fan arrangements and took measurements.

 

[risgool]

Check out this article on Tweakers : Link

 

[Buz2b]

Check out this article on Tweakers

First of all risgool, thanks for pointing out the article. It is an interesting article and pretty well written. However, a bit confusing. He talks about the best case scenario (pardon the pun) as being "underpressure", aka negative air flow but in his conclusion and final recommendation he has more intake vs exhaust; which would cause, in his words, overpressure--positive air flow. He also stated that using a top exhaust "blowhole" does not reduce the hot air in a case. Excuse me?? Basic, and I mean basic science tells you that hot air rises. The hottest air in a case will be right at the top behind the PS, optical drives and hard drives, depending on your arrangement. I think it is important to remember one thing though; this author is one person who is able to express his opinion on a website. We do not know his credentials, experience or qualifications for doing so. In actuality, we are the same and doing the same right here. No better, no worse. So add his opinion to the list of many who have expressed theirs; including mine. Personally, and IMHO, I do not want "underpressure" or negative airflow in my case, which would cause unfiltered air to be sucked in from various nooks and crannies of my case. It would be unfiltered and only add to the "dust bunnies" that cause overheating; not to mention inefficient and insufficient to provide optimal cooling. Perhaps, and if someone had the time and inclination to do so it would be interesting, the "underpressure" or negative air flow might work if you were able to effectively seal off ALL possible "leaks" that exist in your case. That would mean around all the bezels, the entire front of the case, etc. In that case, you might cause that "wind tunnel" effect he was hoping for; possibly. In that scenario, if the only air that could enter the case could be filtered and concentrated and the outgoing rate was significantly higher than the intake, you would effectively remove the hot air almost immediately; replacing it with a steady supply of cooler, filtered air. Maybe.........

 

[tazdevl]

Also depends on the fans you're using, size of your case etc... bottom line is that there is no pat answer. You have to play with it. I've got a PC60 and this case, with my components, does best with negative pressure. I've tried positive and pretty much equalized airflow.... negative works best.

 

[SNoWyV82]

Okay, I've got a Lian Li. I achieve negative air pressure by having more fans intaking air than those exhausting it right? What is the stock configuration of the PC60 (how many are blowing in/out)? Thanks.

 

[Buz2b]

I achieve negative air pressure by having more fans intaking air than those exhausting it right?

Sorry, no. Negative pressure is when you have more cfm of air being exhausted by fans than there is for Intake.

 

[SNoWyV82]

Good, that makes life easier. That is how my case will be set up stock. Thanks.