Fan orientation

[Foomanchu]

Haven't built a system in a long while and need some help here regarding the cpu fan orientation. I have a Gigabyte Aurora 3d case that includes 3 120mm fans. The front one is an intake and the back two are exhaust fans. I also have a PS that has a 120mm intake fan and an 80mm exhaust fan. I am using an Arctic Cooling Freezer 64 Pro cooler for the CPU that can be oriented to blow any way I see fit. This is where I can't make up my mind!

Should I: (A) Face the CPU fan towards the rear of the case, and push the air out of the 2 exhaust fans, or (B) Face the CPU fan towards the power supply intake fan (recommended by the PSU manufacturer).

Link to diagram


Thanks for your help!

 

[Luckyboy1]

I'm a big fan of positive case pressure. Some argue that the temps are lower when you lower the pressure. This may sometimes be true, but you will move less heat measured in BTU's which is what really counts. This is due to the fact in physics that says heat transfers better in a molecule dense environment. Lower the pressure and you lower the density of the air, reducing BTU transfer. If you've got three fans for the case, then you probalby have four when you count the power supply fan. So, for the case fans, two blowing in and one out.

In short, life in a PC should suck more than it blows!

 

[jonnyGURU]

Absolutely correct.

I think the negative pressure theory comes from the idea that air being brought into a chassis from multiple points of entry will cause tubulence that prevents the air from ever actually exiting. When in reality, it only takes one fan to direct that air out of the case. Even if that fan is just a PSU fan.

And don't forget, if you have too much negative pressure in the case, you create a vacuum and a sort of venturi effect with the PSU fan, robbing the PSU of the air it needs to cool itself! I've had to deal with quite a few people that assumed their PSU fans were mounted backwards when in fact it was the vacuum of the chassis defeating the power supply fan!

Your set up is very typical. What I've done in my case is made the fan in front spin at just under 2K RPM and the one in back at about 1200 RPM. You can't hear them at all, but you can definitely feel air coming out of the back of the power supply and case.

 

[Foomanchu]

OK, so I revised my awesome sketch which you can see by clicking HERE. Is this more along the lines of what you are recommending? Also, note that there is a mesh section above the PCI region on the case to allows air to escape (passively). Thanks guys, I appreciate the input!

 

[jonnyGURU]

No, no, no. I wouldn't do that. Now the PSU is the only exhaust.

Just make sure the fan in the front is bringing more CFM's in then the fan in the back. Any additional air will exhaust through the power supply.

 

[Foomanchu]

Gotcha! So I'll keep the original diagram, with option A, while making sure the front case fan provides more CFM. At least I think that's what you are getting at Thanks again!

 

[Operandi]

Originally posted by: Foomanchu
Gotcha! So I'll keep the original diagram, with option A, while making sure the front case fan provides more CFM. At least I think that's what you are getting at Thanks again!

Yes, that will probably be the most efficient fan configuration. The only down side is that it's not very good for noise, your front fans are by the most noticeable in terms of noise. Trying to make one intake fan keep up with two exhausts would surely result in quite a bit of noise.

A better solution would be to slow down the two exhausts to keep pace with the intake. That is if your are concerted about noise.

 

[iRONic]

Originally posted by: Foomanchu
Gotcha! So I'll keep the original diagram, with option A, while making sure the front case fan provides more CFM. At least I think that's what you are getting at Thanks again!

That's the way to go. Do you have a fan controller? It's an excellent way to keep the intake rpm's lower than the exhaust rpm's.

You can see my 3D Aurora setup here.

 

[LOUISSSSS]

omg did u just power an fx60 with an aspire psu lol

 

[MrX8503]

Is this a good fan orientation?

I havent seen a case like this, so i believe it would have to be made.

Also the dvd drive is facing you, in other words the drive will open on the side of the case. This would allow space for the fans.

http://i20.photobucket.com/albums/b225/...3/My%20Pictures/cpu_cooling_system.jpg

 

[iRONic]

Originally posted by: LOUISSSSS
omg did u just power an fx60 with an aspire psu lol

Why yes, yes I did. It's been running stable @2900 since the initial build without a burp.

Your point?

 

[HybridSquirrel]

this post reminds me of something. i have an 80mm case fan blowing in. and im gonna get a 120mm fan to suck in and i have a 120mm exhaust should i stick the side panel fan to blow out of the case instead of sucking in?

 

[Navid]

Originally posted by: Luckyboy1
This is due to the fact in physics that says heat transfers better in a molecule dense environment.

That may be true for conduction. Heat is transferred in this mode through the heat sink.

But, after heat is transferred to air, it moves only through the convection mode by the movement of air itself. So, really heat does not move through air. It is rather moved by the movement of the warm air.

The question is how much air you circulate through your case and what is the circulation path.

 

[Navid]

It is funny when someone compares a negative pressure computer case with vacuum! You can never create a vacuum (or anything even close to it) in a computer case. The negative (or positive) pressure is slightly different from the pressure outside. The density of the molecules will not be that much different.

Warm air rises in a case. It makes sense to use an exhaust fan to remove this warm air from the case. The removed air will be replaced by cold air coming in from anywhere. This is the basis of how a negative-pressure case operates.

In a positive-pressure case, air leaves the case from every hole! Some of the air that leaves is warm. But, some of it is cold. This is because you have no control over where the air leaves the case. You have control over where air comes in. This is the only advantage of a positive-pressure case, where you can place an air filter on the intake fan(s). Then, you can better control dust accumulation in the case.

Of course, you can have an exhaust fan in a positive-pressure case. So, that will force some warm air to be removed from the case from the top. But, it has been reported over and over again that if you have similar thermal performance, your positive-pressure system will be louder. If you have similar noise, your positive-pressure system will be warmer.

 

[m1ldslide1]

I modded my Cavalier3 case to have a 120mm and a 90mm intake; and then 120mm and 80mm exhaust, plus the PSU 120mm fan for more exhaust. I have the stock CPU HSF.

My 3700+ which is OC'd to 2.8ghz idles at around 25-27C and gets up to 41C under load. These are the best temps I've ever seen on air, and I keep thinking about how they'll be even a little better once I replace the stock HSF with the zalman9500 which will blow directly at my 120mm exhaust.

I'm not sure if having the two intake fans makes my case a positive-pressure environment given how much exhaust I have, but it seems like having a lot of both keeps a lot of air moving through the thing (and dust probably) and gives me some ridiculously low temps...

 

[StrangerGuy]

Originally posted by: Navid
It is funny when someone compares a negative pressure computer case with vacuum! You can never create a vacuum (or anything even close to it) in a computer case. The negative (or positive) pressure is slightly different from the pressure outside. The density of the molecules will not be that much different.

Warm air rises in a case. It makes sense to use an exhaust fan to remove this warm air from the case. The removed air will be replaced by cold air coming in from anywhere. This is the basis of how a negative-pressure case operates.

In a positive-pressure case, air leaves the case from every hole! Some of the air that leaves is warm. But, some of it is cold. This is because you have no control over where the air leaves the case. You have control over where air comes in. This is the only advantage of a positive-pressure case, where you can place an air filter on the intake fan(s). Then, you can better control dust accumulation in the case.

Of course, you can have an exhaust fan in a positive-pressure case. So, that will force some warm air to be removed from the case from the top. But, it has been reported over and over again that if you have similar thermal performance, your positive-pressure system will be louder. If you have similar noise, your positive-pressure system will be warmer.

From my experience, case cooling, either of positive or negative pressure, works well only when you have a large air intake . Otherwise the pressure inside the case drops very significantly and reduces amount of air available for cooling and components runs hotter than when the case is open. Not good.

A good benchmark is to touch the surfaces of the casing. If should feel cold to the touch if your ventilation is good.

 

[StrangerGuy]

Originally posted by: m1ldslide1
I modded my Cavalier3 case to have a 120mm and a 90mm intake; and then 120mm and 80mm exhaust, plus the PSU 120mm fan for more exhaust. I have the stock CPU HSF.

My 3700+ which is OC'd to 2.8ghz idles at around 25-27C and gets up to 41C under load. These are the best temps I've ever seen on air, and I keep thinking about how they'll be even a little better once I replace the stock HSF with the zalman9500 which will blow directly at my 120mm exhaust.

I'm not sure if having the two intake fans makes my case a positive-pressure environment given how much exhaust I have, but it seems like having a lot of both keeps a lot of air moving through the thing (and dust probably) and gives me some ridiculously low temps...

If your exhaust airflow when the case is closed feels the same, or even stronger than when the case is open, and the whole casing feels cold to the touch, your ventilation is excellent!

 

[HybridSquirrel]

well my fan orientation( i switched it around) 120mm intake. 90mm side pannel taking air from the cpu heatsink. 120mm exhaust for extra. and the 2 psu fans near the top to blast out the warm air rising


EDIT: see my fancy ms paint diagram

http://img136.imageshack.us/img136/3746/1014zo.jpg

 

[StrangerGuy]

Originally posted by: HybridSquirrel
well my fan orientation( i switched it around) 120mm intake. 90mm side pannel taking air from the cpu heatsink. 120mm exhaust for extra. and the 2 psu fans near the top to blast out the warm air rising

I bet you will get the lowest temps when every fan except the rear and PSU blows into the case. Mind trying it out?

 

[HybridSquirrel]

that leads to dust build up. i had the 90mm facing in. and the 120 and dust was a huge problem. ill try out this way for a little while it seems nice. my cpu is idling around 33c and my chipset is 45c(10c cooler) i posted up a diagram

 

[LOUISSSSS]

thats nice.. kepp your aspire psu then maybe u can get some crossfire in there too. oh and its just a few months old

 

[iRONic]

Originally posted by: LOUISSSSS
thats nice..

Well, duh. It's very stable, very fast, and very nice.

Originally posted by: LOUISSSSS
kepp your aspire psu then maybe u can get some crossfire in there too.

I don't need/want your permission to *kepp* the PSU. It's an nForce motherboard, genius. Crossfire won't happen on that platform.

Tell ya what, if you wanna keep raggin' on my system PM me. Stop kludgin' up the guy's thread on fan positioning.

 

[HybridSquirrel]

I LIKE UR SYSTEM