[SOLVED] Higher CPU fan speed = more heat ?

[Kenrou]

Noticed this a couple months ago so i can't say for sure if it always happened, but if i increase my Noctua fans above ~70% i get higher temps in benchmarks/Handbrake, ex: fan curve silent peaks at ~80c and normal/turbo/full peaks ~85c. It isn't a bad mount (i think) as i reset it 2x in the last 3 months and it stayed consistent, could it be that the exhaust fans can't keep up with the D15 when they ramp up even though they push the same amount of air ~70 cfm, or am i creating a problem by keeping the 3x intake and 3x exhaust always at full speed (they are near dead silent) ?

http://www.fractal-design.com/home/product/casefans/dynamic-series/dynamic-gp-14

http://noctua.at/en/products/fan/nf-a15-pwm

 

[trents]

If the case fans are not keeping up you could possibly be getting some kind of back flow eddy that is bringing warmed exhaust air from the backside of the cooler back around to the intake side of the cooler. There also could be some heating due compression of the air against the cooler stack faces. But that would be only be very minor and maybe not even show up without fine temp measuring instruments. How much temp difference are we talking about?

I would try taking the case sides off and see what effect that would have. It might tell you something about case air flow.

 

[Kenrou]

Can do tomorrow i think, its ~5c at peak temps. I honestly think it's awesome having a quieter computer and lower temps but...

 

[trents]

5c delta is quite a bit. I'm thinking it's a case air flow issue.

 

[Kenrou]

This is my current setup, how do i improve on it ?

 

[trents]

Do you think as it is you have positive or negative pressure inside the case? If you have positive pressure then you are more likely to a back flow eddy I would think. So maybe a faster fan on the rear panel. But if "quiet" is more important to you, this is contra indicated.

 

[EarthDog]

The psu in isn't relevant as it goes right back out and doesn't affect anything (assuming fan side down like the drawing infers).

That said, you may just have a Hotspot? Try more exhaust than intake and see what happens.

 

[NiHaoMike]

It could be possible that at higher fan speeds, refrigerant is pooling in the bottom half of the heatsink, reducing the effective heat exchange area. For testing, what happens if you turn the case so that the heatsink is vertical with the CPU at the bottom and the heatpipes pointing up?

 

[Kenrou]

As it is now I should have the same amount of air going in then out BUT the intakes have dust filters so they have to work harder, don't know if it means anything. If i lower the exhaust speed, it becomes hotter under load. As it is now even at 4.7ghz 1.38v it is literally near dead quiet (the air displacement covers up the very little fan noise and if i put on any kind of headphones i stop hearing the setup altogether unless the GPU fans kick in) so guess I can make some noise for a change

So i have 3 options (at least) : could rummage through my big bag o' fans and switch the exhaust for 2k rpm OR add another exhaust on the top (closed at the moment) OR take away one of the intake (maybe the bottom) ?

@E_D : forgot to draw another arrow pointing out the back for the PSU

@NiHaoMike : I don't have the space near my desk to keep it "sunny side up" 24/7 if that is the case

 

[EarthDog]

So, are you saying they are running the same speed but you intakes have filters on them? It absolutely makes a difference... but that should lead to slightly more exhaust than intake too..

Another arrow isn't the point. It has nothing to do with airflow unless it's fan up which takes in case air and puts it out the back. Your drawing has it taking air in the bottom, then assuming through the psu and out. Not relevant is my point.

What do you mean 'closed at tbe monent'? You talking a third fan up top... at the front?

As I said, get more exhaust than intake and see if that helps.

 

[Kenrou]

So, are you saying they are running the same speed but you intakes have filters on them? It absolutely makes a difference... but that should lead to slightly more exhaust than intake too..

So at the moment technically i have negative pressure right ? since i have the same amount of fans at the same speed but the exhaust is running more efficiently then the intake. But it's not enough ?

Another arrow isn't the point. It has nothing to do with airflow unless it's fan up which takes in case air and puts it out the back. Your drawing has it taking air in the bottom, then assuming through the psu and out. Not relevant is my point.

Gotcha

What do you mean 'closed at tbe monent'? You talking a third fan up top... at the front? As I said, get more exhaust than intake and see if that helps.

I have 3 slots for fans on the top but only using the back two and the 3rd that would usually sit on top of the optical bays has no fan and is closed (has the sound dampening cover on it).


I don't have any fans at home better then the ones installed so will probably have to shop. Would a NF-A14 industrialPPC-2000 at the back take care of it since it has much higher cfm and speed then the Noctua ?

 

[trents]

So at the moment technically i have negative pressure right ? since i have the same amount of fans at the same speed but the exhaust is running more efficiently then the intake. But it's not enough ?



Gotcha



I have 3 slots for fans on the top but only using the back two and the 3rd that would usually sit on top of the optical bays has no fan and is closed (has the sound dampening cover on it).


I don't have any fans at home better then the ones installed so will probably have to shop. Would a NF-A14 industrialPPC-2000 at the back take care of it since it has much higher cfm and speed then the Noctua ?

I would think so. I would even be tempted to unplug all but the fan in the rear and the most rear top fan and see what effect that has. The top fan that lines up wit the front side of the cooler may be pulling warmed air from around the back of it and negating the exhausting effect of the rear and top rear ones.

 

[NiHaoMike]

@NiHaoMike : I don't have the space near my desk to keep it "sunny side up" 24/7 if that is the case

That's just a quick way to test it. If it does make a substantial difference, you can remount the heatsink so that the heatpipes are horizontal.

 

[orion456]

Duct the cpu output fan to the back of the case so no air can flow around and back in the cpu intake.

At high speed you are pushing so much air it probably cant all escape thru the back case hole and some hot air is recirculating to heat up the heat sink from the cpu intake.

Most fans don't blow straight out but instead blow to the sides of the fan so the escaping air makes a funnel shape with most of the air on the outside edge of that funnel. That allows a fair bit of air to spread into the case if the fan is not ducted to the outside.

 

[Kenrou]

Sorry for taking so long to update, ended up buying 2x NF-A14pwm, they will arrive in the mail today and will assemble them a bit later on. If these work out how they are supposed to i will switch the other 3 fans in my case as well. Tried NiHaoMike's suggestion of tipping the case but didn't seem to make any difference

http://noctua.at/en/nf-a14-pwm/specification

New layout :

 

[Kenrou]

~8c difference at max fan speed and no more hotspots in the area, problem solved. Thanks everyone for your help

 

[trents]

So it seems it was a back flow issue caused by exhaust fans not keeping up.

 

[Kenrou]

Yep, after a little re-wiring (dumbass me forgot that the speed controller from the case only takes 3pin) everything seems to be running like clockwork. Only problem now seems to be a very cold airflow in this area when they ramp up which is currently in the process of freezing my tenders