Cooling

Re: Positive air flow vs. Negative air flows.

cssfozzie — Fri, 03 Jul 2009 22:15:17 GMT

Great information!

<--HVAC building engineer

1) Heat always stratifies at the top--air is more dense closer to the ground, heat travels from most to least dense. Even having a top outlet... not necessarily a fan, is crucial for getting rid of that stratified heat (eegads, right next to the power source) needless to say a fan is better

2) Make damn sure you have enough room for the air to move where ever you have an opening in your case, and that you're not sucking in hot air from somewhere else in the room (i.e. floor register). keep at least a few inches clear; i try to keep min 6". Restricing the orifice has an exponential effect on the air flow (not linear relationship)

Re: Positive air flow vs. Negative air flows.

HOGHAULER — Sun, 28 Jun 2009 05:15:43 GMT

Another point to ponder your PSU also has a fan pulling air out of the case and trying to keep itself cool so too many fans located around the PSU trying to exhaust hot air out can result in your PSU heating up!

Re: Positive air flow vs. Negative air flows.

FascistNation — Sun, 28 Jun 2009 00:53:13 GMT

This is a wonderful account, and not particularly surprising to me. But nice to confirm old data is still running true.

Special cooling conditions: Weird cases, RAID (front fans) or dual video cards. In all situations temps should be monitored to confirm an overheating problem exists before action is taken as your data clearly shows, too much can actually degrade cooling (and add to power drain).

Negative or positive---either way unless you are sucking air through dust blocking filters in the latter you are drawing dust into your case. Especially the lower to the floor the intake(s) are.

Additional comments on this topic by Scott Mueller. And note the dissenting opinion that starts the discussion off.

One last note: If someone is considering moding their case by adding a fan port or side port, it is very wise to strip your case out (or remove your case door respectively) so you can remove ALL metal filings that will result. Because as anyone who has done it once can tell you those little SOBs can be difficult to remove and can short out your expensive parts if they remain inside your case.

Re: Positive air flow vs. Negative air flows.

prtuc2 — Tue, 23 Jun 2009 23:48:31 GMT

Sorry for the late reply everyone just too busy searching for employment lately.

If you setup as negative air flow system you will have more dust inside the case, but in my opinion is how everything is lay out inside the case. Just like what Hoghaluer said, large video cards and wires can redirect or block air flows inside the case, so not everyone might experiences the same level of cooling effects.

Most of the current cases have side panels fans which will give additional intake air flows into the case as a balanced air flow to the top and rear fans as suppose only 1 fan on the intake. As long as the case air flow is balance well, the overall case temperature should be fairly close to the ambient room temperature unless you running some cpu or gpu intense applications.

As many of us know hot air rises and cold air sinks, so having a top rear exhaust fan can really lower the overall case temperature by removing them outside, however if you got a very warm room then is not going to help much. Another reason for top rear fan is the heatsink orientation you can mount it parallel to the rear fan or to the top fan depends on how you like it or if NB is blocking the installation.

I won't say negative is better than positive just make sure the overall case is balance air flow, having more airs exiting always makes more noise keep that in mind. Depend on the case, but usually one top fan is sufficient to get decent temperature if you don't like the temperature you can always add a second fan on the top. Positive air flow recommend in cooler room and negative air flow in warmer room in my opinions.

Sorry once again for the outdated article, if you got more questions feel free to ask.

Re: Positive air flow vs. Negative air flows.

TheLarrikin — Tue, 23 Jun 2009 19:11:57 GMT

Thanks for that, Pops. :)

I come back on a whim, one day in however many months (I've been working my arse off), and find this - :) It's nostalgia at it's finest. :)

I'll come back on here sometime and catch up with you all. Must be going. *sigh*

Re: Positive air flow vs. Negative air flows.

HOGHAULER — Mon, 22 Jun 2009 23:38:41 GMT

Good post there prtuc, excellent explanations on the hows and whys but the one thing you did not dwell on was the blocking of airflow due to component position and wiring blocking that airflow and causing disruption in same. I wish they had tested that out too.

Re: Positive air flow vs. Negative air flows.

LiteBulb — Mon, 22 Jun 2009 22:21:36 GMT

According to the temperature graphs, the top and rear configuration worked the best to keep things cool. However, wouldn't this setup be bad for dust, since there is way more exhaust than intake?

Having positive air flow rather than negative air flow was highly touted as the better setup. Is this just in terms of dust and not temperature?

I am confused.

So would it be better to have two intake fans and one exhaust at the top or rear? Or maybe two intakes on medium and two exhausts on low?

Re: Positive air flow vs. Negative air flows.

cipher — Thu, 11 Jun 2009 20:09:52 GMT

Thanks for the interesting links. As PapaHomer mentioned, we had some good conversations on this before.

The Silverstone page on this was very well done.

However, the other one is dated and a little on the amateur side of testing. It really didn't explain how they tested it, just the parameters for their test, and on an older system. That article is from 2003!!! PCs, their cooling systems, and type/amount of heat generated has changed quite a bit since then.

Re: Positive air flow vs. Negative air flows.

rogue1266 — Thu, 11 Jun 2009 17:57:53 GMT

Yeah, Thank's for this post. Good Info...

Re: Positive air flow vs. Negative air flows.

nerdrage — Tue, 02 Jun 2009 19:33:19 GMT

These were some very interesting reads, thanks for the posts. Now I can definitely plan my new rig a bit better.

Re: Positive air flow vs. Negative air flows.

prtuc2 — Sat, 16 May 2009 00:25:10 GMT

TL got some great posts, nice find I was looking for the same thread just can't find it so just post this up instead.

Re: Positive air flow vs. Negative air flows.

PapaHomer — Sat, 16 May 2009 00:22:49 GMT

Very clear and easy to understand.

Another good one: TL explains positive and negative case airflow

Thanks

Re: Positive air flow vs. Negative air flows.

mrtraver — Sun, 03 May 2009 20:50:28 GMT

Funny; I just changed an exhaust fan for an intake last night before seeing this sticky, to create positive pressure. Dust was collecting around the seams for the side door, as well as around the optical drives, I/O ports, and even the case latches.

Re: Positive air flow vs. Negative air flows.

Tracer76 — Wed, 29 Apr 2009 21:52:35 GMT

That is very helpful thanks for posting it prtuc2

EDIT: Yes I did sticky it

Positive air flow vs. Negative air flows.

prtuc2 — Wed, 29 Apr 2009 20:47:18 GMT

Every once a while I see people asking which direction my fans should be going and here are some answers. Some of the displays required adobe flash player in order to view.

http://www.silverstonetek.com/tech/wh_positive.php?area
http://icrontic.com/articles/pc_airflow_heat_cooling_guide <<--Source

The parts and mod list

AMK SX1000 PC Case
ABIT KV7 Motherboard
AMD 3200+ XP Processor
2 x 256 MB Corsair XMS DDR 400 Memory
Enermax 465 PSU
ATI 9700
PRO Video Card
Zalman CNPS7000A Heatsink
60 GB Maxtor Hard Drive
Rounded EIDE cables
2 x 80mm. front intake fans
2 x 80mm. rear exhaust fans
2 x 80mm. side intake fans
1 x 80mm. top blowhole
WindowsXP

How the tests were conducted

Each test was conducted with a room temperature of 23.6 +/- 0.4 degrees Celsius. The system idled in its testing configuration for 30 minutes prior to Sisoft Sandra CPU burn-in (CPU Arithmetic Benchmark/CPU Multi-Media Benchmark) run 100% stress for 25 consecutive times. Motherboard Monitor 5.3.4.0 recorded the results at 5 second intervals. “Idle” temperature was determined by the consistent temperature reading for 20 measurements recorded prior to the burn test. “Time to idle” was determined by the amount of time in minutes and seconds from the last peak CPU temperature until the first reading of the “Idle” temperature.

Testing configurations

The basic AMK SX1000 case is a very common and popular PC case for enthusiasts under whatever manufacturer name it happens to be.

We installed matching 80mm. fans and drilled holes where fans weren’t meant to go. First two fans in the front.

Then two fans in the rear.

Then a top blowhole.

And finally two fans in the side.

With all fans in place it looks like quite a lot of cooling power.

We’ve always been preaching the golden words of cooling; “in through the front and out through the rear…or top”. This is the golden rule when it comes to all PC cases for air cooling no matter what components are inside.

But, having too much time on our hands, we questioned ourselves. After all we are the same people who came up with a 1700 CFM case and a ghetto duct made of cardboard. It only seemed appropriate that we journey down this road. We questioned ourselves as to the effectiveness of so many fans with so many conflicting airflow patterns. Could it be that more fans isn’t better? Could it be that the airflow may become quite a mess thus diminishing the overall effectiveness?

So we spent a few days looking at thermometers and watching a PC cook itself. 10 different configurations were tested in our quest to determine how airflow affects heat.

No fans

All fans

Rear only

Top only

Side only

Top and front

Top and side

Top and rear

Rear and side

Rear and front

A word to the wise

A PC case is essentially a box. It can be safely said that there is a consistency to ALL PC case configurations; processors, video cards and drives are generally in the same area. However the specific style of PC case and type of components varies greatly from user to user. These differences will affect your specific results. CPU temperatures may be higher or lower depending on type of heatsink and processor. Another extremely important variable for testing is ambient room temperature. The temperature of a room, warmer or colder, can greatly affect personal results. We’ve intended these tests to demonstrate the combination of fans and their effect on cooling. This may not be the rules set in stone for all but they will surprise you and give you food for thought.

The results

Surprised?

Conclusions

We would be lying if we weren’t. It was our assumption that the tests with ALL the fans in operation would produce the best results but it didn’t. Time to idle represents how effectively the configuration removes heat from the PC case. The shorter the time the better. CPU peak and idle as well as System peak and idle are easy to interpret. We would like to think that System temperature represents an average of how cool every component in a PC is.

The top and rear exhaust produced the best CPU and System results but nearly placed last for time to idle. We tested three times for this result as we didn’t believe the first two.
A single rear exhaust fan produces the best results overall. This flushes the theory of more is better right out the door.
A top only or top and front combination places in the middle of the pack for CPU and System peak cooling BUT does whisk away the heat in a very short amount of time.
Even with no cooling fans besides the heatink…heatsink size and type of fan can deliver good results.

So there you have it. A few theories dashed upon the rock perhaps. At least for this type of PC case and components. What should be taken away from this? Quite simply that more may not necessarily be better but, for us enthusiasts, more may be cool…for looks.

What is positive air pressure?

　　 Computer chassis are typically equipped with many case fans, some are designed for exhaust and others for intake. When intake fans’ combined airflow is greater than exhaust, a positive pressure is created inside the chassis. Conversely, when the airflow is greater for exhaust than it is for intake, a negative pressure is created.

How does positive and negative pressure affect airflow in a chassis?

　　The major difference between positive and negative pressure is the way vents and various gaps are affected.

　　 This photo shows an example of a modern high performance chassis with extra vents not occupied by case fans. These vents can become either exhaust or intake depending on whether the chassis has positive or negative air pressure respectively.

*Dedicated vents aren’t the only places on a chassis that can act as pathways for airflow, gaps on the outside the chassis such as the one shown in this photo can also be affected.

The benefit of having positive air pressure：

Benefit 1： Dust reduction
　　Newer case models now sometimes include fan filters in an attempt to reduce dust build up inside the chassis. If the chassis has positive pressure, only intake fans require fan filters to effectively reduce dust build up.

　　 The diagrams show that chassis with positive air pressure can prevent dust from penetrating into the chassis by use of filters on intake fans and forcing air out of the chassis through unfiltered vents and gaps. On the other hand, a chassis with negative air pressure draws in air from unfiltered vents and gaps that even with fan filters placed on key intake fans, dust can penetrate into the chassis easily.

　　The idea to use positive air pressure in designing dust-proof chassis comes from the concept of a cleanroom. The cleanrooms are used often in Hi-tech, medical, and food processing industries. All cleanrooms, regardless of their levels and sizes, are built to maintain a positive pressure environment to prevent dust from entering the room.

Benefit 2： Maximize graphics card cooler’s efficiency

　　　　　Left： Partially sealed graphics card cooler 　　 Right：Fully sealed graphics card cooler

　　 Currently, all original graphics card coolers (non-custom) are designed to exhaust air toward the rear to prevent heated air from being recycled back into the chassis：

Partially sealed graphics card cooler：

Diagram A：Heated air are blown partially out of the chassis with the rest remaining inside the chassis

Diagram A-1：

In a negative pressure chassis, heated air that is suppose to be blown out will re-enter the chassis through openings nearby and raising the chassis temperature.

Diagram A-2：

In a positive pressure chassis, all heated air from the graphics card will exit the chassis, keeping overall temperature low.

Fully sealed graphics card cooler：

Diagram B：

Fully sealed graphics card does not exhaust heated air into the chassis, but the fan in the cooler is affected by the pressure inside the chassis.

Diagram B-1：

In a negative pressure chassis, the air from outside will try to enter the chassis through all openings, including the graphics card exhaust opening. As a result, the fan in the graphics card cooler need to work harder to push the air out, becoming less efficient and likely to be more noisy.

Diagram B-2：

In a positive pressure chassis, air will try to escape out of the chassis through all openings and exhaust fans. As a result, the fan in the graphics card cooler, which isdesigned to exhaust air out of the chassis, will work more efficiently with increased airflow and less noise.