Do PSU fans steal air from CPU coolers?

[BadOmen]

Greetings

A very general question:

Does the PSU fan steals air from a CPU fan like my Arctic Freezer Pro, which points to the back of the case and it's exactly under the big PSU fan?

Looking carefully, both are pretty close. The PSU fan points down, so it could pretty much interfere in CPU cooling, no?

Is it a significant interference?

Thanks a lot

 

[AnnonUSA]

Airflow entering the box will equal airflow exiting the box. So as long as there are no obstructions in the airflow over the heat sink/cooler, there should be no problem. More airflow = more cooling.

 

[scruffypup]

A very interesting question that I have never seen a review to measure.

Now just breaking it down,...

Your situation you could have more turbulence,... with it creating less airflow through,.. but there are other factors,...

If you have a tower HSF oriented in a way where the "exhaust" of the HSF is pointed towards an intake of a PSU,... it would most likely get a very slight benefit

If you have a tower HSF oriented in a way where the "exhaust" of the HSF is pointed to the back of the case,... and say the fan in the back of the case is weaker (less cfm) than the HS fan pushes,... then you could still get a very slight benefit

If you have a tower HSF oriented in a way where the "exhaust" of the HSF is pointed to the back of the case,... and say the fan in the back of the case is stronger (more cfm) than the HS fan pushes,... then you probably would get no benefit

And so on,... in any of the cases the difference you will see most likely will be less than noticeable (or within margin of error on typical readings)

The one situation I could see it being the biggest difference is if you had a passive heatsink in which there was no fan,... and you did a homemade duct system to draw the air through the passive heatsink directly into the psu fan or vice versa depending on how you have the psu fan spinning of course.

 

[Quiksilver]

I think you typed the question wrong or are mis-understanding it.

Is the PSU stealing air from the CPU? Yes, and no. The PSU is intaking air from the CPU's exhausted air(and any other air in the case).

So if anything it's the CPU cooler that's interfering with air getting to the PSU, not the other way around.

 

[RallyMaster]

>.> I use my PSU as an exhaust for my CPU cooler because I run the Scythe Ninja Rev. B on my Opteron 165 without a fan clipped on it.

 

[Zepper]

Most CPU fans these days flow very little air until they get pretty hot, but they do carry a minor amount of heat away from the CPU area. I think a strong exhaust fan would pull more from the PSU fan than anything else in that area.

.bh.

 

[BonzaiDuck]

Originally posted by: AnnonUSA
Airflow entering the box will equal airflow exiting the box. So as long as there are no obstructions in the airflow over the heat sink/cooler, there should be no problem. More airflow = more cooling.

In a holistic approach to PC building, you would attempt to minimize the number of fans, minimize the amount of noise, and maximize the CFM of airflow. More fans may mean less noise with more airflow. It's not just an easy trade-off, but neither is it a difficult one. If you wanted, you could build an entire case covered with intake fans.

If intake >= exhaust, the only way the "pressurized" approach causes problems would be if hot air continues to mix with cold in the case interior and become "stale" in pockets that don't have enough airflow.

Otherwise, Intake >= Exhaust is better. That being said --

You would only starve the PSU's air intake if intake didn't keep up with exhaust. Further, the newer and better PSUs have an "above-80%" efficiency ratio, and don't generate as much heat.

So even if I attended to and fretted about this problem a couple years ago, it's not a major concern now. It is especially no major concern if you duct the exhaust from the CPU cooler directly to the case-exterior so that the air doesn't mix in the general case interior.

 

[Quiksilver]

Edited my post for clarity.

 

[BadOmen]

The scenario: a HSF blowing towards the back of the case, where an exhaust fan is.

Right above the HSF lies the big intake fan of the PSU. I think this is a pretty common layout nowadays.

The thought that crossed my head: when that big PSU fan pulls air inside the PSU, wouldn't it be capturing some of the air created by the HSF that was supposed to blow straight through the heatsink, thus disrupting the cpu cooling process?

The PSU intakes the air, but due to its proximity to the HSF, it may be intaking the wrong air. Air that was supposed to blow through the heatsink without interfering forces, no?

If I understood your answers (thanks a lot for them, by the way), people shouldn't worry with that, then?


What led me to think of it: my Raidmax case (worst airflow in the market) has its intake fan placed exactly in front of the HSF, interfering with the CPU cooling. I turned it off, actually. Here, check the picture

ttp://i222.photobucket.com/alb...otos/Omenrig_mar08.jpg

 

[BonzaiDuck]

First, consider the pressure (pun!) on power supply designers to keep the noise down. Add to that the greater efficiency and less heat-dissipation of a decent PSU today. PSU fans do not spin fast, and therefore, they do not pull as much air.

My worries a couple years back was that the PSU would be starved by a high-CFM CPU fan. this would not affect CPU cooling, but without enough case intake CFM, the PSU would be starved.

Suppose enough slightly-warm CPU exhaust air IS taken in by the PSU. Then the PSU would only run slightly warmer, but not appreciably.

It behooves anyone, though, to get familiar with what is considered "effective computer-case airflow." You'll find some white-papers, articles and comment through a web search.

It is possible that fan-deployments can conflict and reduce airflow from what is most effective. The goal of ducting components in a case interior is to make all fans work together, directing air mostly on the hot components and exhausting it quickly from the case. With attention paid to "hot components" and using ducts to sequester the airflow I just mentioned, you'd only need intake fans to provide sufficient CFM to feed both the ducts and the PSU.