Discussion Need advice on airflow

[Zombiefruit]

Hey guys,

I'm currently rebuilding my sffpc in a zs-a4 v2 case. The case allows for one bottom-mounted 120mm fan. I'm currently having issues deciding on exactly which setup to go with, and I'd appreciate some help.

I've had to deshroud my 3070 to get it to fit, and I'm limited here to having the noctua fans I've added run in exhaust (due to turbulence noise when running in intake) so that's the one fixed value in the equation. My debate lies in which orientation to put the CPU fan and the bottom fan. I've made some images to show possible layouts. For context, the RAM sticks and PSU seem to create a decent buffer between the CPU and the bottom fan, so I'm wondering if the bottom fan direction is even relevant to the CPU.

Oh, and for reference I'm using a Noctua L12 s1 as the CPU cooler, but with a slim a9x14 fan (all I could fit). Not very powerful and I worry that if set to exhaust I'll see higher temps.

CPU as intake, bottom fan as intake:

In this way I'm wondering if the air from the CPU is pulled out over top of the case and through the vent holes by the GPU suction. The bottom fan as intake is also ideal for the GPU as it's helping the exhaust, not fighting it. The issue here is that the GPU is pulling air in from the top and the CPU fan is trying to expel air the same way. Either the flows will merge as the CPU air is pulled over or I'll have turbulence.

CPU as exhaust, bottom fan as intake:

This is the most balanced approach, but I worry about the CPU temps, and the fact that the bottom fan doesn't really feed the CPU chamber.

Bottom fan exhaust, CPU intake:

This case is probably worst for the GPU since the bottom fan is fighting it. However, I assume it's the best for the CPU, as the case is mostly negative pressure and the CPU fan is the only place that's actively pulling in air (so would get a bit more flow). Not sure how much it'll screw the GPU temps though.

So that's my conundrum. Appreciate any advice!

 

[scatterforce]

Typically, in a sandwich case, you want all case fans as exhaust and GPU / CPU as intake. I've not seen someone experiment in your exact case, but this has been the conclusion for many other builds.

Only the 3080/90 Founders cards with fans on the back change this. In some cases, it's better to have intake under the founders cards than exhaust. With a deshrouded 3070, that won't be the case.

 

[Zombiefruit]

Only the 3080/90 Founders cards with fans on the back change this. In some cases, it's better to have intake under the founders cards than exhaust. With a deshrouded 3070, that won't be the case.

The only issue is that I'm forced to run my GPU in an exhaust config, since the turbulence noise is too great when the fans are running up against the side of the case in intake. Which means that I'm sort of in a weird place versus most other builds I've seen.

I want the bottom fan running in intake to feed the GPU, so I guess my question is which orientation to have the CPU fan in (intake or exhaust).

 

[scatterforce]

I would still do CPU as intake. Your PSU is already pulling air in; if CPU is exhaust, some air will be recycled through your PSU.

Ultimately, the only way to know for sure is to stress test both configurations. No matter which way the CPU fan is oriented, the bottom fan needs to stay as intake for your GPU.

 

[Zombiefruit]

Okay, awesome. I'm gonna put together a little cardboard box setup to see how the airflow is working before I commit and throw the case together. Thanks!