Fans: Static Pressure vs. Airflow?

GoogalyMoogaly

GoogalyMoogaly

GoogalyMoogaly

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Hi guys,

after talking with some mates at work about fans to cool heatsinks and radiators I got to thinking (always dangerous and often dull!).
I believe I'm right in thinking that to cool a heatsink or rad you want a fan with good static pressure? But surely Airflow comes into it too?

Lets suppose you're cooling a radiator in a push config.
Are you better getting a fan that has a higher static pressure even if it's got quite a lot less airflow?

Here are 4 fans with the values pulled from the manufacturer's website (these may be exaggerated but hopefully they all exaggerated by the same amount):

Scythe - Gentle Typhoon (1,450)
Max RPM: 1450
Airflow: 85 m³/h
Static Pressure: 1.3 mm H2O (?, converting 0.051 in mmH20 to mm (from random site on internet))
Noise: 21 dB

Noctua - NF-P12
Max RPM: 1300
Airflow: 92.3 m³/h
Static Pressure: 1.68 mm H2O
Noise: 19.8 dB

Akasa - Apache Black
Max RPM: 1300
Airflow: 97.74 m³/h
Static Pressure: 2.64 mm H2O
Noise: 16.05 dB

Enermax - Apollish
Max RPM: 1700
Airflow: 121.93 m³/h
Static Pressure: 2.03 mm H2O
Noise: 15 dB (Really? @ 1700rpm?)

Assuming these figures to be right, what would you go for?
The Gentle Typoon doesn't seem to be up to much, but I've seen them recommended before.
The Noctua, while better than the Gentle Typhoon doesn't seem that good either.

Which leaves the Enermax and the Akasa. Noise levels are similar. So the Apache has about 80% of the Airflow of the Apollish, but the Apollish has about 77% of the Static Pressure of the Apache.

So which would be best?

What about in a pull config, which is apparently better for low RPM fans (is 1700rpm low?), does static pressure matter as much then?

I've currently got Apache Blacks, but wondering if I should change some/all for Apollish or something else?

Thanks for your time and advice/opinions/feedback.
 
Manufacturers lie, of the four fans mentioned the best for radiators are the GTs and Apaches
 
I use the akasa which I bought solely on noise levels, it runs very slow on PWM and does not start up until I really stress the CPU (max 1100rpm), it is currently not running while I browse. It is fitted to a thermalright ultra 120 extreme in a push configuration. I am thinking of trying the pull config. as due to the close finning there is some backwash from the fan.
I would think that case airflow is important, for the CPU, a bit of pressure is good, due to resistance from the restricted flows.

andy
 
Biffa said:
Manufacturers lie, of the four fans mentioned the best for radiators are the GTs and Apaches
Click to expand...

Agree with this.

Surely though the fan your getting depends on the radiator cause you are not going to need such high static pressure for a 9 FPI rad as a 30 FPI rad. I would have thought that at low FPI that the volume of air is more important.
 
Greboth is right. For high fin density radiators and heatsinks static pressure is the most important. For low density, airflow is the key.

You match your fans to your rad/heatsink. Hence there really is no such thing as "best" fan or best radiator.

That's why for case fans static pressure is irrelevant and the best cfm for the least noise is always the best choice of fan.

All you can claim in proper reviews is that fan x is best for low density or fan y for high density fins. Same with the radiators. Below 1400rpm an XSPC RX rad beats the Thermochill. At high fans speeds the Thermochill is king again.

And as for your example as to which is best with a radiator on push, a high static pressure or high airflow this is what would happen in real life.

Say you have two fans, one which is 100cfm but low static pressure and another which is 70cfm but very high static pressure.

The airflow is measured with no resistance. In real life on a heatsink/rad, there will be lots.

So with a high fin density radiator you might find the following:

The 100cfm low air pressure fan may only start at 10 cfm and reach a max of 30 cfm on full speed. The 70cfm high static fan may start at 20 cfm and reach 50cfm on full speed.

I hope my basic explination makes sense. If you look at this great review of fans through a rad you'll see what I mean.

http://www.madshrimps.be/articles/article/936/

Of course with a different rad/heatsink you would get slightly different results but it's better than looking at manufacturers info or reviews where they don't put the fan "under load" through a rad/heatsink.

Notice the GT through a rad maxes out at only 34cfm. However, other fans with much worse static pressure only max out at 10 cfm :eek:
 
its definatly subjective.

for instance, radiators with low fpi like thermochill PA, XSPC RX and TFC need certain fan properties to function well

stealth GT rads with high fpi need a hard working fan to move the air through the denser fin population.

in some instances, heatsinks require a different set of fans depending on the design of the sink.

for instance, megahalems work well with slow fans in push pull or with a single fast fan
but little gains are made from having a large cfm fan such as a kaze ultra or a 38mm yate.

it really does depend on the fans position, and remember:

fans that are well suited as case fans arent usually the best choice for your cooling unit [radiator/heatsink]

seeing as it is so subjective it really depends on what you are cooling.

just my 2p anyway :)
 
I have read the above logic and it makes sense that fans are dependent on the Rad type but have a quick question on the following fan

Akasa - Viper
Max RPM: 1900
Airflow: 141.75 m3/h
Static Pressure: 2.98 mm H2O
Noise: 28.9 dB

any good for Rads?
 
allday247 said:
I have read the above logic and it makes sense that fans are dependent on the Rad type but have a quick question on the following fan

Akasa - Viper
Max RPM: 1900
Airflow: 141.75 m3/h
Static Pressure: 2.98 mm H2O
Noise: 28.9 dB

any good for Rads?
Click to expand...

If the manufacturer's figures are correct they would be very good on high density fin radiators requiring high airflow and pressure.

But that's a big "if". The reason I say this is that my San Ace 38mm fans which are one of the best has a lower static pressure.
 
Last edited:
rjkoneill said:
in some instances, heatsinks require a different set of fans depending on the design of the sink.

for instance, megahalems work well with slow fans in push pull or with a single fast fan
Click to expand...
rjk, could this explain why my viper fans sound a lot louder at full speed on my super mega compared to my previous TRUE black, iirc the fin spacing on the ultra was a bit tighter than the mega?
 
sound is a very subjective thing. It can be made at different frequencies dependin on the blade shape.
 
Yep, same fans Greebo, used on two different coolers, the fin spacing on the prolimatech is a bit wider than the ultra, very little difference in temps though between the two coolers.
 
rjkoneill said:
if you have vipers in push pull consider taking one off and trying with a single fan?
Click to expand...
Something i will try rjk, temps in prime 95 dont go over 71c with 2 vipers, (1.2750 vcore in bios, 1.2800 load, 1.264 idle), i was also considering a single/dual 140's as im running a super mega, very hard though to find 140mm pwm fans, though i do have two spare channels on my zalman fan controller.
 
Gentle Typhoon AP-15 1850RPM is great for static pressure vs. Airflow vs DBA. The AP-15 is still the best fan for radiators if you are concerned with DBA, if not then get the Deltas which are kings of static pressure + CFM.
 
Aye, and very noisy, i had sharkoon silent eagle 2000 rpms, arctic f12's, sharkoon silent eagle se's, time i got them they were very rare in the uk, used on my old TRUE black, on a q6600, q9550 and my current i7, currently running akasa vipers on a promlimatech super mega. Next step will be watercooling when i get shot of my current mobo.
 
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