[SOLVED] Is Push-Pull worth it for an AIO?

[WubLyfe]

I've gotten some good feedback on this on Reddit, but I'd like to see what this community thinks as well.

TLDR: Is it worth it to do push/pull on an AIO rad when not using high static pressure fans and the rad is the only case intake?

OP:

Ok, so:

I'll be moving from a Dark Base 700 to a Phanteks P400A this weekend. I think I've got the fan configuration figured out, but I wanted to run it by you all here because I'm not very experienced with radiators. My GPU is on a Kraken X53 with G12 AIO bracket, and CPU will have a Kraken M22 Bequiet Pure Rock. My proposed configuration:

Front:

2x 140mm Deepcool CF140 (64.13 CFM, 1.09 mmH2O)

NZXT Kraken X63 Radiator (280mm)

2x 140mm Bequiet! Silent Wings 3 (59.5 / 101.09 CFM, 1.08 mmH2O)

Top:

2x 120mm Bequiet! Pure wings 2 ( 51.4 / 87 CFM, 1.25 mmH2O)

Rear:

1x 120mm Deepcool CF120 (56.5 CFM, 1.63 mmH2O)

NZXT Kraken M22 Radiator (120mm)



After a great deal of help/advice from u/-UserRemoved-, I am now debating between these two configs:



Front:

2x 140mm Deepcool

X63 Radiator

CPU:

2x 120mm Pure Wings 2

Top:

2x 140mm Silent Wings 3

Rear:

1x 120mm Deepcool



Front:

2x 140mm Deepcool

X63 Radiator

2x 140mm Silent Wings 3

CPU:

1x 120mm Pure Wings 2

Top:

1x 120mm Pure Wings 2

Rear:

1x 120mm Deepcool



Other components:

Ryzen 5 3600 (no OC)

RX 590 (w/ Kraken G12 kit)

MSI B450 Gaming Pro Carbon WiFi

2x 8gb Vengeance 3000

Phanteks P400A



Which of these setups would you go with, and why?

 

[digitalgriffin]

Weird. I'll give it a go with no top exhaust. I wouldn't have even thought to remove that had you not mentioned it.

In general balanced airflow (in and out) is always the best solution. But if you have to pick negative pressure versus (fans sucking out) positive pressurized case (fans pushing in), over pressurizing should be better.

The fan exhaust always has a lower pressure. This is what makes the fan air move from front (high pressure) to rear (low pressure)

Now atmospheric pressure is about 14.7 psi at sea level.

Over pressurize example
[edit] If you over pressurize a case to lets say 14.9 psi, and the fan has .2 psi static pressure increase (generated by fan),

14.9 - 14.7 = 0.2 differential (We need a pressure differential for airflow remember?)

Negative case pressure example
Now lets say you under negative pressure and the inside of the case is 14.6 psi.

Static air outside the case is 14.7 psi.

[edit] (14.6 +.2) - 14.7 = .1 differential. You hardly get airflow because the outside case static pressure outside the case is higher than what the fan can fight effectively.

That said, over pressurization can work against you because it becomes much harder to control where the air flows from point A to B.

 

[Phaaze88]

Yeah, I think what's happened in my situation:
Ever since I installed that hybrid cooler on my 1080Ti, it changed the way air moves in my PC.

 

[tennis2]

Static pressure fans - Visually, these have blades that are comparatively fewer in number and/or wider. They push air through restrictions (radiator) better, but because of their design, don't push as much air VOLUME per rpm as an airflow-optimized fan. They also tend to be a bit noisier at a similar rpm airflow-optimized fan.

Airflow-optimized fans - Visually, these have more/thinner blades than SP fans. They push greater volume of air at similar rpm, but can't push air through restrictions as well. They also tend to be a bit quieter at the same rpm as a static pressure fan.

Radiators are a good example to use because they pose a [comparatively] high airflow resistance. Any air that doesn't go through the rad (because the fan can't produce enough SP) gets "splashed" back. You can actually feel this on your hand (or hold a piece of tissue in front of the fan). However, that air that's splashing back has already touched the rad fins, so it's heated. And where do you think the fan is pulling air from? Yes, the mass of air right in front of it, which includes the "splashed" air.

Digitalgriffin had a good explanation of the scientific benefits of push-pull. Basically the pull fan is creating a vacuum inside the rad, so that the push fan has an easier time getting air in.

Also, there's a whole range of airflow and SP optimizations in the fan market. Let's oversimplify the market as such:

• Static pressure fans
• Airflow-optimized fans
• 50/50 of SP and airflow

Also fan quality muddies the waters further. A SP fan from manufacturer A could very easily be quieter at the same rpm (and maybe even move more air) as an airflow fan from manufacturer B.....

There's always a give-and-take depending on the static pressure a fan needs to overcome. Naturally, one would think "oh, I put airflow fans in my case, and SP fans on my CPU heatsink" but it's not that simple.

• Generally radiators have more densely packed fins than a tower-style CPU heatsink. So naturally, you'll want to use a MORE static pressure optimized fan on a rad than a tower. But the tower still has more resistance than a fan blowing though an open case, so a 50/50 fan may be the best here.
• For cases, you'd think that you're going airflow-optimized fans all day, but some cases pose a greater airflow restriction (ie tempered glass front panel and a tiny vent at the bottom where a 50/50 or SP fan would be best) than others (ie mesh front panel where an airflow or 50/50 fan works best).

This obviously isn't a black-and-white problem.....