80mm or 120mm fans for static pressure?

[thestraycat]

Hi guys, replacing the midplane fans on my 24 bay "x-case 424S" which is a 24bay norco-esque copy.... Noticed that 80mm fans are generally better at static pressure than the 120mm fans so was thinking of putting in 80mm fans as case runs hot.

 

However, the very top and very bottom disk bays wont be directly in front of the 80mm fan as it's smaller. noticed that newer 24 bay enclosures come with 80mm as standard do you think it'll be more performant? From what i can see because 24 drives takes up ALL the space at the front of any 24 bay 4u server in theory it dosnt seem to be any less effiicient than buying a new case and running the stock 80mm fans.

 

Opinions?

Edited November 26, 2021 by thestraycat
adding

[uldise]

it depends. look at Noctua as example. 120mm fans have more static pressure than 80mm.. comparison between various types of fans: https://noctua.at/en/nf-a12x25-performance-comparison-to-nf-f12-and-nf-s12a 

[aburgesser]

120mm fans will give better performance metrics in every category save space. It's roughly twice the fan area using 120 mm over 80 mm. Always seek to fit the largest fans your hardpoints allow.

[thestraycat]

@uldise - These are I hear what your saying with the noctuas but they seem to be more in pc/gaming bracket in terms of performance i was comparing nidec/delta fans in the 80/120mm sizes that consume around 10 times as much power but have much larger static pressure figures. I'm wondering whether aerodynamically when you get into server grade fans whether 80mm starts becoming a better compromise of back pressure vs noise vs performance. 

 

@aburgesser - Can you give me an example of server grade fans where the 120mm fan out performs the 80mm in the same price range or product line?

[wayner]

Isn't it obvious that a 120mm fan will outperform an 80mm fan given 2.25X larger surface area and fan blade?

 

Are you sure about the 10X power figure?  Fans shouldn't take much power at all and I can't imagine there would be a huge difference between power consumption.  Again a 120mm would be better as you could run the fan at a lower speed which should use less power, and move just as much air.

[Squid]

Not necessarily.  CFM and static pressure do not go hand in hand, and a high CFM 120mm may have quite a poor static pressure rating which makes it completely unsuitable for certain cases where a high static pressure 80mm will cool far better even though it has a lower CFM

 

Power rating on some fans do get to be extreme.  You can easily purchase Delta 60-80MM fans for servers with a rating of 2A

 

The noise level of those fans however is rather high.

[S80_UK]

Yeah... Higher end server fans are a breed apart, they can certainly scream and take significant power.  They can also damage fingers if one is not too careful.  

Edited December 15, 2021 by S80_UK