Static pressure isn't how fast the air is moving but rather how hard it's being pushed. Air flow is how fast the air moves. Think voltage vs current, respectively. A high static pressure fan may be able to push air hard, but it's generally not too much air. A high air flow fan might be able to push a lot of air, but if you put something to block it it'll lose all of its airflow. That's why it's recommended to put SP fans on radiators and heat sinks where the idea is to push the air through a restrictive material whereas you put AF fans as case fans because you don't have much in the way and want to put as much air in/out as possible, trading off the not really needed SP for low noise and high airflow.

 

Let's get this straight here. The best and dream fan would have really high static pressure, high airflow, at low revs and low noise. Sadly, such a design doe not exist widely yet, and for those that exist, they cost more.

Now back on topic. Static pressure is not for moving volumes of air, per se. Static pressure is the, say, "ability" to move that given amount of air past a certain restricted distance. i.e. fins/rads. CFM cannot be zero otherwise there will be no air to move.

Now why airflow specified fans you ask? For wider and more airflow for those unrestricted space, pushing air further and wider and more air over your components, such as motherboard chipset, CPU cooler and GPU. Not to mention less noise with no restriction in a perfect circumstance. But you do still need SOME static pressure to get it past, let's say, your case front grille.

Because of how fans are designed, and how fins are angled, static pressure fans and airflow specified fans are designed with their own purpose in mind.

Generally, it's finding that balance and a specified fan for each purpose. There's, sadly, no "one fan to rule them all" IMO.

Will add info when I... finish eating.

Hope this helps?

EDIT: DAMN. Ninja'd.

 

Fans with high static pressure is good at forcing air through tight spaces, like a radiator. They do not nessecarily move the most amount of air, and not always the most silent option.

And faster airflow =/= colder air, it simply moves heat from an object away faster. The air temperature is the same

 

Airflow fans often are good for pushing air straight forward, rather than pushing it outward radially.

Something like a Silverstone air penetrator fan would be better suited to case airflow than something like a Gentle Typhoon, for example.

 

Wow you guys a great, I honestly thought "I'll check back later tonight to see if anyone replied" and not 5 minutes later I have 3 great responses lol.

That explains things for me greatly, thank you!

I'm guessing static pressure fans generally more focused where as air flow fans will provide a wider coverage area ?

 

You are pretty much correct. Think of AF fans as "providing" and SP fans as "utilizing".

 

It's not that simple. Higher static pressure is more "directed". That makes it great for moving air through a radiator or similar, but it may not be what you need for good general airflow in a case.

There is also the matter of noise. Generally speaking, a larger fan will need fewer RPM to move the same amount of air. That often makes them quieter. Smaller fans at higher RPM will often have higher static pressure while moving the same amount of air, but will commonly produce more noise in the process.

A good cooling solution is all about balance. You want it to be efficient and effectively cool your rig, but for many of us, keeping noise to a minimum is essential.

If we take your logic to it's ultimate conclusion, we should be using those 250+ CFM Delta fans. They have higher static pressure than pretty much any non-industrial fans (more than 13 times what a equivalent size bitfenix fan has).
But throw a few of them in your case and you will go deaf.

 

Quote:

Originally Posted by Art Vanelay

Airflow fans often are good for pushing air straight forward, rather than pushing it outward radially.

Something like a Silverstone air penetrator fan would be better suited to case airflow than something like a Gentle Typhoon, for example.

I call nonsense on that. It's NOT TRUE.
Quote:

Originally Posted by Dire Squirrel

It's not that simple. Higher static pressure is more "directed". That makes it great for moving air through a radiator or similar, but it may not be what you need for good general airflow in a case.

There is also the matter of noise. Generally speaking, a larger fan will need fewer RPM to move the same amount of air. That often makes them quieter. Smaller fans at higher RPM will often have higher static pressure while moving the same amount of air, but will commonly produce more noise in the process.

A good cooling solution is all about balance. You want it to be efficient and effectively cool your rig, but for many of us, keeping noise to a minimum is essential.

If we take your logic to it's ultimate conclusion, we should be using those 250+ CFM Delta fans. They have higher static pressure than pretty much any non-industrial fans (more than 13 times what a equivalent size bitfenix fan has).
But throw a few of them in your case and you will go deaf.

1) Bigger fans have lower static pressure
2) Often "airflow fans" are a total flop and has a huge air drop even with dealing with honeycomb mesh grilles

 

Quote:

Originally Posted by DaveLT

1) Bigger fans have lower static pressure
2) Often "airflow fans" are a total flop and has a huge air drop even with dealing with honeycomb mesh grilles

I have said nothing to contradict that.

All other things being equal, larger fans will have lower static pressure while moving the same amount of air. This is a product of lower RPM and the larger surface. Much like the way a smaller nozzle will make your garden hose move the water further and at greater pressure.

Now please add something constructive.

 

Air flow fans do work good as exhaust. If you have good positive pressure they can work very nicely. I do use higher static pressure for intakes because all mine are filtered and most regular case fans just can't move much through a filter.

 

Really when the smoke clears it's a combination of static pressure and amount of air moved.
Problem is:
* 2.2mm H2O rating is the highest point water is pushed up the tube when the fan stops flowing air.
* 80cfm is the amount of air the fan will flow setting on an open bench... or possibly suspended so the surface of bench doesn't lower it's cfm rating.

Neither rating has any real world use by itself. We need to know how much air the fan will move at say... 0.4-1.1mm H20... and let's guess that is 40-60cfm. Problem is that is nothing but a guess.

Here are 2 fans:
* Cougar Vortex PWM = 2.2mm H20 & 70.5cfm
* Gentle Typhoon AP-15 = 2.03mm H2O & 58cfm
Now we could assume that if at 1.02mm H2O the Cougar would flows about 37cfm the AP-15 = 28cfm . Cougar being 9cfm better than AP-15
When really
The plotted data shows Couger flows about 34cfm while AP-15 = 42cfm . AP-15 is 8cfm better than Cougar.

http://martinsliquidlab.org/2013/02/18/why-static-pressure-max-flow-specs-are-poor-measures-of-fan-performance/

So don't rely on fan specs.

Find a good review that tests them on a cooler or radiator.

Because in reality most case intake vents are about as restrictive as coolers.. with grills, doors, HDD cages, cables, etc. After all a simple wire grille will restrict 2-28% depending on fan and who did the testing.
http://www.pugetsystems.com/labs/articles/Effects-of-Grill-Patterns-on-Fan-Performance-Noise-107/
http://www.silverstonetek.com/techtalk_cont.php?tid=wh_chessis&area=en

 

SCIENCE
Dynamic Pressure = Total Pressure - Static Pressure

(via Bernoulli equation)

Dynamic pressure "Q" in martinsliquidlab graph is proportional to air speed "v" (sometimes "u" in aerodynamics) (i.e. q = 1/2 * rho * v^2 , where rho =density of air)

Total pressure aka stagnation pressure is pressure when the fluid stops moving.

This phenomenon is known as the Bernoulli effect. (Velocity inversely proportional to static pressure)

SHORT ANSWER

In short: There's no point in giving up airflow for static pressure if you don't need to , but keep in mind grilles, HDD cages, and filters are flow restrictions.

doyll gave you a good answer, static pressure and airflow numbers are meaningless by themselves

martinsliquidlab piece doyll is referring to: http://martinsliquidlab.org/2013/02/18/why-static-pressure-max-flow-specs-are-poor-measures-of-fan-performance/

Hope that helps

P.S. Air is compressible too but is approximated as incompressible below Mach number of 0.3. Air density also depends on temperature (so mass flow changes but the volume flow "CFM" stays the same).

P.S. #2 I think ASHRAE changed their fan specification method to total pressure.

 

the need for static pressure is directly related to the amount of resistance the air is expected to overcome. with a free flowing environment there is little need for static pressure. however if you need to overcome airflow resistance such as heatsinks, grills, filters, radiators, etc... that's when you need increased static pressure. the higher the resistance to airflow, the higher the need for static pressure.

from an acoustic point of view, a "push" fan produces a quieter acoustic signature then a pull fan. however sometimes a "pull" fan is required to get the job done (such as the fan behind an air filter )

 

Indeed. Good input.

OP:
I do use static pressure fans for ALL applications.

Bottom line: It's better to have it and not need it than need it and not have it.