cooling: optimal airflow ?

[VJ]

Hello,

After some advice on a dual AMD mainboard (in another thread), I have some questions wrt. cooling. My case is a LianLi PC-70, which has 2 80mm intake fans at the bottom front (2 10K drives are mounted in the drive bay behind this).
At the back, it has 2 80mm fanholes at the top of the case (above the PSU), 2 80 mm fans located above the PCI-slots (approx. at the height at which the CPU can be found) and 3 40mm fanholes next to the PCI slots.

Now, my question is: suppose I put fans in all those holes, this would result in 2 80mm intake fans, but 4 80mm + 3 40mm + the PSU fan that blow air out of the case. Is this a good balance for airflow ? I thought you'd need approx. the same airflowcapacity for intake and outtake.

What would be the best configuration of the fans in this case to cool it as efficiently as possible ?

Thanks !


Jörg

[Fat Tone]

Fan size isn't the only factor. Speed & design will also affect throughput. You need to look at the CFM for each fan and add them up. It doesn't matter if they are a bit out of balance.

T.

[RichL]

Re: cooling: optimal airflow ?

Originally posted by VJ
I thought you'd need approx. the same airflow capacity for intake and outtake.

That makes sense, but when I think about it my Globalwin case has an 80mm intake as standard, sucking air through a filter and one of those awful pre-punched grilles, both of which impede airflow hugely, and on the output side it has an 80mm fan with no filter and a decent pre-punched grille, plus the fan in the PSU.

Thats as standard and the Globalwin is considered a good case for cooling.

My own case has benefited from some butchery around the intake fan to remove the grille and filter, an Enermax PSU with twin fans, a system cooler mounted below the G400max and, my most effective mod, a fan duct made from a speaker bass port mounted directly over the CPU heatsink, so it sucks air almost completely from outside the case. Both my HDDs are fitted with low profile coolers, and the topmost 5.25inch bay is a removeable HDD cage, which comes with its own low output 40mm fan blowing a little air into the PSU.

Right now, with an ambient room temp of 27c, my case is 31c and the CPU is 38c, thats with nearly a full load of PCI cards (see sig) plus a Voodoo 5500 pci in the lowest slot in the case.

[xortam]

I would think that you would want more output pressure than input as the slight vacuum would make for more efficient cooling. The grills are supposed to be designed to reduce electronic noise emissions while minimizing their impact on flow rates. I checked the Intel site regarding case design before I bought my system three plus years ago: It was a pretty interesting read.

[Technoid]

Most case manufactors seems to just punch holes in the sheet metal to make the grills

[xortam]

Its the openings' size, shape, and placement that's important. Here are some pics of the ventilation on my LiteOn TI800 mid-tower case. Its sold as an OEM Xeon case w/ 120 mm intake/exhaust fans.

[birdy]

I believe that a slight vacuum (we are talking incredibly slight here using pc fans) actually harms cooling. The reason is that the HSF requires a medium to move the heat onto, in this case the air, If there is less air then there is less medium to move the heat to therefore it stays more in the heatsink. Although if you blow air in then you get more medium for conduction but it still has to exit the case which isnt easy when you have all your fans blowing in.
Good cooling relies on through flow of air so the ideal combination is to have fans blowing in lower down the case and fans sucking out nearer the top.
My self i have a 92mm blowhole directly above the cpu with an antec fan (blowing in) fitted and another 92mm blowhole at the top of the case sucking air out. That way the coolest air goes over the CPU, past the hard drives and then out of the top.
I like the idea of a bass tube directing the air straight at the cpu, i might give that a go.

[RichL]

Originally posted by birdy
I like the idea of a bass tube directing the air straight at the cpu, i might give that a go.

Thanks, I think I'm one of the first to do it. Most people install a fan above the CPU cooler, but in experiments involving a 10" desk fan and the side of the case open, I found blowing air onto my cooler decreased its speed by a couple of hundred RPMs and didnt have much effect on the temp of the CPU.
The duct actually works well, recently my system temp hit 34c and CPU was 41c at idle. Removing the side of the case dropped system to 32c but CPU went up to 43c.

The pic shows the duct in all its glory. Yes, it is off center. It was a case of measure once, twice, three times for luck, then cut eighteen times as the cutter went blunt, came loose and fell apart several times during the operation.

[birdy]

very nice mate

I don't have to worry about the dpu fan slowing down. It doesnt have one

Arent zalmans great

[VJ]

Tony:
Yes, well the 4 currently present fans were mounted as standard and are all of the same brand.

Here are some pictures of the case:

http://www.lianli.com/11302001jcL_pc_case/jclpccase/jclpccase/pc70.html

Notice how the lowest drivebay puts the drives behind the intake fans; the grill/filter are quite good (not restricting the airflow that much).

Anyway, how would you mount the fans in this ? Just start with the "standard" 4 fans, and see if it remains cool ? (if not, put in the 3x40mm fans, blowing out ?)


Jörg

[Fat Tone]

I'll ask Paddy to respond with his experience of this case: His is basically the same but with a large window.

T.

[Paddy]

I have the LianLi PC75. As Tony states, it is the same case but with a large Perspex window on the left hand side. When I purchased the case I was fairly disappointed with the stock cooling.

System specs:

Asus A7M266-D, one XP1800+, 80GB ‘cuda IV, 4 8GB IDM SCSI disks, 106s DVD, PX1210S, two Adaptec 2100S SCSI RAID cards, AIW8500DV, Live! 5.1, Asus 2.0 USB hub, Intel pro100 nic. And probably some more…

With the stock fans and a Zalman flower on full I get mobo 35’c, CPU 43’C idle AND both sides off!

There seems to be a pocket of hot air at the bottom/back of the case and at the very top. I quite often see internal temps exceeding 40’c! Although some of this is due to the mass of SCSI cables.

Looking at the structure of the case, I would recommend having an exhaust fan at the top of the case. Unfortunately, as the both side panels can be removed, the top is part of the structural integrity… and it’s an expensive case to mess us!

My old globalwin 802 had the same hardware jam packed into a much smaller case. Thinking about it, it also had the same number of 80mm fans. I never had a problem with cooling on that baby.

My CPU temps never exceed 46’C but it’s the ambient temp that bothers me.
I think that because the case is quite large, it is difficult to shift the air about. The stock fans at the font do a great job at cooling my hot drives, but they just move the hot air back into the depths of the case. The exhaust fans are placed halfway up the case and so there is always warm air above them.

I am not happy with the cooling. I just don’t know how I can improve it without hacking the top of it off. I think I am going to water cool a few bits and have a rad in the roof. But I need more intake fans too. It is going to be difficult to site them without making it look like a mess. I am currently thinking of placing some big, low voltage fans on the floor of the case….

Not sure if any of that is going to help! Please forgive me, I have just come back from a weekend away and I am very tired!

If there is anything specific I can help with, just ask!
Paddy

[xortam]

You realize that by removing the sides of the case that you're possibly creating a electrical noise problem with your nearby electrical devices?! You're also defeating the air flow design of your case by removing its sides. Removing the sides may assist cooling in some instances but those are the exceptions.

Paddy, what's the affect of your ambient temperatures between having the sides on versus off? You should concentrate on finding any obstructions of the air flow inside your case.

You should check the Intel site for that paper on case design. I believe they covered air flow design principles.

[Fat Tone]

http://forums.murc.ws/showthread.php?s=&threadid=34693

[Paddy]

Cheers Tony!

Xortam:
I have minimised obstruction where possible, except for a few cables. The problem i have is there is no airflow between the PCI cards. Those Adaptec SCSI cards generate a lot of heat.

Taking the side off of the case does improve the cooling by a few degrees.

Nothing creates noise like a perspex window I have not had any problems with the sides off so far mate.

Thanks.