Positive Airflow Quiery

[andrewhutt]

Hello, I need a little hand with my airflow. Below is a diagram of my current set up. I was going to reverse the back 120mm fan and the top 200mm fan and would like to know if that is the correct decision (cannot stay as it is as there is a conflict between the back 120mm fan and the CPU 120mm fan).

[IMG][/IMG]

[peterb]

That probably would be sensible as you would get better airflow over the CPU heatsink.

You could reverse the rear fan and the front bottom fan, but that might reduce the efficiency of the GPU cooling, other than that, there aren't many other options.

If you have some temperature monitoring, do a temperature check before and after and see what difference it makes. Experimentation is always fun!

[AETAaAS]

What CPU heatsink do you have? If your heatsink is amenable to it, my personal tastes would suggest either moving the CPU heatsink's fan bracket to the front (if that is how the fan is mounted) so that it pushes air to the back or simply reversing the fan so that it is in pull.

[andrewhutt]

The heatsink is the Akasa Nero 3. I could put the fan on the other side however the RAM is on the other side and did not want to draw hot air / blast hot air onto it.

CPU Cooler: http://www.overclockers.co.uk/showpr...odid=HS-100-AK

[AETAaAS]

The heatsink is the Akasa Nero 3. I could put the fan on the other side however the RAM is on the other side and did not want to draw hot air / blast hot air onto it.

Uhm, what? That is what your current setup is doing, if your RAM is in the typical position (to the right of the heatsink in your diagram). I think my propositions are a little kinder to your RAM and in any case, you already have the 200mm fan blowing over them which is pleanty of cooling for RAM.

My first proposition;
Turning the fan around so that it sucks air through the heatsink, a 'pull' setup which would avoid what your current setup is doing which is blowing heated air over your RAM.


Alternatively, front mount 'push'. Sucks air from your RAM thus helping cool it with the additional air flow.

[Pob255]

What AETAaAS posted

I would add a 3rd option and that is, leave the cpu as is, flip the rear 120mm fan so it's drawing air in, flip over the top 200mm so it's drawing air out of the case.

Any reason for using positive pressure? and does that case have a dust filter in the top?

A 4th option is to use AETAaAS's 2nd layout diagram but flip the top fan over, this would be a slightly negative pressure but that's not a problem and in current pc case layouts tends to give you slightly better cooling than positive pressure.
That's basically the layout I'm using, Internally the aerocool mechatron is very similar to the HAF 912 I yhave.
I've got my front 200mm as an intake, a 140mm fan on the side panel also intake, with a 120mm in the back exhaust and top 200mm fan exhaust.

[Domestic_Ginger]

As the above's; flip over the cpu fan so its pointing out to the back.

The top 200mm fan is interesting. If I was looking at optimal cooling; I would run four tests monitoring CPU and GPU temps (maybe mobo if there is a sensor). 5 minutes of prime and heaven should do it if the temps have stabilised.

1) fan in
2) fan out
3) fan off.
4)fan on side panel.

I've become a more susceptible to noise and tend to turn things down rather than run cooler.

[andrewhutt]

Thanks for the advice everyone. A slight update or spanner in the works.

After reading through some articles, it appears that a negative pressure in the case is desirable (in terms of less dust etc.) So more exhaust fans than inlets. So based on this my current build I have went for:

Rotated the top fan so that it is an exhaust and moved the cpu cooler fan to the otherside and for it to 'pull' air onto the heatsink.

Also, I think I will attached two 140mm side fans and set them to inlet. Although I am undecided about these as this will mean I have more inlet fans than exhaust.

[peterb]

I'm not convinced about the dust/positive pressure/negative pressure thing. If you don't have dust filters on the fan inlets, you are going to draw dust in. Full stop. It doesn't matter if the airflow in in slightly higher when the fans start, or slightly lower, once the fans are running, there will be an equilibrium - airflow in=airflow out If that wasn't the situation, the case would eventually implode or explode.

What is important is a smooth airflow with few dead spots, and fans working in harmony. Th arrangement in the top diagram of AEtAaAS' post seems pretty good (I didn't realise the CPU fan could be turned round in my earlier post)

[Pob255]

Yes peterb has it there, dust is more about filtering.
The advantage with positive pressure (more intake than exhaust) is that the fans are the only source of air intake, and air should be blown out through any vents, exhaust fans or gaps, this means you only need to put filters on the intake fans/vents.
Negative pressure (more exhaust than intake) means you get dust sucked in from vents and gaps as well as from the fans so it becomes harder to filter out all the dust.
In older cases you had limited vents, the psu took air from inside the case becoming part of the exhaust system and limited space for exhaust fans to be put, so it all benefited more from positive pressure.
However most cases now have far better ventilation, bottom mounted psu getting air from outside the case and lots of space directly around the main sources of hot air (cpu and motherboard VRMs) generally mean you get better cooling form a negative pressure setup.

2nd however, negative or positive is not really that big a deal in most cases, total air flow through the case is the key factor.
A balanced air flow is fine and what many people aim for, but it is more about move the air through the case and not letting it get trapped, positive still works but works best in a case built around positive pressure, eg the silverstone TJ08
The main thing you want to avoid is having two fans trying to pull or push the same air in two different directions, eg in your original diagram you've got the cpu cooler fan and rear case fan trying to pull air away from each other.
Top fans will cause some issue as they are trying to pull or push air at 90 degrees from the main flow but that's not too bad as it's 90 degrees and generally not too close to other fans or only a small part of the fan air flow will get interfered with.