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 Post subject: Exhaust fans badly positioned
PostPosted: Thu Jan 02, 2003 9:16 pm 
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My ATX midi tower case and many cases I have come across have the exahust fan poorly positioned. From my non scientific experiment by placing my hands inside the case at different positions while the PC is running, I notice the hottest area is just above the heatsink and below the PSU.

It seems like a lot of hot air is trapped between these point. When I feel the air coming out of my exhaust fan this confirms it, where the uppermost of the fan is blowing warm air, specially the corner adjacent to my HS and the rest of the fan is blowing relatively cool air. This makes a lot of sense since hot air rises and if you power supply is not sucking up the air it would be trapped there. 2 fans PSU would help this situation but this will cause unwanted extra noise.

Ideally the best postion for the exhaust fan would be directly below the PSU and towards the motherboard. As this is not possible since the keyboard/mouse and other sockets are in the way

Why don't they case manafactuers realise this and place it just below the PSU?

It really makes no sense where it is positioned, is it not better to suck out more hot air than cold air?

Anyway I am going to try to find a flexible 'S' shape duct and attach it to my exhaust fan so I can get better cooling.


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PostPosted: Thu Jan 02, 2003 9:32 pm 
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my HP case has a duct that sits right over the HSF. The fan was crap, and eventually got tossed. From what I could tell, it was an intake, not an exaust. The PSU was mounted on a detachable metal plate that went above the PCI slots.


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PostPosted: Fri Jan 03, 2003 1:00 am 
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dells have ducts from the heatsink to the back exaust. My moms dell computer has one slow moving nmb 92mm fan for exaust positioned over 2.4ghz processor and the air coming out always seems cool so i guess its doing its job, its not silent but its damn quiet, i can only hear it at night cause during the day background noise drowns out the little bit of air turbulence the fan makes.


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PostPosted: Fri Jan 03, 2003 11:00 am 
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What's the take on cases with an exhaust fan at the top of the case? Does that placement allow the hot air that's "stuck" around the P/S to more readily escape? Would it be useful to have such an exhaust port even w/o a fan? Anyone with practical experience? :)


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PostPosted: Fri Jan 03, 2003 11:11 am 
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I'd think that having an exhaust port up top is just asking for more noise. Especially if you've got a fan there. Even if its just open, its a direct exit for sound.

I had to cringe when I saw a project at an overclocking site, they put a 170mm fan as a top mount exhaust port. Durn thing was rated at 120cfm or so. Geesh...


Zyzzyx


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 Post subject:
PostPosted: Fri Jan 03, 2003 12:52 pm 
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ez2remember wrote:
Ideally the best postion for the exhaust fan would be directly below the PSU and towards the motherboard. As this is not possible since the keyboard/mouse and other sockets are in the way

Why don't they case manafactuers realise this and place it just below the PSU?


I note that in the newest mid-tower case I've gotten, there is a rear exhaust port placed right below the P/S. My older mid-towers do not have any such fan port, since the P/S is in a different orientation. I've put a panaflo at that exhaust port and it does work to cool down the case and CPU a bit (as measured by onboard thermistors and lm_sensors).


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 Post subject:
PostPosted: Mon Jan 06, 2003 9:06 am 
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---

What's the take on cases with an exhaust fan at the top of the case? Does that placement allow the hot air that's "stuck" around the P/S to more readily escape? Would it be useful to have such an exhaust port even w/o a fan? Anyone with practical experience?

---

I have a top exhaust with the fan disabled. I can definitely feel warm air escaping from the exhaust after a long computing session.

As far as noise, covering up the exhaust with a book/hand/cdcase, etc has no noticeable effect for me, my biggest noise polluter (cpu hs) can still be heard at the same level/frequency. As soon as I replace my rather generic hs with a thermalright+7volt panaflo, I think I'll be reaching my personal noise tolerance acceptance level.

All in all it's nice to feel the hot air escape, and I do realize that because of that I'm able to run my components quieter but I'm not sure if the tradeoff between noise/heat helps or hinders the quest for powerful quiet computing since I don't have any reference systems to compare to.

Actually on further thought, I suppose the more passive heatsink solutions you have in your case (i.e. videocard with zalman heatpipe) the more important it is to improve overall case airflow.l


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 Post subject: Zalman takes care of this
PostPosted: Fri Jan 10, 2003 6:31 am 
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If you have a normal case, the Zalman 300A will solve your problem. It's got a flow-through design on both the bottom and the back, thus allowing the hot air to exit your case through the power supply.

From experience, I can make this recommendation: Use one intake fan at a high flow rate (preferrably a side fan) and one exhaust fan at a lower flow rate (in most cases, this should be the power supply's fan). Slightly positive case pressure is good! (if you don't believe me, try using an exhaust fan on the side of your case, and watch your CPU scream for help)

Most people who are trying to silence their computers are actually concentrating too much on cooling and end up using too many fans. I'm not saying this is always the case, but I've already caught myself doing it.

With the Zalman design, the PSU fan will speed up as necessary so the components don't die. Also, the trapped air will make its way out through the power supply. An extra exhaust fan can actually make matters worse becase it is stealing air from the case (particularly from the CPU), and cooling capabilities could be reduced dramatically. So remember, think positive (case pressure, that is). And more fans != better.

-Bryan


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 Post subject:
PostPosted: Sat Jan 11, 2003 11:51 am 
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If you take the ATX spec into account, the best place for an exhaust fan to remedy the said problem is on the PSU.

ie "inline" with the normal PSU fan but on the inside of the case.

I find cutting a hole in my PSU and mounting a fan as described is quite good for exhaust, the air from the CPU is sucked straight out instead of drifing through a few tiny holes in the back of the PSU.


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 Post subject:
PostPosted: Sat Jan 11, 2003 3:31 pm 
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Location: United States, Mobile, AL
Yea i wonder why they dont make power supplys like that? If they just completely got rid of the outside exposed fan and put one on the back of the power supply instead then not only would the noise be eminating from deeper in the case (less noise) the fan blowing onto and through the power supply would cool it better too.


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