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Question regarding airflow....

SparkyJJO

SparkyJJO

Lifer
I've heard 2 ways to do case cooling, which one is really best?
1) negative internal pressure where the CFM out is higher than the CFM in. Theory behind it is that way there is no "stale" air in there, fresh air is constantly being drawn in.

2) positive internal pressure, exact opposite of #1, with more CFM in than out.

Which is best? I'm trying to get optimal cooling here.
 
I would like to know too..

and is there such a thing as; too much air flow is a bad thing? Where the exhaust air is cool, should you turn the fan down? Maybe too high of speed isn't allowing a good cooling flow?? Where it 's just sucking the air straight on through, and not allowing to cool the cpu/board?


 
Originally posted by: Jase03
I would like to know too..

and is there such a thing as; too much air flow is a bad thing?
Click to expand...
More noise and dust is all I can think of. The electricity cost is negligible.
 
There's a potential problem of PS overheating due to negative case pressure.

Most power supplies have internal fan(s) designed to draw air from the case and exhaust it out the back. PS fans are usually low-flow fans, with flow-rates much lower than normal case vent fans. Excessive negative case air pressure can stall air flow through the PS.

This can result in overheating the PS and/or thermal-controlled PS fans spin up to full speed to attempt to compensate for the heat in the PS, increasing case noise.

Also, unfiltered dust tends to be sucked into the case through every opening.

Best ventilation efficiency is with matched flow-rate intake and exhaust fans. For two fans in series flow path, the actual flow rate for unmatched fans will be close to the flow rate of the lower-flow fan.

Hope this helps!
 
Dunkster is right, if not wording things a bit complexly. I usually will match my intake and exhast fans as best as possible then turn the exhaust fans lower with whatever fan controller I happen to be using, thus creating a mild positive pressure. I can vouch that a negatively pressurized(or positively vacumned) case has a lot of dust problem and temperatures are minimally if even noticably affected. Your best bet it getting the flow direction as close to perfect as possible, and in the process usually your pressure gets pretty close to level. The best way I've found to check flow directionailty is to set the case up with all the fans and your fan controller, set them where you find them audibly acceptable and either blow smoke or fog into the case and see where it goes. Of course this only works with a case with a window but, it shows you the dead spots in your case and where the best airflow is, then you can adjust accordingly.
 
OK right now I have a 140mm fan in the back that is rated at 55CFM and a 120mm in the front that is rated at 38CFM. I don't know how much the PSU does but the 120mm fan in there typically spins at about 800RPM, I'm guessing 20-30CFM depending on what temp the PSU is at.

Right now airflow is somewhat of a mess in my case because my case has a mesh instead of a window. Kind of odd I know, and it allows dust in very well but also disrupts the "wind tunnel" effect in the computer (also lets the noise out). I'm going to replace it with an acrylic window here at some point when I get the time.

I have a spot to put a 80mm fan on the right side near the front (to blow across the HD, they mount perpendicular to the other bays) so would it be a good idea to put a quiet fan there to try and even out the airflow? Or, when I go to change the mesh to a window, put a side fan that blows in towards the graphics card? Or, slice a hole in the bottom of the case and put an intake fan down there?

Thanks for your input so far!
 
I looked at that SVC cooling guide, and I've done a lot of business with SVC. But I disagree about the balance between intake and exhaust.

The caveats to advantage with a slightly pressurized case might be motherboard ducting, and a case that is relatively well-sealed so that the only place for air to exhaust is through the exhaust fan port and the PSU vents and fans.

Under those conditions, I'd opt for a pressurized case.

For the motherboard ducting, the ideal arrangement has the intake fans feeding the CPU fan (blowing down on the HS base and mobo), with the pressure leaking some air through the duct seams and across components like memory modules. This, in turn, feeds the exhaust fan(s). Thus, a serial augmentation of airflow. This departs from other conventional wisdom about putting one fan on top of another, for instance, with a case-panel-mounted blow-hole intake fan forcing air onto the CPU fan -- the benefits there are marginal. But in the pressurized case, the intake case pressure forces air through the CPU fan, which pressurizes the duct somewhat, augmenting airflow to the exhaust fan.

There should be enough pressure in such a system to avoid starving the PSU -- a point that was brought forward earlier in this thread.
 
Case side-vent provide a side-to-exhaust air flow path that usually results in reduced front-intake air flow - resulting in hot hard drive temps. Powered side-vent worsen the problem and add noise.

Traditional Front-to-back air flow path is still best for uniform cooling of all components.

My recommendation:
- Tape of the side vent.
- Replace the front 120mm fan with a higher flow rate fan.
- Check the case fan grills - remove if they're restrictive.
- Use low-restriction input air filters and clean the filter regularly.

Hope this helps!
 
Originally posted by: dunkster
Case side-vent provide a side-to-exhaust air flow path that usually results in reduced front-intake air flow - resulting in hot hard drive temps. Powered side-vent worsen the problem and add noise.

Traditional Front-to-back air flow path is still best for uniform cooling of all components.

My recommendation:
- Tape of the side vent.
- Replace the front 120mm fan with a higher flow rate fan.
- Check the case fan grills - remove if they're restrictive.
- Use low-restriction input air filters and clean the filter regularly.

Hope this helps!
Click to expand...

OK When I change the side mesh to a window I won't put any fan/vent holes in it. That side mesh I know is messing up the general airflow because there was a film of dust on the outside of it from air being drawn through it.

I did check the built-in case fan grills and they were very restrictive so I removed both the front and rear grills and put a wire ring grill in the back. I'm serious, the airflow out of that rear fan doubled after doing that.

What filters would you recommend? I don't think that I'm going to change the front fan but there is room to add an 80mm fan up there too so I think I'll do that to help increase the intake CFM, I have a whole bunch of 80mm fans lying around.
 
My favorite fan filters to date are these. They work quite well, don't restrict much and you can independantly remove the filter for cleaning without having to remove the fan, makes life MUCH easier if you're cleaning them as often as you should be.

Also, adding an 80mm fan will help with airflow, the only disadvantage to that is noise, replacing the 120mm with a good quality aftermarket can render you more airflow and the same db whereas adding an 80mm fan will increase both airflow and noise.

Lastly, if you're not going to be adding that window very soon, a piece of cardboard with some tape in each corner will solve the airlfow problems it is causing as well as a bit of noise cancelation.
 
I do have an aftermarket fan in the front, the aerocool turbine 120mm. I have some really quiet 80mm fans which is what I thought of using.

Thanks for the link to the filters - tho your link doesn't work, an L is missing in the code 😉 😛
 
yeah, I've been here long enough I just recently realized there was a link button that auto parses it, I prefer typing it out anyways though.
 
The best general filter media I've found (I think I read about this in an old spcr article by Bluefront) is pleated (accordion-fold) furnace filter media. Characteristics:
- Folded to increase surface area.
- About 1" thick, due to folding - takes some creativity to mount it.
- Excellent dust-trapping.
- Very low flow restriction - same temps as removing filter.

Walmart has this filter media in 'Arm & Hammer' brand. Just cut out the size you need to cover your intake.

Hope this helps!
 
Great info here, I had to jump in with some questions regarding my setup. Had some high temps as of late, summer and all.
Ordered a Arctic Cooling ACFZP64 Freezer 64 Pro for the CPU, and was thinking of also getting an Arctic Cooling NV Silencer 5 Rev. 3 VGA Cooler as well.

I have a Sonata II case and the intake port has HD bays/frame blocking the air flow. I have one 120mm fan installed where the mount is on the left side of the bays, thinking of adding a 2nd intake fan to increase air flow, tilted upwards toward the other intake fan Fan layout

Also thought about cutting a few bays out to unblock the fan to allow better air too, really rather not... or changing to a fan filter style? and removing the case filter. The stock filter in more plastic than screen.

Any advise on this setup? bad or good?

TIA!
 
Just add the additional fan and don't bother with the cutting or odd mountings until you see the results. You'd be surprised how much it will help!
 
I think the generally accepted rule here is to have a slightly positive pressure to avoid dust build up, or to have them as equal as possible.

But some people swear by negative pressure.
 
Those that swear by negative pressure are proof that you can get apes to read Greek philosphy by sign language, but they simply don't comprehend the material! That low temperature they are reading is yes, because of the lower pressure it does read a lower number in temperature, but lack of air volume IN THE CASE where it matters means less BTU's transferred per minute and a higher actual internal working temperature for the parts in question.

Negative pressure gives you that warm feeling you get when you pee your pants in the pool, but does nothing to help anything clock further or run quieter or more dependably or longer.
 
Originally posted by: Luckyboy1
Negative pressure gives you that warm feeling you get when you pee your pants in the pool, but does nothing to help anything clock further or run quieter or more dependably or longer.
Click to expand...

that is damn near sig worthy!
 
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