Case air cooling with only top fans.

[MrCravon]

So, my new case (H300mm,W130mm,D450mm) has holes for airflow only at the top and bottom. The motherboard is oriented so that my IO is in the bottom of the case and the GPU works sort of like a divider making "two rooms" in the case as shown in the picture. I have 4x92mm fans in the top. Now my question is:

 

Should I:

A. Pull air up through the case using dust filters in the bottom and effectively creating negative pressure in the case. In this configuration the fans would work "with" the heat as hot air rises upward.

B.Push air down through the case. Positive pressure in the case but working "against" the rising hot air.

 

Also in alternative A. There is a possibility that the PSU will suck back in it's own exhaust air. I tried to illustrate this in the drawing. EDIT: (A and B is labled wrongly in the drawing, it should be opposite.)

 

Any thoughts on best practice?

[mrgooglegeek]

Negative pressure is not a bad thing. I would not suggest fighting the hot air rising. If you have some really small fans laying around, you could stick them in the bottom. That might help a little with intake but i doubt it would matter all that much.

[LogicalDrm]

Which case would this be? No offense, but I like real pics better than diagrams. More so when we are talking about something else than basic ATX tower.

[MrCravon]

This is the case: http://www.genesysgroup.com.tw/c330.htm

 

However i have modified it. Originally the case has space for 4x60mm fans in the front panel. As well as two 60mm fans on the right side panel and one in the back. It also has an intake port on the top for the PSU and an passive grill under the PSU and one the left side panel. However, I am using this case in a 19" rack bag as shown below.

This makes the side and top and bottom panels flush with the other items in the bag or with the walls. Effectively making the front and the back panel my only options for cooling. Now the rack bag has feet as shown in the picture allowing me to have it standing which orients the computer so that the front panel becomes my "top" panel as shown in my previous post. The result was inadequate air flow especially in the area of my PSU and GPU as the GPU effectively blocked airflow to that side of the case. So I made some modifications to the front panel (or "top" panel in my case) so it now looks more like this:

 

 

 

I also removed all the HDD holders and the likes to make space for the GPU, and substituted my own. I haven't really finished the new font ("top") panel yet but thought i would ask about airflow to make informed decisions.

 

Thanks for the replies so far!

[MrCravon]

Oh, and by the way, it is a basic fullsize ATX board and PSU inside the case. 

[LogicalDrm]

I still have really hard time to get orientation of everything. But I think your biggest issue here is that there isn't that much space under case. You can forget "hot air rises" -thing when talking about air movement inside case. Passive air movement is much slower than airflow created by fans. Which means that fans control airflow inside case, passive outside it.

 

Keeping that in mind, and since you don't seem to have much clearance under case, I'd say go for option A. Even if you could make case stand bit higher (I think even 1cm more room would help), better option would be laying case on its side when you are using it.

[MrCravon]

11 hours ago, LoGiCalDrm said:

 

I still have really hard time to get orientation of everything.

 

 

Yes, in my first post i labeled the case panels by the orientation i currently have it placed in. Which might have confused things a bit. I apologize. Maybe the picture below helps. It is labeled with the orientation the case has in the rack bag when the rack bag stands on its feet like in the picture in the above post.

[LogicalDrm]

14 hours ago, MrCravon said:

 

Yes, in my first post i labeled the case panels by the orientation i currently have it placed in. Which might have confused things a bit. I apologize. Maybe the picture below helps. It is labeled with the orientation the case has in the rack bag when the rack bag stands on its feet like in the picture in the above post.

 

That helped. But I still stand behind my previous thought. Clearance between case floor and surface under it isn't wide enough for good cooling.

[Dschijn]

I would try and use all fans on the top as intake, if the GPU will exhaust hot air at it's I/O on the back. The air will be forced out at the back/bottom.

With the fans forcing all the air out (exhaust), the PC would try and suck the air into the case at every possible "slot". E.g. the passive case openings and the hot air of the GPU.

If the GPU does not exhaust hot air, you could try and use all fans on the top as exhaust.

[MrCravon]

On 4/28/2016 at 0:03 AM, LoGiCalDrm said:

That helped. But I still stand behind my previous thought. Clearance between case floor and surface under it isn't wide enough for good cooling.

Because the whole PC is inside a carry bag I have the possibility to just hang it under my desk using hooks attached to the carry strap fastening points. I have been thinking about that and will try how much of a difference it makes. Thanks for the input.

 

On 4/28/2016 at 0:17 AM, Dschijn said:

If the GPU does not exhaust hot air, you could try and use all fans on the top as exhaust.

My GPU is a Gainward GTX970 "Phantom" and it does not have one of those blower style fans that exhaust out the back only. As of now I have mounted the top fans as exhaust and will see how that works for now.

 

I have encountered a problem though that you fine people might be able to help me with. The fans always spins at top speed. The four fans i have installed in the top are Noctua NF-A9 PWM fans. They are each connected to a low noise adapter which in turn is connected to a splitter like this:

Which in turn are connected to a PWM header on the motherboard (Asus Sabertooth P67 CHA_FAN1) and to the PSU.

 

I have tried the BOIS settings in the motherboard set to Q-fan silent and manual. I tried Speedfan with Q-fan both disabled and enabled. Nothing makes a difference.

 

Any suggestions?

 

[MrCravon]

So I brought out the old oscilloscope and did some measurements. Seems the PWM pin is always at +5v. 

[Dschijn]

With the fans running at full speed I would say that they don't get the PWM signal or the PWM signal is always at 100%.

Most older mainboards only have one PWM plug, the CPU_FAN header. Please check the manual of your mainboard and see if the CHA_FAN1 header is PWM.... I doubt it can PWM!

[MrCravon]

14 minutes ago, Dschijn said:

With the fans running at full speed I would say that they don't get the PWM signal or the PWM signal is always at 100%.

I belive you are correct. I measured it with my oscilloscope and the pin is always at 5V.

 

15 minutes ago, Dschijn said:

Most older mainboards only have one PWM plug, the CPU_FAN header. Please check the manual of your mainboard and see if the CHA_FAN1 header is PWM.... I doubt it can PWM!

Here is an excerpt from the manual. I belive the CHA_FAN1 header should be PWM controlled.

 

[Dschijn]

Yeah he should be, mhhhhhhh. Can you recheck the BIOS again? Maybe you forced the header to be voltage controlled? Any other fan control tool interfering?