TOP & BOTTOM FAN FLIP MIGHT BE GENIOUS

[AISTHESIS]

I was told more fans in than out pushes dust out of tight areas (positive pressure). Would negative pressure pull dust out of tight areas just as well? Sacrifice flow for pressure? Negative pressure means less volume and should equal less dust but I think what you pull in is your volume of dust despite current case volume.

Everyone runs the bottom fan in because of gravity but there is so much airflow in the case gravity of denser and lighter air is almost irrelevant I think. Also I think the bottom is at risk for pulling in dust. I am using nice fan screens so I am more curious than concerned.

Currently my CPU runs 100f degrees max and GPU 155f max. My goal is extending life but I have no complaints of temps. I am adding and moving fans, check this out.

Fan locations:
-low and mid of front
-top of rear
-center of bottom
-left and mid of case top

Case is large and roomy.
Hard Drive is bottom right.
Power supply is bottom left.
Mother board is towards top left corner.
GPU must move - it covers the PCI-E for the sound card. S-card ribbon not here yet.
CPU heat sink is centered between the top fans.
No other components. Front drive slots are now mesh. (maybe bad for flow rate)

Now CPU: Currently I have the top fan (centered) blowing fresh air down before the CPU fan. so not to rob it of pressure and fresh air. The other top fan (other side of CPU sink) is pulling hot air out of the case just like the rear fan. This is giving me good temps and grate flow through the CPU heat sink. There is no collecting of warm air in the top of the case.

I have two front fans pulling fresh air in and one rear blowing out.

BIG QUESTION: The bottom fan? Do I blow in and have 4 in fans and 2 out fans with possitive pressure? Do I have it blow out for more total case flow? Do I follow the masses and flip the top fan to blow out in fear of gravity/densisty? I don't have a fan for the bottom yet, but soon. What do you think? I think the top fan being intake is helping greatly, at idle my CPU is 66f degrees (room temp) and I think the bottom fan out will be best overall flow (3 in 3 out). I will be doing tests soon and will post the results of this odd setup and temps. If you try some top and bottom fan flipping post your temps.

[Chompman]

You want the bottom front fans blowing in and the top ones blowing out.

You do this for 2 reasons and they are heat rises and this forces the warm air out the back / top and the cool air blown in from the front will be cooler and it gets sucked past the gpu and cpu cooling them while it heats up and exhausts the back / top.

If you do opposite it causes the air being blown in from the top to get trapped more and heat up while the bottom fans are doing nothing but exhausting cooler air from the cases normal case holes from the back and bottom of the case.

You could try both and check the temperatures but unless your case is very odd it should work the normal way with front intakes on bottom and exhaust in back top and rear.

[Washell]

Negative pressure means that the air pressure inside the case is lower than the room. Since pressure wants to equalize, your case will start sucking in air and dust through every hole, crack and opening available, which means your nice fan screens are completely bypassed.

Positive pressure means that the air pressure inside the case is higher than the room. This means that the air will push out through every hole, crack and opening available, which means that the only air that gets in the case, has passed through your fan screens.

It has nothing to do with pushing dust out of tight areas, you just listened to an idiot who heard something but didn't grasp the reason why and invented his own.

Without fans, the natural flow of air inside the case is that the heat from the components rises out the top, and cold air gets sucked in at the bottom by convection. Reversing this natural flow means your fans will have to spin harder (more noise/power use) to get the same results. Working with the natural flow is quieter and more efficient, and dust getting sucked in from the bottom is easily solved with a filter, or putting the case two foot above floor level.

[Midnight Fawn]

YouTube™ Video: Case Flow and Pressure Demonstration - How to balance airflow 

Views: 2,144,685

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[AISTHESIS]

WASHELL, great explaination, thanks for the education on pressure.
SCOTTISH TABLET, thanks for the video, perfect, watching now.
OTHER 2, thanks for the info and how changes worked for you.

I understand density and convection well. Using tape and thread or ultra light ribbon you can see the flow pattern in a case. with the top (centered) fan blowing down that fresh air is being sucked directly into the cpu fan and there is no heat pooling at the top. With both top fans exhausting the cpu fan has reduced flow and temp rises 15f degrees. I cannot top exhaust on the right side of the cpu. I have tried multiple configurations with the 5 fans and having front intake, rear exhaust, and 1 top intake 1 top exhaust gives the lowest temps. That is 3 in 2 out with possitive pressure. Using thread, temp gun, and Speccy monitoring this is actually best for my case with 5 fans so far. Can't wait to get fan 6.

[AISTHESIS]

Great video, answers lots of questions. He is using exhaust fans at the bottom side of the case. Yes heat rises but in some cases you force the flow where you need it and even against the help of convection.

[Dr.Shadowds 🐉]

Watch both these videos, as one explain, and the other shows with the fog machine.

YouTube™ Video: Positive vs Negative Air Pressure as Fast As Possible 

Views: 1,534,069

Which is better within a computer case; positive or negative airflow? It's an age old question, but is there one correct answer?

YouTube™ Video: Computer Case Airflow - What is Positive and Negative Pressure? 

Views: 2,045,295

Ever wonder what positive and negative air pressure in your case means? Well, Anthony and Jack came up with a way to show you exactly what happens inside.