Questions about airflow+cooling

[l Thomas l]

Negative pressure is better right? (more outtake than intake)

How much cfm is enough? What rpm? I was thinking I'd just get a 800rpm one, since it's quiet. I would maybe move up to 1200rpm because I doubt I'd mind the noise much. I wouldn't be doing too much overclocking, maybe a little on the CPU (3800+ X2).

Also I was reading a really old sticky on OCForums and it says something about cutting off the fan grate in the front, which isn't visible from the outside of the case. Do they still have these now? I thought there's just air filters.

Thanks

 

[VinDSL]

Originally posted by: l Thomas l
Also I was reading a really old sticky on OCForums and it says something about cutting off the fan grate in the front, which isn't visible from the outside of the case...

"Grates', e.g. blowholes that are made out of drilled holes, louvres, and such, will kill your air flow big time! It's the hallmark of a cheap case, and ppl that buy these things usually don't even install case fans, so...

Yes, cut 'em -- front and back!

 

[l Thomas l]

What if it has one of those stupid front doors? That must kill airflow too. But then the P180 has a front door and no one complains.

Looks like this has front grates too. Maybe it's an air filter? http://www.newegg.com/Product/ShowImage...ATX+Mid+Tower+Computer+Case+%2D+Retail

What about this: http://www.newegg.com/Product/ShowImage...ATX+Mid+Tower+Computer+Case+%2D+Retail

That's a grate on the back.

I'm not sure what you mean.

Oh... do you mean things like this: http://www.newegg.com/Product/Product.asp?Item=N82E16800999364
?

Added on?

 

[l Thomas l]

Also when you buy a case, when it tells you how many fans there are, that means it doesn't have a reserved space to add more in terms of case fans, correct?

 

[AyashiKaibutsu]

Originally posted by: l Thomas l
Also when you buy a case, when it tells you how many fans there are, that means it doesn't have a reserved space to add more in terms of case fans, correct?

On newegg usually the number of fans indicate how many it comes with and not how many slots are available.

I've always though positive pressure was better. If you have negative pressure you get stuff like dust collecting around your DVD drives since every hole that isn't a exhaust becomes an intake to some degree.

 

[l Thomas l]

Damn! How do I check the fan slots? This whole time I've been looking for a case with *2 120mm fans* selected on Newegg. I ended up finding this: http://www.newegg.com/product/product.asp?item=N82E16811147039

But there must be a cheaper case with 2 120mm fan slots 1 in front 1 in back. I bet there'd be a cheap CoolerMaster. Damn.

BTW I decided to go with a front and rear 120mm fan so I can always adjust the fan speed later anyway to adjust the pressure.

 

[Operandi]

Negative air pressure is bad.

You want neutral or slightly positive, to control the air flow and prevent dust bunnies, deer, and mongooses.

 

[Howard]

Doors don't necessarily impede airflow. There are intake vents around the front door of the P180... and a lot of cases have half-doors where air goes in the bottom half.

 

[l Thomas l]

Originally posted by: Operandi
Negative air pressure is bad.

You want neutral or slightly positive, to control the air flow and prevent dust bunnies, deer, and mongooses.

I know it's old but..
http://www.procooling.com/index.php?func=articles&disp=71&pg=1

Meh. I'm gonna get 2 120mm fans anyway so it can be balanced, and then play with the pressure a bit if I need to.

 

[VinDSL]

Okay, I read that article twice...

This self-described 'hardass' has an axe to grind and needs to get above his emotions if he wants to be taken seriously. That's the way I look at it! Still, he made a couple of valid points...

• In reality, virtually all of the cooling of PC cases occurs due to air movement.

• Dell servers and workstations often have elaborate ducting to pull heat from the CPU out the exhaust, but still operate sans intake fans.

In essence, air movement DOES DO all the cooling, and exhaust fans are more important than intakes. Those points are indesputable -- everything else he said was.

I would submit to you, once again, that trying to push air through drill holes, et cetera, does NOTHING to enhance its' movement!

 

[0roo0roo]

What if it has one of those stupid front doors? That must kill airflow too. But then the P180 has a front door and no one complains.

depends on how its designed. the antec silent cases have baffled vents in the front, to the sides of the doors or below. theres plenty of airflow, its about total vent area, it doesn't matter if its clustered or not. the p180 is known to cool very well. custompc magazine used thermal cameras to test cases, p180 was one of the top cases.

 

[natethegreat]

COOLER MASTER Centurion 532This case is setup with 120 in front and an optional 120 in back

Antec SLK3000-B Has a 120mm exhaust and optional 120mm intake. Check out the Antec Solo or NSK 6500 if you don't like front panel doors.

RAIDMAX X1 Comes with rear 120mm exhaust and side window 80mm intake instaled, and has an optional 120mm intake. AnandTech X1 review

These cases all have good airflow and are not that expensive.

Try googleing case cooling guides for more info on cooling techniques.

 

[0roo0roo]

fans 101 onthe side is still good
http://www.dansdata.com/hx45fan.htm

 

[Suspicious-Teach8788]

Negative pressure = more dust. That is obvious. Honestly, negative or positive is up to you. You need to check the temperatures adn what effects there are. I know a lot of people tell me negative is good, and there are a good number of poeple who will tell you positive pwns. Go check both out...

 

[l Thomas l]

Thanks guys. I'm still not sure what you mean by the fan grates though. I thought all cases have the grate that covers the fan?

 

[m1ldslide1]

Originally posted by: Operandi
Negative air pressure is bad.

You want neutral or slightly positive, to control the air flow and prevent dust bunnies, deer, and mongooses.

Is there really a problem with dust if you have canned air close by that you use regularly?

Seems like negative air pressure keeps warmer, stale air from hanging around in your case longer than it has to. Obviously you wouldn't want it so negative that your system is starved for airflow, but just negative enough so that all of your air is moving.

Thanks guys. I'm still not sure what you mean by the fan grates though. I thought all cases have the grate that covers the fan?

Yeah, all of the cases I've seen don't leave rapidly spinning fan blades exposed to the open air. Sounds like the grates that are problematic are the ones that aren't open enough, and so impede airflow. Those are the ones that you could consider cutting or further perforating. I'd avoid removing them completely unless you have no pets or little people running around...

 

[m1ldslide1]

Originally posted by: l Thomas l
Negative pressure is better right? (more outtake than intake)

How much cfm is enough? What rpm? I was thinking I'd just get a 800rpm one, since it's quiet. I would maybe move up to 1200rpm because I doubt I'd mind the noise much. I wouldn't be doing too much overclocking, maybe a little on the CPU (3800+ X2).

I can't answer how much cfm is 'enough' and so forth, but I can tell you my experience. I have a 90mm lower intake at 40cfm, a 120mm upper front intake at about 45cfm, and then a 120mm rear exhaust at 110cfm (when its cranked, which is all the time this summer) and a PCI slot exhaust rated at about 40cfm. (Also my PSU has a 120mm exhaust, not sure what cfm). I have a lot of fans, and my system is really loud, but I stopped seeing big drops in temps a while ago. In other words, I went to great lengths to try to get my system as cool as possible on air, but 3 fans and 8 zipties ago was only about 3 degrees warmer:
90mm intake, 120mm exhaust (50 cfm), 120mm PSU exhaust.

So IMO you don't need to go too overboard, especially if you're not trying to squeeze every last Mhz out of your chip. But if you get started on a system and have an idea what you want your temps to eventually be, you can always tweak it as you go.

 

[l Thomas l]

Originally posted by: m1ldslide1
Yeah, all of the cases I've seen don't leave rapidly spinning fan blades exposed to the open air. Sounds like the grates that are problematic are the ones that aren't open enough, and so impede airflow. Those are the ones that you could consider cutting or further perforating. I'd avoid removing them completely unless you have no pets or little people running around...

How am I supposed to know if it's not open enough?

 

[m1ldslide1]

I'm not sure what to tell you on that one - I haven't heard of a home CFM measuring device where you could see if you're really getting the throughput that you're looking for. I guess you could power on the fan with the grill and see how it feels on your hand and check your temps. Then remove the grill and repeat. If there's enough of a difference, then figure out a custom solution for yourself.

 

[CreepieDeCrapper]

Originally posted by: DLeRium
Negative pressure = more dust. That is obvious.

this isn't very obvious to me for some reason... if i'm understanding correctly, then negative pressure means more exhaust than intake which, in my mind, means more dust LEAVING the system than entering it

seems to me that a greater positive (i.e. intake) pressure would yield greater dust build up as there won't be enough airflow to exhaust all the dust away from the system that the intake fans are drawing in

what do i have wrong?

 

[natethegreat]

Positive pressure systems if implemented correctly only let air in through the intake(s), wich are filtered to prevent dust from entering. Negative pressure systems create vaccums wich make it impossible to filter effectively because air will enter the case from any crack/gap it can find.

 

[CreepieDeCrapper]

Originally posted by: natethegreat
Positive pressure systems if implemented correctly only let air in through the intake(s), wich are filtered to prevent dust from entering. Negative pressure systems create vaccums wich make it impossible to filter effectively because air will enter the case from any crack/gap it can find.

i get it now... i wonder, though, if you negate the dust factor (i.e. in a "clean room" with no dust particles or, more practically speaking, by cleaning the inside of the pc weekly) if negative pressure is more effective in removing heat and, in general, cooling the system down?

iow, dust can interfere with proper cooling, but if you remove the dust problem, what is the best way to cool?

 

[l Thomas l]

You can put dust filters in front or behind the fans, and then clean them.