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Negative Case Pressure / Positive Case Pressure

G

GeeFizzleDizzle

Banned
When deciding which of these methods I'm going to use, do I need to count the PSU exhaust fan. For example, if I want to go with a negative case pressure setup and use one lower front intake fan, do I use one upper exhaust fan in addition to the PSU exhaust fan to make two or do I leave the PSU fan out of the equation and use two upper exhaust fans?

I hope this makes sense and someone can help me out. Thanks.
 
yes. you do need to count the PSU. the PSU does need air to cool it. I use a balanced airflow (pretty much) for better results.
 
Supposedly slightly more exhaust will give you better results as it brings hot air out of teh case faster
 
Originally posted by: RallyMaster
yes. you do need to count the PSU. the PSU does need air to cool it. I use a balanced airflow (pretty much) for better results.
Click to expand...

Thanks. I'm trying to figure a way to cool my 7600GT card down a bit without having to spend any more cash. I think my other temps are pretty good:

A64 3000+ S939 Venice CPU: apprx. 30 idle / apprx. 45 load
Case: apprx. 32 idle / apprx. 48 load
HDD: apprx. 18 idle / apprx. 25 load

My video card idles at apprx. 52 and hits apprx. 68 after playing games for a couple of hours.
 
Originally posted by: 996GT2
Supposedly slightly more exhaust will give you better results as it brings hot air out of teh case faster
Click to expand...

That's what I've been reading on a couple of other sites and I figured I'd try it and see if it made any difference. And I figured I had to count the PSU exhaust fan but I wanted to confirm it.
 
I have a hard time buying into the whole case pressure thing. If there is any pressure, it's so minute it's not even measurable.

There are so many holes in the average case that any chance for a pressure change is easily negated.

I've found that the best method is to just try your fans in different configurations, changing their directions from time to time and see what you get. I've also found that changing their direction only yeilds a difference of a couple degrees at best, but having the standard "Front intake rear exhaust" works best.
 
Everything i've seen says that positive pressure is irrelevant, some people think that it means you get more dust buildup internally but it's not something you can test scientifically with ease. All you have to do is make sure that the PSU fan isn't being overpowered by the exhaust fan so it's working as an intake.

Looking at the airflow is important to fault checking, but positive/negative presssure is rather irrelevant for the most part.
 
My biggest concern about negative case pressure is that it does tend to stall air flow through the power supply, possibly resulting in:
- PS runs warmer than designed temp at load.
- PS runs fans at high speed to compensate, increasing case noise.

Positive case pressure is only inefficient - but it can't hurt your PS. For example, 50CFM front intake fan combined with 35CFM rear vent fan will create positive case pressure and:
- Total through-case air flow will be restricted to only a little more than 35CFM.
- Case noise is increased by the 50CFM fan noise.
- Total case air flow would be greater with only the 50CFM front intake fan, since slower-speed fans in series air flow are flow-restrictors.

I've tried negative case pressure in my case (Single Panaflo M1A 120mm rear exhaust with OCZ 520A PS) with no apparent power supply problems, but not all power supplies perform equally and potential long-term effects bother me. I use balanced Panaflo m1A 120mm fans at 7V for flow of about 50CFM with barely audible fan noise.

Hope this helps!
 
I'm a fan of positive pressure as it does help keep your case clean. But you really do have to do some work to do either a negative or positive pressure system. If you have a lot of open grillework in your case, then it will be very difficult to accomplish either without excessive fan power. So you have to seal your case so that airflow is controlled by the fans and can't get in or out too much at random. On positive pressure, all intakes have to be filtered to realize the dust benefit, so it will require stronger intake fans to compensate.
. The air density in positive pressure will be higher so each cu.ft. of air can hold more heat and thus carry it away when it leaves. A mixing fan would probably be useful to prevent eddies/dead-air pockets in a pos. pressure setup. The actual thruput of air will be mainly controlled by the exhaust fans, thus the ambient temp.
. I favor positive pressure both for the dust abatement and potentially better heat removal efficiency.

.bh.
 
Originally posted by: Bobthelost
...All you have to do is make sure that the PSU fan isn't being overpowered by the exhaust fan so it's working as an intake.
Click to expand...

Amen!

And I tend to run same intake/exhaust not counting the PSU. So I guess I'm for negative pressure. Although I'll tell people I'm pro-positive because EVERYONE forgets to count the PSU fan as exhaust. 😉
 
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