Air Flow

[rbp45]

Which air flow is more efficient cooling and power saving for desktop PC case ?

Maximum inlet air to case eg. 3 inlet fan & 2 exhaust fan
or
Maximum out-let air from case eg. 3 exhaust fan with single inlet fan.

 

[Blain]

You can't get enough positive air pressure in a standard case with regular fans to make any difference.
Best efficiency and cooling would come from intake and exhaust being equal.

 

[OptimumSlinky]

Pardon the slight hijack, but I am looking to add side fans to my case and had a question regarding air flow. Presently, my case has a 120mm fan at the front (intake), and then the Corsair H50 exhausting out the back under the PSU. The case has two pre-made vents/slots for two 120mm side fans.

Will filling both slots with intake fans disrupt air flow greatly? The majority of my heat seems to be coming from my Radeon HD 5850 (placing a hand next to the currently empty vent results in noticeable heat coming off the card). I had originally thought about setting the side fan as an exhaust like in the new Xbox 360 design, but my understanding is that will disrupt proper intake-exhaust flow from front to rear. So now I'm thinking about 120mm at the front (intake), two 120mm fans on the sides (intake), and then the single 120mm exhaust out the back. Does this make sense?

 

[joelmartinez]

I prefer positive air pressure because it means less dust, i currently have 3 intakes and 1 exhaust soon to be 5 intake 0 exhaust it really isn't pressure that matters but flow. if you run 0 exhaust (have done that before just not doing it currently) make sure to have push/pull on an east/west heatsink to push air out the back grill (which you should cut off btw)

 

[JBDan]

This is quite old (almost 8 years!), but I have found very similar results in all the airflow tests I have done. click here

 

[kamikazekyle]

I actually did some testing with this, and a lot of factors come into play. I have an Antech 900, for the record, along with all low-speed Yate Loons and the stock 200mm top fan. That means 2 front intake, 1 side fan (this is temporarily a OMG low speed Coolmaster since I broke the Yate that was there), 1 rear exhaust fan, plus the top exhaust fan.

I found -- with video cards that vent mostly inside the case -- most temps were within 1*C difference on both video card and CPU so long as I kept the two front fans on intake. All other fans exhausting, all other fans intake, all other fans mixed...didn't matter. *BUT*, when I changed to a different video card -- also venting inside the case -- by flipping the side fan to exhaust I actually decreased the card temperature by 2-3*C. The video card was venting inside the case but the side fan was directly located next to the vents on the video card. By directly sucking out a lot of this hot air, it helped.

Moral of the story: get a sheet of paper, a good thermal benchmark, and try different configs. Different cases can lead to different needs as well.

After seeing that artical JBDan mentioned, I might have to try my test again with the front fans disabled. It doesn't seem to make sense with no fresh air being actively vented into the case, but hey, who knows

@OptimumSlinky: See above. I noticed a drop when I switched my side fan to exhaust, but the location might be pretty key. If it's too far down it might acutally interrupt the video card cooler's ability to pull in cooler air. In that case you migth want it to vent inward.

 

[Sunny129]

After seeing that artical JBDan mentioned, I might have to try my test again with the front fans disabled. It doesn't seem to make sense with no fresh air being actively vented into the case, but hey, who knows

that's b/c fresh air IS being brought into the case, despite the absence of intake fans. just b/c there are no intake fans actively drawing fresh air into the case doesn't mean that fresh air isn't passively being drawn into the case. in fact, its being passively drawn into the case by the exhaust fans themselves. the hot air being drawn out of the case by exhaust fans must be replaced by more air, or else the inside of your case would become a perfect vacuum with no air inside it (which is impossible given that cases aren't air tight). hence fresh air will still replace the hot air that gets exhausted even with exhaust fans only (assuming you don't have a GPU that exhausts more hot air into the case than the exhaust fans are capable of exhausting)...and folks will generally see lower temps than they actually expected to see.

now this isn't to say that adding an intake fan or two won't help improve airflow inside the case, but just as an "exhaust fans only" setup is better than a setup with no fans at all, some semblance of airflow inside the case is better than no airflow at all...and an "exhaust fan only" setup will of course provide more airflow than one with no fans at all.

 

[kamikazekyle]

that's b/c fresh air IS being brought into the case, despite the absence of intake fans. just b/c there are no intake fans actively drawing fresh air into the case doesn't mean that fresh air isn't passively being drawn into the case. in fact, its being passively drawn into the case by the exhaust fans themselves. the hot air being drawn out of the case by exhaust fans must be replaced by more air, or else the inside of your case would become a perfect vacuum with no air inside it (which is impossible given that cases aren't air tight). hence fresh air will still replace the hot air that gets exhausted even with exhaust fans only (assuming you don't have a GPU that exhausts more hot air into the case than the exhaust fans are capable of exhausting)...and folks will generally see lower temps than they actually expected to see.

now this isn't to say that adding an intake fan or two won't help improve airflow inside the case, but just as an "exhaust fans only" setup is better than a setup with no fans at all, some semblance of airflow inside the case is better than no airflow at all...and an "exhaust fan only" setup will of course provide more airflow than one with no fans at all.

Uh, duh? That's why I mentioned ACTIVE intake. I know that air is still being drawn into the case with exhast fans. I had assumed others would know this as well, so I didn't feel the need to iterate the point.

I never mentioned that NO air was being drawn into the case with exhaust only. The odditiy I found is in the fact that having no ACTIVE flow into the case results in lower temps. Nor did I make mention of having no fans in the case.

This is dependent on the case/case layout, existing fans, and existing hardware. If you have enough air being moved throught the case and over key components -- exhaust only, intake only, or via voodoo-- you're going to achieve cooling.

As I tested last night -- in my Antec 900 with a side 120mm exhaust and a rear top 120mm exhaust only -- temperatures were several degress higher over a span of only 5 minutes vice with two 120mm intake fans adding active flow. This indicates that an exhaust only configuration in my case was not sufficent CFM draw over key components in order to keep heat down. Perhaps if I had more exhaust or more open vents or more strategically placed fans I could achieve an exhaust only setup.

So, my addage still stands: test what you have.

 

[Sunny129]

Uh, duh? That's why I mentioned ACTIVE intake. I know that air is still being drawn into the case with exhast fans. I had assumed others would know this as well, so I didn't feel the need to iterate the point.

I never mentioned that NO air was being drawn into the case with exhaust only. The odditiy I found is in the fact that having no ACTIVE flow into the case results in lower temps. Nor did I make mention of having no fans in the case.

sorry for the misunderstanding...