Air flow - How much is enough?

[Malpine Walis]

I am working on my first home build. Assuming that I was willing to have a jet engine in my living room, I could put 3 Delta 80mm EHE fans in the case and a YS Tech 120 mm fan in the top for a blow hole. Now I really do not want to do this but if I did, would all that air flow give me noticeably better cooling than a less aggressive (and quieter) system?

I tend to think that at some point, aggressive air-cooling must reach a point of diminishing return. The closer to room temp my case temp gets, the less payoff there would be in having more airflow.

Since I am asking a question that has a boatload of variables, what would help is to assume that I have already done what I can to get the best airflow (round cables, proper card placement, etc.). Then, if I could hear from people with similar systems telling me what fans they are using and what case temps result.

Necessary data: I am going to use a full tower case with 2 80mm fans at the front/bottom and 1 80mm fan at the back under the power supply (servercase.com, CK01F) and an atholon XP processor at a factory rating of 1600-1900.

[dreadlord79]

If you just wanting to keep the CPU itself cool; I would just put a duct in the side of your case so that it was dirrected right to your HSF. This way the fan on your HS will pull the air from the outside of the system right into the CPU keeping it cooler since it won't be breathing the already heated air inside of the case. If you are going for complete cool, go with your setup the way it you think with one difference, put the 80 from the below the P/S into the top plate of the case. Your P/S is already pulling out some of the hot air from inside of the case, so why not pull some more from nearer the CD and HDD? In any case, a duct can take temps down without to much more noise being produced. Hope this helps. :)

edit: PS~ you might also want to put some kind of screen in the duct for better air turbulance; which as I'm sure you know; will help take even more heat from your CPU.

[Malpine Walis]

Thanks for the tips dreadlord. Perhaps I could have said more at the top of the thread but I did not want to ask too many questions at one time.

As this is my first time building a comp, I want to keep it as close to a “normal” configuration as possible while still using all beefy parts. The closer I stay to that ideal the better my baseline data will be when I begin to over-clock.

While ducting would serve the purpose of keeping the CPU cool, what I am after is at what point more airflow would cease being useful. While keeping the processor cool is a worthy goal by itself, the processor is not the only heat source I am going to deal with and keeping the case temp low will keep everything cool across the board.

While ducting is generally a good idea, I think that that I want to reserve that for the next phase of this experiment.

>>>>

However, you do give me the opening to bring in one other idea I have been playing with. One of the fans that might end up in my baseline config could be an expansion slot cooler. Normally, these fans blow out but being DC, they ought to be easily reversed. If I did reverse one and put it over my graphics card, this gives me something like 40 CFM of room air right in one of the places that most needs it.

[dreadlord79]

Just here to help if I can. :) If you need anything else be a link or just want to bounce ideas around; just throw up another responce applied to me because I get e-mailed on all of the threads I post in.

[Yodums]

There should be at least 300cfm air flow in your case I usually recommend double or 1.5x the amount required ...

Espically for AMD I'd go for 600cfm.. Eh 5 120mm, 131.5 cfm YSTech fans 15 bux each!

[Diggrr]

MalpineWalis, hello and welcome.

You can't simply reverse the DC. You need to open the cooler and flip the fan(s) over. Don't forget the curvature of the blades. They work badly if just reversing the voltage. If it's a cage type blower, it won't work at all in reverse, it too has to turned around.
Besides, alot of DC fans won't run reversed polarity as they are brushless.

[Malpine Walis]

Yah,I know that big air flow gives big cooling. And the YS Tech fans do move a lot of air. They are also the loudest fans around. They are just as loud as the Sunon 120x25 HS but they move more about 33% more air.

What I am after is at what point more air flow just will not help.

Try this for an example:

What case temp are you getting with that set-up?

And what case temp might you get if you only had four huge fans?

>>>>

Edit: Fans may be cheap but are they worth the money I would have to pay?

[RoadWarrior]

Well you definitely want to stay subsonic! :D

Anything with an air velocity of below 150m/s shouldn't cause you troubles. That's around as fast as the fastest propeller planes can go.

if we roughly guess 30cuft to a cubic meter, then for a 120mm fan, area = .0.06^2 x 3.14159= 0.011 m^2 so 150m/s through that would give.... about 1.7 cubic meters per second or around 50cuft per second, so you're looking at 3000 cubic feet a minute being the most you want out of a 120mm fan....... as if.

Of course, you might need a heatsink designed for laminar flow or something :D

Hmmm, just wondering at what airspeed the boundary layer gets real hard to break up, that might be a prob, your high speed air might make a static blanket under it.........

Is there an aerodynamics major in the house?

Road Warrior

[Malpine Walis]

The case that I am going to be building in has an internal volume of just about 1.75 cubic feet. So 30 CFM would replace the air in the case a bit over 17 times per minute. Assuming perfect airflow, which I know is not going to happen of course. And 50 CFM would replace the air about 28 times per minute.

With fans alone, case temp can never be less than room temp. After I reach that point, no increase in airflow would provide further benefit. In addition, the lower the case temp, the less benefit I would get from further increase in airflow. Think of it this way: 20 CFM would be substantially better than 10 CFM. But 100 CFM would only be marginally better than 90 CFM.

What I am hoping to hear is what case temp would result from a given airflow.

[Maximus Nickus]

It all depends on the temps, if your say 1-3C off roomtemp then you have to think is it worth the extra $ on fans?

However if your a nutter like me your case will already be never above roomtemp!

[Diggrr]

It all depends on your style...Do you want a fairly cool, quiet computer, or do you want friends to say "where did you get that hovercraft"

Additional air cooling does provide diminishing returns. You can put in the first 200 cfm to shed 10 degrees off your system, but you may have to add another 200 cfm to get 1 degree lower still.
If you simply must have that 1 degree, add all the noisy fans you wish. If you just want more airflow but not at the expense of quiet or income, then look at the way the airflow is now.
Did you remove the stamped metal grilles on the fans you have now? Are there plastic cages on your fans? Is there room/desire to up the fan size? There are tweeks you can make to your existing setup without adding another component.

I don't think that anyone can say what temp you'll have at what cfm, there's just too many different combinations of equipment to wedge into the box.

[dreadlord79]

Heres one way to check your airflow (just a though so please don't yell;) ). If you really want to see what you need to do to get the airflow perfect. Get yourself a sheet of acrylic/plexiglass from your local hardware store, cut it to be the twin of your existing case side panel so you can see into the case. Now take and light some incense and place in front of the intake of your system. Turn on the system and watch were the "smoke" from the incense pools and how it flows. That would tell you right quick how to set it up just right. Like I said, just a thought. :)

[Diggrr]

Not bad, use a couple of pieces at once for more smoke.

Mmmmm, Sandalwood....Groovy!

[dreadlord79]

Yah, and if your room smells funny, it will help that to. Remember your computer Karma! :D

[Maximus Nickus]

A great way to rid the iffy smells......not saying that were all druggys though!!!

:rolleyes:

[dreadlord79]

Not me any more! That's my friend Mike who's a DJ had That little problem. :) I personally don't care what me you do in your own house as long as you don't hurt no one else.

[WyrmMaster]

My case has under 100 cfm of airflow, and it stays plenty cool, personally i would say that 150 is the max that you would need.

[BigBlockk]

I have a 1000MHz PIII running at 1125MHz in a no name baby AT case (I don't like big casses). It has two 5.25" drive bays that have a DVD ROM and a PlexWriter. It has a HD and floppy. It has a VooDoo3 3000 with a heatsink that runs VERY hot (even with a fan on it).

I tell you all of this to show that there are lots of places to generate heat in this little (7"W, 13"H and 16.5"D) box. The only fan in the case when I built this machine was the power supply fan (blowing out) so you see I had to plan well if I were to keep this little beast cool. Now I know that your CPU will run hotter than mine but your case is a lot bigger to.

I removed the case and carefully installed a (one that is) Sunon 120mm case fan with filter blowing directly at the AGP slot (the CPU is right above it). I then cleaned the stock Intel heatsink and remounted it with some Arctic Silver compound. I then reinstalled the case and it has been running Folding@Home ever sence (with the exception of shutting it down to remove some ram for another machine). This software runs the CPU at 100% 24/7. This provides for a good positive pressure inside the case to keep birt out because the only exhaust is the power supply fan and every crack and seam in the box.

I have had only 2 stopages (both heat related). This was when I cleaned the heatsink and used the Arctic Silver in place of the pad that came on it. Since then (about 3 weeks) it's been Folding right along.

If you get the idea that I don't think much of cases the size of barns with 57 fans in them, you'd be right. I think extreme case cooling is a little overblown.

If I were you I'd put a 120mm in the side blowing at the AGP slot and "maybe" one (1) 80mm blowing out the top just in front of the leading edge of the power supply. Remember, heat rises. Your box is actualy a chimney so, cool air in low, hot air out the top.

BigBlockk

Later.....

[adamtekh]

i keep my lil system , with its voodoo 3 3000 pci OCed, nice and chilly with 1 60 mm, 6 80 mm , 1 92mm its kinda loud when u got the delta @ 12 but it keeps it cool

never above 40c on the cpu with the windows open

and its a mid tower

:beer:

[Yodums]

I've heard for good airflow you should get at least 300cfm for the best cool air possible..

[Maximus Nickus]

Oh well I have 550CFM.....but hey its a BIG case!!! It never goes above ambient so theres nothing more I can do, heck even my Dimms have a Delta on them!