120 mm fan on bottom of case? i need help figuring out airflow paths

[Glow]

Im looking to do some air flow mods on my midsize case. Right now my computer is 7 degrees cooler just by taking off the side of the case, so it needs some work.
Things I have decided on:
1. 120mm blowhole on top of case
2. leave 80mm exhaust back of case (its a sunon and it feels strong enuf not to need to replace)
3. leave the power supply fan as an intake because it has a 2 year warranty i want to keep and i cant take off the case of it without breaking a warranty seal.
4. make an acrylic window over the cpu and pci area (and put a neon inside but thats irrelevant).

I want to figure out where to put my intake(s).
The front of my case is set up in a way I cant really put a big fan on, so the best I could do is 2 (or even 4, but i think that would be overkill) 60mm fans. I dont know if these would be good enuf for my only intake. Also, I havent seen aluminum filters for 60mm.... Would it be better to have the intakes near my cpu and video card? Then I would have to put them in the middle of my window though...I could put one 120mm or two 80mm's there. And if I do that, then will there be a lack of air flow in the front of my case for my harddrives? Another option is to put a bigger fan on the front lower side of the case, but here the fan would be blowing against the other side of the case and that might be kind of wasteful and the air wouldnt move as fast to the exhaust? Maybe I should put 2 60mm's on the front of the case AND have a 120 or 2 80s over my cpu area? Anyone have some advice? The only problem I have with putting fans over my cpu and video card is that they will block part of the window, but I want it to look bitchin' Damn sorry that was such a long read, i tried making it short but looks like i failed.

 

[Glow]

Oh yeah I forgot to mention the whole 120mm on bottom of case idea. I thought maybe I could use some kind of feet or wheels to raise the computer like 3 inches in the air....then I could put a fan on the bottom for an intake and have a good bottom to top airflow. Would that be enough space for the fan to suck up air well or not?

 

[dew042]

balance my friend! balance.

you have to take into account static pressure. basically you can only blow out the amount of air you can draw in. the fans blowing air in should be equal to the power of the ones blowing out. you can have 15 rear and top blow holes, but their performance is nothing if they don't have intake fans to supply them with aire to exhaust.

its more complicated than that, but that's the basic idea....

additionally the best cooling idea is the basic L shape. low intake in the front and high exhaust in the back. a rear intake and exhaust will not work. the air flow pattern will not work.

good luck.
dew.

 

[MonstaThrilla]

Here is what I'm proposing for my setup:

2 80mm front bottom intakes to cool the HD
1 92mm side intake to cool mobo (particularly system and vidcard RAM)
1 80mm Exhaust on the back
1 80mm Exhaust on the Enermax PSU, sitting right above CPU (I think its 80mm)
1 92mm Blowhole on top

 

[Lithium381]

yeah, that PSU as an intake really throws things off.....also, i woudln't suggest sticking a 120 on the bottom, it would draw in tons of dust, i geuss you could get a filter, but that would throw off airflow. and a 120 BLOWhole on the top? that means blowing in???? i'd use that to take out, and then shove those 60mm's you were talking about in the front. stpuid psu warranty....

 

[salman327]

Blowhole means exhausting air

 

[Lithium381]

wow, i've been confused about that, what's the alternate for intake? such that blowhole:exhaust :: ????:intake

 

[salman327]

Yeah I've been confused a couple of times before, until I asked someone and they told me what the hell blowhole meant. I don't think there is an alternative name to intake.

 

[Mikendi]

Every one want's to blow air out the top I was thinking if you're moving massive amounts of air why not bring it in at the top and out at the bottom? The "Heat Rises" theory is fine in a static environment, but get that air moving and I think that changes the equation somewhat. Any ideas???

 

[Lithium381]

good point, all that turbulence would definitaly affect airflow and the common "law" that heat rises.....i've never actually thought of it like that! well, if the airflow is done correctly, it goes from point A(probaby bottom front of case) to point B(back top of case) and carries the heat with it, then expells it from the system, that's what has been quoted as "nominal" the L shape as stated above...logicaly that works well. i think i'd stick with the method most people use, and just "accept" heat rising and use that as part of the design equasion. it'd be interesting to see how the intake on the top affects it, anyone willing to do a small test!? also, if someone has a window, is there anykind of non-harmful "smoke" product you could let into a blowhole and watch it and see where the air is actully going!? anyone done that?

 

[L8CS]

<<The &quot;Heat Rises&quot; theory is fine in a static environment>>

Even though the inside of the case is a non-static environment, the external air around the case is usually static. Therefore the colder air is at floor level and warms its way up.

If you reverse the flow of the blowhole in Glow's case, it may be beneficial because of his PS's setup. He should also reverse the flow on his 80mm exhaust on the rear so his blowhole (intake), Ps and exhaust are all pulling fresh air in at the top. He could use a 80mm at the top for his blowhole(intake)and still use the 120mm at the bottom for exhaust. By using the exhaust at the bottom, it would not draw dust into the case.

 

[Mikendi]

That's a nice idea like using your case for &quot;wind tunnel&quot; testing. A harmless vapor can be released for testing maybe dry ice as it's only C02. While on the subject of balance should one add up the combined CFM of intake and equal that with exhaust? I think it's probably better to err on the side of more exhaust you case naturally leaks and many are vented.

 

[Lithium381]

L8CS - good call, that would probably work very nicely, using the 120 on the bottom doing reverse of &quot;standard&quot; flow.....yeah, heh, wind tunnel! on the topic of balancing cfm....i think i'd much rather have excess intake, since it's easier to force that out with the exhaust fans, but the exhaust fans would have a harder time pulling air from outside the case if there were a slight vacuum within the case. dry ice, now there's a sweet chemical, hehe, i dont' have a window in my case!! i woudlnt' be able to watch..

 

[salman327]

Well I don't know your setup buddy (Primarily because I'm too lazy to read it), but whatever you do, try to keep your intake in the lower front, and exhaust at the top back, because you'll be drawing in colder air like that. And yes, you want more intake than exhaust if it can't be equalized. However your current setup might negate what I have just said, so ignore me then.

 

[Lithium381]

SAL - yeah, so far his system seems like a weird one, mainly b/c the psu fan blows down, throws off the standard flow in which yes the intake would be bottom front(mostly)...so instead of having the normal L shape flow, what has been suggested is just a straight down from the top/back and out the bottom/front, basicly the reverse L, although, on the 120 on top and the ones on back, cut away the metal completely, and use a filter of somekind that won't restrict airflow....such as a pair of nylons, to catch dust and cat hair and misquitos, small rodents that try and get into your computer, stuff like that, also find a non restrictive finger guard so you don't have an injury... fan guards are avaliable here, one of many places, this is just one i've dealt with personally, so i'm recommending it, as it worked great for me!

 

[L8CS]

Another factor is that were not dealing with an airtight case. The exhaust fans are dependent on the intakes but will compensate on inadequate inlet airflow by pulling from openings in the case. The exhausts will pull air from the path of least resistance, which in this case would mean from the removable side seams, the vent openings in the sides if applicable and around the card slots. Additionally, it will pull it from the drive bays if needed. So it's best to try to balance the airflow if possible.

 

[Lithium381]

Balanced is *best*.....but i was thinking, woulnd't it be best to have pressure....so that air would be circulating everywhere in the case, as the air has to go somewhere, so it goes everywhere tyring to get out(heh, personification)...with equal(which is very hard to obtain), air would flow in the same &quot;pattern&quot; would it not? as with to much exhaust, wouldn't there be small packets of unmoving air, since it would be rushed to get out, since there is more exhaust, it jsut gets pulled out pretty quickly? plz correct me if i'm wrong....

 

[Mikendi]

No - I think pressure will have the opposite efect and cause hot spots. Think of a venturi and when you draw air through it it creates a vacuum by means of negative air pressure. In theory you could have only exhaust fans on one end and strategic inlets around the case in effect creating a vacuue and drawing hot air out. One could induce fresh cool air to the CPU from the rear fan port via ductwork. Sounds complicated, but I'm going to play with this idea in the near future. Noise is as much a factor as heat, not to mention stress on the PSU.

This is fun - it's good to invent

 

[Glow]

if you want air straight to your cpu then just put an intake fan right over it on the side of the case....thats closer than the rear fan, i guess it depends which way your hsf fan blows, mine blows into the cpu.

 

[Lithium381]

yeah, i was thinking the same thing, ducting directly to my cpu, looked around for ideas, so far i've seen you can get flex tubing from automotive shops for pocket change then somehow mold it to a fan....let me know if you have any grand ideas as i'm open!

 

[mstudd]

I put an 80mm fan in the side cover over my CPU with a duct, directly onto the CPU fan, and it lowered my CPU temps 5degC.
I believe also that a bit of extra intake air is good to circulate cool air to the areas of the case that don't have good air flow.
As previosly stated, the air will take the path of least resistance (from the inlet fan, directly to the exhaust fan), so slow it down and it will fill the case better.
It works in automotive engines, so I like to think it applies to some extent here.

 

[Lithium381]

what'd you make your duct out of?

 

[L8CS]

<<One could induce fresh cool air to the CPU from the rear fan port via ductwork>>

Global Win makes a ducted HSF that's interesting, although it's for a Slot A. Its based on the VOS32 and has 60mm fan that pulls heated air from the HSF and blows it out the rear of the case, if I understand their diagram correctly. You could probably use the same concept and reverse the fan to pull fresh air into the HSF.



VOS32 Fan Duct

 

[Mikendi]

You could make one out of sheet metal, or copper, or plastic. I saw some nicely crafted ones a while ago, but can't find the link now

 

[mstudd]

Lithium381, I made my duct fron some PVC pipe fittings I got from the plumbing hardware store.
I found a fitting with a 75mm ID. with a collar that I modified to screw onto the fan through the normal mounting holes, and then another fitting to extend that to the HSF.
It cost about four Aussie dollars.
I assume you have the same sort of stuff where you live.