Seeking thoughts on cooling with counter rotating vs 'single barrel' fans.

[frogtech]

I'm looking at doing another cluster build...and want to keep the RU as low as possible and depth as short as possible.

I've narrowed my chassis choice down to a few options, either I'm going to do a ATX dual-proc build or ATX single-proc build for each node depending on if I can successfully class 2208 to 2308 IT mode (there's a guide on the web for it).

Question is, between the 2 chassis I'm looking at,

• 1 uses 2 counter-rotating, 40mmx56mm pwm fans that pass air mostly right over the CPU/socket area
• 1 uses 4 40x28mm single barrel pwm fans that pass air mostly over the CPU/DIMMs

At most I'll be cooling:

• 1 or 2 processors, possibly 70w,90w,115w,130w chips just depending on whatever happens to be a good value at the time, with 1U passive heatsinks
• a maximum of 8 DIMMs, either 8 DIMMs for 1 Proc or 4 DIMMs x 2 for 2 procs (limited by ATX form factor of X9 series boards)
• one 10GbE AIC

What I wanna know is, if I get the chassis with the 2 40x56 fans, would the 2 counter-rotating fans be enough to cool such a setup?

I know there's a few people on the forums who've asked previously about replacing 40mm fans with Noctua equivalents to reduce noise but I find this isn't advised since the reason they don't make as much noise is because they don't move as much air(e.g. spin at the same RPMs). This makes sense to me. I probably wouldn't replace the counter-rotating fans to be honest, since only 2 per node shouldn't make as much noise as having 3-4 nodes with 4-5 fans per chassis...

And lastly, in a chassis that already uses 40x28 fans ("single width"), could those be replaced with Noctua fans and still have adequate cooling performance?

 

[BLinux]

at the TDPs you're talking about, I would definitely not replace them with low CFM quiet fans. i've never seen a 1U heatsink with slow fans cool 130W TDP successfully...

it's hard to answer your question without more details like the ratings (CFM, static mmHg) of the fans and ambient temps. but even then, it is probably easier to see what the specifications are from the chassis designer/manual on max TDP rating for what the chassis was designed to cool.

i have some C2758 based 1U systems that run very quietly, but that's TDP=20W only so you can get away with it, but even then it gets warm.

 

[frogtech]

it's hard to answer your question without more details like the ratings (CFM, static mmHg) of the fans and ambient temps.

The counter-rotating fans are the FAN-0087L4 which are rated for 23 CFM (12000 RPM [Inlet] / 8900 RPM [Outlet]) and the single-barrel fans are the FAN-0065L4 which also move roughly 23 CFM (13000 RPM) of air.

The dBA is roughly the same, 56 ish for the 40x56 and 52 for the 40x28.

 

[BLinux]

The counter-rotating fans are the FAN-0087L4 which are rated for 23 CFM (12000 RPM [Inlet] / 8900 RPM [Outlet]) and the single-barrel fans are the FAN-0065L4 which also move roughly 23 CFM (13000 RPM) of air.

The dBA is roughly the same, 56 ish for the 40x56 and 52 for the 40x28.

i haven't done the calculations, but unless the ambient/intake air temp is really low, i doubt 23CFM will be enough to cool a 130W TDP on a 1U heatsink. the counter-rotating fans probably have better pressure, so it might do well if you funnel the air flow from several of those into a narrow path across the heat sources; this might provide improved cooling, but still i don't think enough to cool 130W.