I am building a 1680 atm and have decided to go with two 180mm fans, one top, one bottom, both pushing into the cavity.
I believe this will yield a positive pressure that will flow over the rad fins & out, taking heat to the outside.

If you are going with the fan rails & 140mm fans, I would have all (as many as you install) pushing air over the rads to the outside, so the heat doesn't build up inside.

That's my thinking on the subject

Are you still going to install the two Phobya 180mm x 32mm G-Silent 18 fans you mentioned previously?

The Phobya 180mm x 32mm G-Silent 18 top fan you specified pushes 169 m³/h.
Each Noctua NF-A14 PWM pushes 115,5 m³/h at the Low Noise level, for a total of 1386 m³/h.

If you split that requirement 50/50 between top & bottom for air supply, each end will need to pass 693 m³/h.

I believe the 180mm top fan will be more a hindrance than an aid.
It may be better to keep both top and bottom open so the 140mm fans can draw what they need.

Quoted from "InfoSeeker"

The Phobya 180mm x 32mm G-Silent 18 top fan you specified pushes 169 m³/h.
Each Noctua NF-A14 PWM pushes 115,5 m³/h at the Low Noise level, for a total of 1386 m³/h.

If you split that requirement 50/50 between top & bottom for air supply, each end will need to pass 693 m³/h.

I believe the 180mm top fan will be more a hindrance than an aid.
It may be better to keep both top and bottom open so the 140mm fans can draw what they need.

Those figures are free flowing maximum figures and bear no resemblance to results when used on a radiator, or when supplying air to a negative pressure environment. Put simply its almost impossible for the large intake fans to be a hindrance .. it just doesn't work that way. The airflow generated by the rad fans just supercharges the flow through the large fans and vice versa. The large fan is moving air into a negative pressure environment which automatically means they generate more flow than they would in a static air free flow environment.

Fans, just like pumps, don't hold flow rate at their own specific level. If they did then push pull would work no better than push only and one pump would be no better than two. All they do is provide pressure and flow rate can vary enormously.

Hello Jakus,

This is an interesting topic, and not being a Sheldon Cooper, I was working from what I call common sense physics. Let me explain my thought process.

I agree the published performance of the fans reflects free flowing conditions, and are not accurate for real world application. But relativity remains... what I mean is, if fan 1's airflow specification has double the capacity of fan 2's airflow specification, in real world situations fan 1 would still have the greater output.

You state:

Quoted

The airflow generated by the rad fans just supercharges the flow through the large fans and vice versa. The large fan is moving air into a negative pressure environment which automatically means they generate more flow than they would in a static air free flow environment.

It's the "vice versa" part I question.

As you say, the Rad fans would create a negative pressure inside the radiator, which creates a greater pressure delta across the fan at the top, in the direction of flow, and will consequently increase the airflow through it. But conversely, the negative pressure inside the radiator will cause a greater pressure delta across the rad fans, against the direction of flow, and would have a detrimental effect on output.

Push-Pull works because the push fan increases (supercharges) the inlet to the pull fan. If the push fan were not able to at least meet the inlet requirement of the pull fan, i.e. be restrictive, the setup would not work. The same is true for dual pumps, If the output of the first pump did not exceed the input/supply need of the second pump, there would be a loss to the output of the setup.

The negative impact may not be too noticeable in the proposed gigant setup because the bottom is still open and will make up the difference. But I believe the top fan will not be a positive contributor to the overall scheme.