Haha, I get that it’s a little unorthodox. My simple thinking led me to this. Hot air rises, and the NH-D15 is open. So instead of fan’s pushing air in, and fan’s sucking air out, I figured that this simple sucking air out would be sufficient. And it does, even without blowing the fan’s at max speed. On the contrary, I have set the fan’s on a very silent curve. The fan inside and above the Noctua are set to the cpu temp, the other fan to a much warmer sensor. It works, but I would believe you if you said that this is negative for the gpu. The case is a Fractal Design Meshify C.
OK. So you have a very open case and you're doing a chimney, cold air being sucked at the bottom and rising to exhaust at the top. It seems to work, at least because the NH-D15 is a very big cooler for a not-so-hot CPU.
But the bottom radiator has to draw air from the sides because it is blocked by the GPU, while the top radiator has some air vaguely pushed from the bottom and sucked from the ceiling fans; that's probably not very efficient. And what's happening with the GPU? If it were a workstation-style blower, it would draw its own cool air from the bottom and exhaust hot air through the slot; but a consumer-style double or triple fan just moves air
within the case—which means that the CPU cooler actually sucks in warm air raising from the GPU.
This was the original setup. But here I was blowing the NH-D15 air to a much smaller fan. This seemed counter productive to me. And 5 fans instead of 3 now.
What seems counter-productive to me here is the front top fan, taking out cold air which should aim for the CPU.
The 120mm fan acting as exhaust for a 140mm in the cooler can somewhat match by spinning a bit faster.
And in the original setting, the
front bottom fan was sending cold air the way of the Z390 chipset (it needs some airflow!) and the GPU.
I'm no cooling expert, but I would suggest a variant of the original setting with the
top closed and the bottom front fan moved to the lowest possible position. Simple front-to-back flows:
In the lower half, the front fan pushes air towards the chipset and the GPU fans.
In the upper half, the back fan exhausts warm air from the cooler; you may have an upper front fan expressly pushing cold air towards the cooler, or let the cooler draw its own cold air—it's pretty open. But no "short circuit" from an open top.
3 or 4 fans, and hopefully generally lower temperatures than with the present "chimney" but only experiment could tell.
