Best Option for Airflow in a PC

[Skoodog]

I'm trying to find the most efficient way to cool my PC with as little noise as possible. I've argued with my friend over whether to make certain fans intakes or exhausts. I'm gonna try and explain this in ASCII the best I can:


__________________
<---| <--- | |
|___\| ______ | C
| _\__ | _---> |--->
A || | | ^ |
??? --->|| |___| ---l |
| ^ |
| | |
| L----- || B
|_________________||<----

This is a VERY rough sketch of how I perceive my rig is cooling itself. (Sorry, I don't want to invest an hour in ASCIIing it better.) I have a PAL 8045 HS, two High volume Panaflos at A and B, and a bay cooler at C (it pulls air from the two empty bays underneath it). I have an Athlon XP 1700+ Tbred on an nforce NF7-S 2.0 board. So overall I have two questions:

1) is my current cooling theory set up in the most effective way?

2) should fan A be an exhaust or an intake? (it's actually not installed yet...I was waiting for my new PSU...just put an Antec SL350 in which is far superior to the no-namer with no bottom fan on it.)

Thanks!

 

[Skoodog]

DAMN! Tabs screwed my diagram.

Let's try again:

______________
<--| ^ | _____| C
|__|__| |_____| --->
??? || SSS ^ |
A || SSS | |
| |
| <--- ||
|_____________ || B

Rougher this time but you get the jist.

Also could the bay cooler be more efficient with a ducting mod forcing more air to come from the CPU area?

 

[Skoodog]

dammit, I give up. Hopefully I get the idea across.

 

[Peter D]

try makin a quick pic in paint or something..?

 

[0roo0roo]

if you had spent that time just describing your setup, you would have saved time. i don't know what the hell that asci is supposed to look like, its gibberish.

you try to balance airflow. its best to have slightly more intake then exhaust. fans suck at fighting back pressure.

the bay cooler better be bringing air in from the outside, or its useless. bay coolers are generally loud and not worth the noise they make for the cfm. then again you have high volume panaflows which aren't exactly silent.

ok, enough ranting.

yes, the ps fan counts in terms of air pressure.


http://www.dansdata.com/hx45fan.htm dan is the man read the strip on the side, its still relavant for cooling.

A fan will deliver its maximum airflow when it's hanging in space - the so-called "free air" situation. It will deliver its minimum airflow - zero - when it's blowing into a sealed box. In the sealed box situation, all the fan can do is move a bit of air into the box, increasing the air pressure inside, and keep it there. These two kinds of fan behaviour are governed by the two fan performance statistics - pressure and airflow

All computer fans are roughly the same shape, so their pressure and airflow statistics are roughly proportional to their size and thickness. Different kinds of air moving apparatus have different pressure to flow ratios - a "blower", for instance, which uses an enclosed impeller to push air out of a port, has a higher pressure rating but lower airflow than a fan of equal power. A hair dryer is a good example of a blower. It's also possible to buy small 12 volt blowers which can be used in computer applications, mounted inside the case to direct a well-aimed stream of air at something that needs cooling, like a CPU.

A computer case is neither a free air nor a sealed box situation. A really well ventilated case looks to the fan pretty much like the free air situation; the more tightly buttoned up and packed with cables the case is, the more like a sealed box it behaves. The lousy mounting locations of many case fans don't really make a lot of difference to the behaviour of the box, but they reduce the effectiveness of the fan; a poorly mounted fan behaves like a less powerful one.

Arranging fans physically in parallel - next to each other, blowing in the same direction - gives twice the airflow, but only in the free air situation. The closer the thing they're blowing into is to a sealed box - the higher the "system resistance" - the smaller the parallel fan improvement becomes. Any number of identical parallel fans blowing into a sealed box will do no more than a single fan.

Arranging fans in series - stacked on top of each other, so one blows straight into the other - gives the opposite situation. There's no improvement in free-air performance, but double the pressure increase in a sealed box, and better and better performance compared to parallel fans as the system resistance gets higher and higher. Incidentally, this means that those goofy monster processor heatsinks with layered low-profile fans are a waste of money, since fans strapped onto a heatsink are very nearly in the free-air situation, and putting two layers of them there does close to nothing to the airflow.

So series fans can pump more air into a box with poor through-flow, but parallel fans will do better in a box with high through-flow. When you arrange one fan blowing into a computer and another sucking out, you're basically making a poorly sealed serial fan arrangement. The PC box leaks all over the place, so not all of the air the blowing fan puts into it exits through the sucking fan, but the arrangement is much more like serial fans than like parallel ones. This is good; it keeps the airflow up even in the card-and-cable-packed mess that is many PCs.

The exact fan arrangement to use therefore varies with the box, if you?re going for maximum efficiency. The easy way around the problem is simply to go for overkill, mount much more powerful fans than you need, and have done with it. That's certainly what I settled on. As long as the fans aren't blowing components out of the back of the computer, the problem is solved. The problems with this solution are that big fans are more expensive, computer power supplies can be overtaxed by multiple fans (a problem you can solve by using a mains powered fan), and big fans make more noise than many users will tolerate.

12 volt fans with a three-pin connector plug into the special three-pin headers on recent motherboards and can thus report their rotation speed - if the speed drops, an alarm can sound. Some fans have the three pin plug but only two wires; they'll run from a motherboard fan connection, but won't report their speed.

In the near future, we should be seeing PCs with efficient ducted cooling built in. Ducts allow the cooling air to go where it's needed, and some fanatical overclockers already use duct arrangements of varying degrees of gimcrackness to keep their sweating and terrified components cool.



in one of his other articles he tests his cooling setup using a smoke blower i wish i had one of those to see airflow.


and zip ties are your friend. a mess just impeeds air flow

 

[sodcha0s]

its best to have slightly more intake then exhaust. fans suck at fighting back pressure.

Not true. If you have more fans blowing in than blowing out then you are creating positive pressure inside of the case, which reduces airflow. Yes, it helps keep dust out, but will raise temps. How much the temps raise depends on a lot of things. It's just like that 'sealed box' situation in the quote you posted...

A fan will deliver its maximum airflow when it's hanging in space - the so-called "free air" situation. It will deliver its minimum airflow - zero - when it's blowing into a sealed box. In the sealed box situation, all the fan can do is move a bit of air into the box, increasing the air pressure inside, and keep it there. These two kinds of fan behaviour are governed by the two fan performance statistics - pressure and airflow

If you have more fans blowing out of the case, (exhausting) you then get a slightly negative pressure inside and therefore the intake fans will be able to supply the case with more cool air from outside. Temps will be lower in this scenario.

 

[pspada]

But what about the big floor fan I have blowing into the front of my case?

 

[0roo0roo]

Not true. If you have more fans blowing in than blowing out then you are creating positive pressure inside of the case, which reduces airflow. Yes, it helps keep dust out, but will raise temps. How much the temps raise depends on a lot of things. It's just like that 'sealed box' situation in the quote you posted...

yes, perhaps i should have expained that, i thought it was in the quoted text though. negative pressure isn't good for fitlters or dust. and of course i was talking about a very slight positive pressure, otherwise it would have gone against everything i had quoted about backpressure.

 

[beatle]

I've not seen a fan setup work more efficiently than a hole in the side of the case with a case fan in it blowing directly onto the CPU. If you're even moderately handy you should be able to pull this off.

 

[Skoodog]

I unfortunately am not even moderately handy. I was looking at perhaps buying a sidepanel with the fan in the side but I don't want the computer looking more ghetto-dog than it already is (you all can keep your boxes that look like their signaling extra-terrestrial life - I'll keep my "computer-looking" computer ). My location for my rig is also under a desk, which does not get very good airflow but also manages to keep cool somehow (I don't know how that works but it worked all through college and is still working for me today).

If anyone knows where I can get sidepanels with pre-fanned holes I would be most grateful with a link.

Re: the bay cooler, it is an exhaust with the fans pointing down. It really probably is the most efficient fan in my rig pumping out around 75 cfm, however I do realize it is in a rather bad spot. This is where I was wondering if perhaps getting one of those thermaltake ducting mods, screwing/hotgluing it onto the fan-hole, and sucking air more directly from the CPU/HS area. While I'm not moderately handy, I've found anyone can operate a glue-gun. If I do end up doing this, would it be enough to fasten the ducting mod to the housing of the bay cooler, or should I dismantle the cooler and take the fan out and put it on the duct like they say in the instructions for heatsinks?

I apologize again about the rotten ASCII. All your comments are quite helpful.

 

[0roo0roo]

there are many fan hole tutorials online. many many. cleanest way is to buy a drill and buy a hole saw bit. it'll cut a hole of 80mm or whatever bit you choose in one go. then you just have to drill the screw holes which is rather easy. its pretty straight forward, esp with tutorials. then you either finish it off with the cstrip moulding or car door protector edging.

 

[beatle]

I didn't even bother finishing the holes I cut in my server or the hole I cut in my brother's tower. I used a wire fan grille as a template (sharpie works great for marking on the case where to cut and drill) and then used a dremel to cut the hole. If you have a holesaw you'd probably get a better looking hole, but after the grill is installed you can't tell how rough it is and it's impossible to cut yourself. The results are well worth the effort.

 

[Skoodog]

I have an aluminum case...will a holesaw still work? I'd think that'd be a little crazy.

 

[Icewind]

Holesaw will work, but I use a dremel and jigsaw. I mask the ENTIRE area so nothing gets scratched cause as you move that jigsaw across the metal. I then take the dremel and make a start cut then proceed with the dremel. After that I use a dremel and grind down the edges.

 

[Skoodog]

Originally posted by: Skoodog

Re: the bay cooler, it is an exhaust with the fans pointing down. It really probably is the most efficient fan in my rig pumping out around 75 cfm, however I do realize it is in a rather bad spot. This is where I was wondering if perhaps getting one of those thermaltake ducting mods, screwing/hotgluing it onto the fan-hole, and sucking air more directly from the CPU/HS area. While I'm not moderately handy, I've found anyone can operate a glue-gun. If I do end up doing this, would it be enough to fasten the ducting mod to the housing of the bay cooler, or should I dismantle the cooler and take the fan out and put it on the duct like they say in the instructions for heatsinks?

What about this part of my comments...anyone recommend this or think the idea is solid?

 

[0roo0roo]

Originally posted by: Icewind
Holesaw will work, but I use a dremel and jigsaw. I mask the ENTIRE area so nothing gets scratched cause as you move that jigsaw across the metal. I then take the dremel and make a start cut then proceed with the dremel. After that I use a dremel and grind down the edges.

aluminum is softer then steel, its easier to cut.

yea i use a dremil too. you can print out fan templates from pdfs off the web. search web for fan template 80mm or whatever

dremil is possibly somewhat harder i guess since your doing it by hand, whereas a hole saw just makes a perfect hole for you. the templates i use are more like squares, with slightly rounded corners, which makes it easier for dremil cutting.


line the fan up with the hole you've made, and then mark the fan screw holes then you drill and your done.


and yes, i havn't bothered finishing the holes with c strip moulding liner for a while, i simply don't care but some people do.


your bay cooler really does 75cfm? sounds rather fishy to me unless its really loud. esp facing down the thing probably loses quite a bit of efficiency.


here's someof my ugly handiwork http://fox302.com/index.pl?s=vg&user=oroooroo&category=Case


i have another older case i actually bothered with moulding and stuff, but the case is no longer used anyhow. and as you can see, even if the fan won't quite fit inside because the cdrom wires are in the way, i put the blow hole on the outside its not entirely blocked under it or anything, just slightly not enough space for the corners of the fan