Build Advice FAN Setup for new PC

[lolokaa]

Hi all,

I am planning on building a new PC this year when Navi/Ryzen 3000 comes out. The build is decided for the most part, but I am looking to optimize fan setup for my case of choice.

The case will be Fractal Design Meshify C - TG, and it has several filters; front, bottom, top. For this reason I am considering going 2x 140mm airflow fans with decent SP as front intake, 1x SP 120mm as bottom intake, 1x AF 120mm rear exhaust and 2x 120mm OR 2x 140mm top exhausts.

Fans will be all Noctua.

With 2x 120mm as top exhaust, the setup totals 373.8 intake airflow with a 294.7 exhaust airflow.
This creates the desired positive pressure.

INTAKE

2x 140mm front (AF) = 280.4 airflow 4.16 static pressure (NF-A14 PWM chromax 2x 140.2/2.08)
1x 120m bottom (SP) = 93.4 airflow 2.61 static pressure (NF-F12 PWM chromax 93.4/2.61)
= 373.8 airflow IN 6.77 static pressure IN

EXHAUST

1x 120mm rear (AF) = 107.5 airflow 1.19 static pressure (NF-S12A PWM chromax 107.5/1.19)
2x 120mm top fan (SP)= 187.2 airflow 5.22 static pressure (NF-F12 PWM chromax 2x 93.4/2.61)
= 294.7 airflow OUT 6.41 static pressure OUT

What I'm wondering is whether I should swap out the 2x 120mm top exhausts with 2x 140mm (2x 140.2/2.08) instead of (2x 93.4/2.61) which would lead to a total exhaust airflow of 387,9 instead, resulting in a negative pressure. Is this correct?
Or maybe just swap out 1, which would lead to a total of 355,2 exhaust airflow. 1x 120mm/1x 140mm top exhausts, and positive pressure remains.

What are your thoughts? Apologies for the messy post.

 

[AllanGH]

My only input to this is that you should avoid creating negative pressure conditions in any computer case. Doing so instigates unfiltered air influx through any opening in the case, multiplying your dust accumulation problems.

Positive case pressure, created by the inflow of filtered air, produces a situation wherein the air will flow out of those same openings but, since the air is filtered, your problems with dust fouling things like USB and audio connectors is drastically reduced.

I live in a very dusty environment and, believe me, I have to deal with this issue all the time. You want at least enough positive case pressure to keep air flowing out of those nooks and crannies, and you want the air flowing into the case to be filtered.

 

[lolokaa]

Hi all,

I'm building a new PC, case will be Fractal Design Meshify C - TG. It has several filters; front (2x 140mm), bottom (1x120mm), top (2x 120/140mm).

What I'm wondering is whether I want positive or negative pressure inside the case. I did some numbers:

INTAKE
2x 140mm front (AF) = 280.4 airflow 4.16 sp (NF-A14 PWM chromax x2 140.2/2.08)
1x 120m bottom (SP) = 93.4 airflow 2.61 sp (NF-F12 PWM chromax 1x 93.4/2.61)
= 373.8 airflow IN 6.77 static pressure IN
EXHAUST
2x 140mm top (AF) = 280.4 airflow 4.16 sp (NF-A14 PWM chromax x2 140.2/2.08)
1x 120mm rear (AF) = 107.5 airflow 1.19 sp (NF-S12A PWM chromax 1x 107.5/1.19)
= 387.9 airflow OUT 5.35 static pressure OUT

With 2x 140mm top exhausts the total exhaust airflow(387.9) exceeds the intake airflow(373.8).

I know negative pressure = better cooling, positive pressure = reduced dust, but are there any other benefits/downsides to positive/negative pressure?
Should I swap out the 140mm tops with 2x 120mm instead(which leads to 294.3 total) or maybe 1x 140mm/1x 120mm top for positive pressure? Those 120mm also offer slightly better static pressure through the top filters.

Apologies the messy post but I want to make sure I get this right.

 

[lolokaa]

My only input to this is that you should avoid creating negative pressure conditions in any computer case. Doing so instigates unfiltered air influx through any opening in the case, multiplying your dust accumulation problems.

Positive case pressure, created by the inflow of filtered air, produces a situation wherein the air will flow out of those same openings but, since the air is filtered, your problems with dust fouling things like USB and audio connectors is drastically reduced.

I live in a very dusty environment and, believe me, I have to deal with this issue all the time. You want at least enough positive case pressure to keep air flowing out of those nooks and crannies, and you want the air flowing into the case to be filtered.

So I might benefit from keeping the intake airflow 373.8 and have the exhaust airflow stay at 294.7 utilizing 2x 120mm top exhausts instead of 2x 140mm tops which would result in a 387.9 total exhaust?

 

[AllanGH]

Or go with the 140s and run them slower....either way, just keep your intake CFM higher than your exhaust CFM, and you're going to have less dusting issues.

 

[lolokaa]

Or go with the 140s and run them slower....either way, just keep your intake CFM higher than your exhaust CFM, and you're going to have less dusting issues.

Am I calculating the airflow intake/exhaust right? Add all intake fans for their CFM total and compare it against total exhaust CFM? No need to account for filtering or anything?

 

[AllanGH]

If you bump your intake CFM 20% to 30% over your exhaust CFM, you will compensate for filter resistance and loading over time....just as a quick rule of thumb.

 

[lolokaa]

That means I'm hitting the sweet spot with that set up then

INTAKE
140mm 2x 140.2 280.4
120mm 1x 102.1 = 382.5

EXHAUST
120mm 2x 102.1 204.2
120mm 1x 107.5 = 311.7

That is about 20%~ more in than out.

2x NF-A14, 1x NF-A12x25 intake
1x NF-S12A, 2x NF-A12x25 exhaust

 

[AllanGH]

Sounds like it.....just keep up on your intake filters.

I got lazy on mine, and I really didn't care for the clean-up I had to do when the case went negative pressure for a few months. 🙄