you have a CPU fan pushing max 94cfm - but intake/exhaust is only 45cfm

[flexy]

i was wondering...

My oldfashioned case has one intake 80mm w/ 45cfm and one exhaust w/ 45cfm as well as a PSU with two fans (one at bottom, sucking from CPU area)

I mount a 120mm on my XP-120 which is capable to push 94cfm at maximum setting.

In other words: The CPU fan is pushing more than the amount of fresh entering the case !

What do i do ?

Would a case with an airduct (on the side) be much better ?

 

[akseli]

Originally posted by: flexy
i was wondering...

My oldfashioned case has one intake 80mm w/ 45cfm and one exhaust w/ 45cfm as well as a PSU with two fans (one at bottom, sucking from CPU area)

I mount a 120mm on my XP-120 which is capable to push 94cfm at maximum setting.

In other words: The CPU fan is pushing more than the amount of fresh entering the case !

What do i do ?

Would a case with an airduct (on the side) be much better ?

I don't think that really matters, only thing is that you'll probably have negative pressure inside your case causing air to get sucked in through all the cracks in your case. Only option would be to build a duct from the 120mm fan direct to a intake hole which you'd cut into the side of the case ... but dunno, what are you running in that case ?

 

[Insomniak]

Negative pressure. Most cases exhaust more than they take in. Hell, the Cooler Master Centurion is DESIGNED around the idea of negative pressure, hence it's offset exhaust and intake fan sizes, and all mesh front bezel.

It's really a rather elegant design, actually. Efficient.

 

[Tiamat]

I have found the negative air pressure works better for cooling since the rear fan draws air from the most effective locations (cooler air) without as much turbulence.

The problem wifh your set up is that your XP120 will not perform as nicely as you want because it is recycling its own air. If you were to have the fan suck off of the XP120 and blow into some sort of duct that leads directly out of your case, your cooling would probably get much better.

 

[Jeff7]

In this case, as the CPU fan isn't really interacting with the through-case airflow, it shouldn't really be considered in the equation of intake vs exhaust. It will only cause turbulence as far as that system is concerned.

I think that having positive pressure is better in terms of dust buildup - with negative pressure, air (and dust) will get sucked in wherever it can find a way. With positive pressure, you can put a dust filter over the intake fan(s), thus helping confine the dust to those areas. My Antec SLK3700's have one intake and two exhaust (1 exhaust, 1 PSU). I use a fanbus in each to run the rear exhaust slower than the intake on the front; all but the finest dust builds up on the removable filter for easy cleaning.

The problem wifh your set up is that your XP120 will not perform as nicely as you want because it is recycling its own air. If you were to have the fan suck off of the XP120 and blow into some sort of duct that leads directly out of your case, your cooling would probably get much better.

Or a filtered duct going from outside of the case onto the CPU. That way, you get positive pressure and the CPU gets fresh air.