This is just a quick graphing demonstration of why fan box specs using static pressure and max air flow are generally poor tools in comparing fan performance. Very much like pumps, fans have a pressure vs flow rate relationship that is not at all linear. Some are flat some are curved, some have big bumps and dips and it’s the area between these two points that ultimately matters, not what is at the ends.
For example, let’s compare these two fans using box specs:
Cougar Vortex PWM
Max Airflow = 70.5CFM
Static Pressure = 2.2 mm H20
Gentle Typhoon AP-15
Max Airflow = 58CFM
Static Pressure = .08inwg = 2.03mm H20
Using these specs alone you would assume the Cougar would produce more air flow on a radiator. Both max air flow and max pressure are greater, you can’t go wrong with that can you?
Well, luckily both of these fans do provide P-Q curves(Most do NOT), so I spent some time cropping out their P-Q curves, converting units and overlaying them. First here are their native P-Q curves in different units of coarse making a comparison difficult.
So I brought both into Excel and plotted them out the best I could, here is how that looks:
In addition noise box specs are “Open Air” with no restriction and no adverse “Real World” affects when mounted to a radiator. Since most fans out there don’t bother publishing P-Q curves, you essentially don’t know what there real world performance will be and the noise specs don’t mean much on a radiator either.
So, just goes to show you…don’t rely too much on fan specs, they are not very good measures of real world performance. Just like pumps, it’s the pressure somewhere between these two points that matters in the real world and that isn’t static pressure and it isn’t max air flow, it can only be represented by a full P-Q curve.
And my intent here is not to pick on any one fan. I would like to try some cougar fans out myself considering they are supposedly producing this curve at only 1500RPM, but the curves were available so I wanted to see for myself how the PQ curves compared. Sure enough it produces a very contradicting conclusion vs. looking at only static pressure and max air flow.
Hope this muddy’s the waters for the box spec discussion out there…:)