Putting PSU facing CPU means the PSU has to absorb air from the inside of the case, and I was concerned that the CPU fan might fight with the PSU fan for air. This turned out to be a non-issue, but it reminds me of another approach – reverse the CPU fan. This setup was mentioned in some forum, but I didn’t take it seriously. On a second thought I find it a brilliant idea. I can’t believe I missed it.

The setup is quite intuitive when you think about it, but you really have to think outside the box. Normally the CPU fan blows toward CPU, which forms an opposite airflow to the PSU fan if you’re using a case like the Lian Li PC-Q07. But on the other hand, this also means that if you reverse the CPU fan it would blow in the same direction as the PSU fan. Problem solved! Air flow should be better and system will be cooler. I did a quick test to validate my guessing.

1. CPU Fan Blowing toward CPU (normal), 2000 rpm

Fan Blowing CPU Max RPM

2. CPU Fan Blowing toward PSU (reverse), 1260 rpmFan Blowing PSU 1260 RPM

3. CPU Fan Blowing toward PSU (reverse), 2000 rpmFan Blowing PSU Max RPM

[table]

Fan Facing Fan Speed (rpm) Max CPU Temp. (Celcius)
PSU 2000 58
PSU 1260 64
CPU 2000 64

I’m looking at the maximum CPU temperature during a wPrime 1024M run which fully loads the four threads of i3-530 for about 10 minutes. When the fan is running full speed at 2000 rpm (1st and 3rd screenshot), the maximum temperature is 5 degrees lower. The 2nd screenshot shows for the system with CPU fan blowing toward PSU to achieve the same max temperature as the system with CPU fan blowing toward CPU, the fan needs to run at only 1260 rpm. That is a big reduction in noise. Slowing it down to 1260 rpm the noise becomes nearly unrecognizable as it’s overwhelmed by other noisy components such as the PSU fan and the GPU fan. So, this setup is really a perfect balance between noise and temperature, and I have been using it in my PC-Q07 ever since.

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