Question CPU and GPU AIO radiator fan airflow direction ?

[fcar1999ta]

I am in the process of installing an Alphacool AIO GPU cooler, and I noticed that the vendor that built the PC has the CPU AIO fans pushing inside case air out. I would think that you would want the AIO fans pulling cool outside air in, then using the case fans to expel the combined hot air. Am I actually completely backwards in my thinking?

 

[Ralston18]

I think there are two primary considerations:

1) You want to take advantage of the fact that hot/warm air naturally flowing upwards. Convection.

2) You want the outward airflow rates to exceed inward airflows to avoid a balloon effect that slows overall air flow. Possibly reducing the ability of airflows to carry away heat.

That leads to providing some understanding of the current fans, airflow directions, airflow rates, and fan case locations.

I suggest, if possible, that you take a couple of photographs of case and fans.

Indicate the airflow directions and fan airflow ratings.

Post the photographs and accompanying airflow information herein via imgur (www.imgur.com).

 

[fcar1999ta]

There was more coming in than going out.
In = 3 bottom and 4 side.
Out = 2 back and 3 top (CPU AIO).

I am thinking:
In = 3 bottom (GPU AIO) and 3 top (CPU AIO).
Out = 4 side and 2 back

All of the fans are the same. If you factor in filters, then the air out would slightly exceed the air in

 

[CountMike]

There was more coming in than going out.
In = 3 bottom and 4 side.
Out = 2 back and 3 top (CPU AIO).

I am thinking:
In = 3 bottom (GPU AIO) and 3 top (CPU AIO).
Out = 4 side and 2 back

All of the fans are the same. If you factor in filters, then the air out would slightly exceed the air in

For better CPU/GPU cooling, cold air intake is preferable. Ideally it would be best to have intake and exhaust air flow matched, but some imbalance may have positive effect, More intake results in positive pressure with reduced dust collection, better coverage of other components and more cooler air coming in. Negative pressure when exhaust airflow is dominant results in faster air exchange in the case.
Altogether all that applies only when fans are running full speed or all have same airflow but each fan or set of fans is usually separately adjusted according to each component's thermal sensor and RPM curve so as whole it's variable form moment to moment.
PS. Forget about natural convection, in such small space and height difference it's negligible and even small fans are stronger influence. It takes tall chimney or much higher space to have any effect.

 

[fcar1999ta]

I think having the 3 CPU and 3 GPU AIO fans pulling and the other 6 pushing is the best configuration. Plus, I think I can program the BIOs so that intake and exhaust fans are matched.

Thanks for the help!

 

[Paperdoc]

I agree fully with items by CountMike above. I do wonder how you plan to balance having all six rad fans as INtakes. Typically that would require at least five exhaust fans to balance the air flow capacity to achieve a small positive pressure inside the case.

You cannot actually predict the air flow balance simply from fan count and "fan curve" settings. And doing that over all normal workloads (and heat generation scenarios) takes some measurement and experimentation. You need to start by connecting the intake fans as one or two groups, and the exhaust fans as a separate group on a header. Then you can set up custom "fan curves" for each fan group for balance. HOW to get a good handle on the air flow (and internal small pressure) over several workloads is done best with a smoke tracer technique. For details, see the third- and second-last paragraphs of my post of Nov30/23 in this thread

https://forums.tomshardware.com/threads/top-case-fans-realization.3829392/#post-23150166