Balance caseventilation a myth?

[Santa Claus]

Hi, i have many times heard people say its important to balance the ventilation in cases so an equal amount of air is drawn into the case as blown out of the case by fans.
I have asked about this many times but sofar noone have been able to give me a good explanation so feels more and more like a myth.

Does it really matter if its balanced or not as long as the airflow isnt obstructed and air can reach all components of the computer?

Regards

 

[The Jinx]

I've also heard this too and logically it makes sense because you don't want trapped hot air inside the case (ie your air inflow is higher than the air drawn out). But truthfully i don't know and i currently have more air being drawn out than in.

 

[cyclone3d]

You basically need sufficient in and out air flow.

As for the pressure thing, it is probably a little better to have a slight pressure inside the case due to denser air being able to transfer more heat.

 

[luddha]

I think it's better to have a little bit of pressure in the case if you want to keep dust away. I have more intakes then fans blowing out.

 

[Asian PingPong]

Ideally, you do not want equal pressure. Equal pressure means that the air is only flowing through the fans, and is not entering/exiting through the other vents and openings in the case. This airflow through vents and openings helps to cool the hard drives, video cards, chipsets, etc...

That being said, there are now two choices, positive pressure or negative pressure.

The main advantage of positive pressure is that all the airflow through the case enters through fans. If these fans are filtered, and since air isn't being intaked by vents/openings, all airflow into the case will be filtered.

However, positive pressure can lead to hot spots, where a mass of air is not being circulated, and gains heat without having any place to escape. As such, negative air pressure is generally better for cooling.

 

[dystopic]

i wouldn't call it a myth so much as an exaggeration in a negative light, and in a positive light, a guideline. i'd also say it's a more meaningful guideline if you're pursuing a maximum overclock on air cooling.

 

[sprocket]

For the most part I think "positive/negative pressure" and "case airflow" are, if not outright myths, then at least, wishful thinking.

The average case, with average casefans, doesn't move enough air to build up noticeable pressure- not to mention that the average case is so riddled with holes and gaps that "pressure" couldn't be maintained, even if generated.

 

[rocket733]

I believe sprocket has made a key point here. Additionally most case fans are not designed to create a high static pressure, that is a difference in pressure between the intake and outtake, they are mostly designed to produce airflow and operate at a low noise.

 

[SmokeRngs]

Generally speaking, you're better off with good airflow through the case than trying to specifically design a positive or negative airflow situation. This means you want to avoid cable obstructions and dead spots around the hardware with little to no airflow. You always want good airflow around the hot components and at least some airflow anywhere a "dead spot" might accumulate heat. Along with this you need to consider air paths or air tunnels in regards to how the air is going to flow through the case. If you can setup your fans to keep air moving in a "wind tunnel" type action around the hottest components, you are more likely to exhaust most of the hot air in an efficient fashion using fewer fans and overall less noise. Depending on the case and the fans, this is probably the most difficult thing to do.

 

[Hypernova]

You don't want too much negative pressure if you get blower coolers for VGA cards. The exhaust fan and VGA fan end up fighting for air if not enough is coming in. Happens easily if you only have exhaust fans and no intake fans. Seen this happen on my P182 and 4870X2 if I turn off the front intake. Gets worse if you try and seal up the case with filters for dust control.

Positive also help VGA cool better in the above case as the VGA fan doesn't have to work as hard or if you get Acceleros which expect some air flow.

 

[E.T]

The average case, with average casefans, doesn't move enough air to build up noticeable pressure- not to mention that the average case is so riddled with holes and gaps that "pressure" couldn't be maintained, even if generated.

Yep, without fan airflow through some hole in case is decided by impedance of it and airpressure difference between inside and outside of case. So the harder working exhaust or intake fans are the higher the natural airflow through holes.

And thousand and one holes "magpie nest" cases actually need lot of both exhaust and intake fans:
If all those extra holes and gaps have roughly similar impedance then mostly air gets into case or out from it through hole/gap close to fan which is bad thing for overall cooling.

If you can setup your fans to keep air moving in a "wind tunnel" type action around the hottest components, you are more likely to exhaust most of the hot air in an efficient fashion using fewer fans and overall less noise. Depending on the case and the fans, this is probably the most difficult thing to do.

Exactly, in front in - back out configurations fans are working together for keeping up airflow but when they're everywhere in case they're mostly working alone and keeping up only short airflow loops.
Also controlled airflow enables using either just exhaust or intake fans. Just look at electric appliances/devices which use active cooling: Generally they have mostly solid case and only one fan or fans only in one end of airflow.

You don't want too much negative pressure if you get blower coolers for VGA cards. The exhaust fan and VGA fan end up fighting for air if not enough is coming in. Happens easily if you only have exhaust fans and no intake fans. Seen this happen on my P182 and 4870X2 if I turn off the front intake

Problem is high impedance plastic grill in front of intake.
Overcoming airflow decreasing effect of that impedance needs intake fan or then exhaust fans have to work harder for creating bigger pressure difference between inside and outside of case.

 

[sprocket]

This is the sort of nonsense that casemakers are fond of showing as examples of how air flows...

In my experience, this is almost completely wishful thinking.
Notice how the front fan's airstream (supposedly) turns hot after passing the hard drive cage and then finds it's way all the way to the exit grill in the back. There is one magical section however that remains cool and makes a curve upward to the CPU heatsink...it is obviously on a mission.

In real life, a hand placed behind the hard drives would probably feel little to no flow of any kind and certainly not enough to shoot all the way to the back of the case.

This particular picture also completely ignores the PSU, which is doing it's best to suck all the air from the area around the CPU heatsink- including it's fan.

I have found that trying to rely on "flow" or "airstreams" to cool components is a losing proposition.
If you want something cooled, put a fan right on it and let the "caseflow" take care of itself.
Essentially, you're relying on straight convection rather than establishment of "zones" and "streams".

The only case I've ever built that had even a modicum of "airflow" or "pressure" was this one...

( not pictured are the two intakes at the front and another on the opposite sidepanel over the vid card)
These fans were 120 x 38mm Comair Rotrons, running on 120v (wall socket) and rated at 150CFM each.
Now that case moved some air.
Was completely unbearable of course and didn't provide temps good enough to justify the aggravation.
Since I had/have no way of measuring "pressure" inside the case I don't know whether- or IF- it was balanced or tended towards "positive" or "negative".
I would guess neither.
It just moved a lot of air around.

 

[Hypernova]

Problem is high impedance plastic grill in front of intake.
Overcoming airflow decreasing effect of that impedance needs intake fan or then exhaust fans have to work harder for creating bigger pressure difference between inside and outside of case.

Or any dust filters even with fans if you want low noise. Things get worse if the PCI slots have slits and the case is against a wall or in a cabin. Hot air can get sucked back in.

 

[Santa Claus]

Then it is what i thought, need for balanced in/out fans is a myth, whats important is good airflow throughout the case.

And thousand and one holes "magpie nest" cases actually need lot of both exhaust and intake fans:

Not necessarily, i have an antec sonata with 2 speedcontroled 120mm case-fans blowing air into the case.
The case is riddled with holes but this setup was good enough to keep cpu-temps below 55celsius when i had an amd64 winchester at 2400mhz and a thermalright ultra90 with the fan disconnected.

 

[eggrock]

This is the sort of nonsense that casemakers are fond of showing as examples of how air flows...


In my experience, this is almost completely wishful thinking.
Notice how the front fan's airstream (supposedly) turns hot after passing the hard drive cage and then finds it's way all the way to the exit grill in the back. There is one magical section however that remains cool and makes a curve upward to the CPU heatsink...it is obviously on a mission.

LOL Good summary.

One thing I'm wondering about is the force applied by temperature differences. For example, if I crack open my patio door and hold a lighter in front of the door, there is a very strong outflow at the top of the door (hot air going out) and an equally strong inflow at the bottom of the door (cold air coming in). I always wondered how much that affects air in a case. Obviously it's a good indication that exhausting from the top of the case is a good idea but how much of an effect is has is the question. I think a 'good' case will only have 3-4C difference between the internal case temps and the outside air, so that probably won't generate a lot of movement (say, with a low intake in front and high exhaust in back.)

 

[timberdoodle]

LOL Good summary.

One thing I'm wondering about is the force applied by temperature differences. For example, if I crack open my patio door and hold a lighter in front of the door, there is a very strong outflow at the top of the door (hot air going out) and an equally strong inflow at the bottom of the door (cold air coming in). I always wondered how much that affects air in a case. Obviously it's a good indication that exhausting from the top of the case is a good idea but how much of an effect is has is the question. I think a 'good' case will only have 3-4C difference between the internal case temps and the outside air, so that probably won't generate a lot of movement (say, with a low intake in front and high exhaust in back.)

yea because of the low temp difference there wont be as much migration of the hot air as is from your house to the outdoors.

I always choose positive pressure to keep dust from settling inside my case, forcing the air to come through any installed filters.

 

[sprocket]

For example, if I crack open my patio door and hold a lighter in front of the door, there is a very strong outflow at the top of the door (hot air going out) and an equally strong inflow at the bottom of the door (cold air coming in). I always wondered how much that affects air in a case.

I think this would depend entirely on the temp differential.
Your example with the patio door shows that the concept is valid but is probably so noticeable because the outside air is much cooler than the room ambient.
The colder the air, the heavier it is (and the reverse is true as well), so the differential will exaggerate the effect.

It's unlikely that this extreme differential exists between the case interior and the room it's in, therefore the effect will be much less noticeable- probably not extreme enough to create the much hoped for and avidly sought "airflow" patterns as illustrated in my picture.

 

[rayra]

Just duct / arrange fans to accomodate the basic laws of thermodynamics, and to service the hottest components in your system. Put outside air right to your CPU fan. Put intakes low and towards the front. Step up exhaust fans on your PSU and rear of the case. If you make any extra fan holes, work in a blowhole / exhaust at the top of the case. And duct some coolest ouside air direct to your CPU and vid coolers.

 

[E.T]

This is the sort of nonsense that casemakers are fond of showing as examples of how air flows...
http://img.photobucket.com/albums/v78/clocker/case_airflow.jpg

In my experience, this is almost completely wishful thinking.
Notice how the front fan's airstream (supposedly) turns hot after passing the hard drive cage and then finds it's way all the way to the exit grill in the back. There is one magical section however that remains cool and makes a curve upward to the CPU heatsink...it is obviously on a mission.

You forgot to mention very high impedance hole plates for blocking exhaust holes.

 

[43st]

I've always concentrated on getting hot air out of the case. Recently, with an Antec 900 and 300 build (very open and airy designs). CPU fan pointing up > heatsink > top of case vent. I can leave all the other fans off until August/September usually.

 

[Elledan]

Ducting is definitely the best way to get air flowing across components in the right order (coolest to hottest) as well as the warmed up air out of the case. Intake fans are not required, just a clear path for the air. Look at the original PowerMac G5 for an example of how to get the air in/out really quickly and the (very hot!) hardware cool. The G5 was one hell of a hot CPU...

 

[DudeItsMe]

Ducting is definitely the best way to get air flowing across components in the right order (coolest to hottest) as well as the warmed up air out of the case. Intake fans are not required, just a clear path for the air. Look at the original PowerMac G5 for an example of how to get the air in/out really quickly and the (very hot!) hardware cool. The G5 was one hell of a hot CPU...

I haven't noticed

We have a G5 at work, along with an older Mac (I'm thinking G4, it has AGP if that helps date it), and they're back to back, about a few feet apart. Whenever I need to do something in the back of one (don't ask me why the PC guys always has to help with the Macs ), I notice the G4 is a hell of a lot hotter! I could cook behind there!

Anyways, I need to fix up my airflow... I've been doing it all wrong. Right now, the side is off of my case, because my airflow is so bad that that makes a HUGE difference.

 

[Elledan]

Well, the G5 has such excellent airflow compared to the G4 PowerMacs that the exhaust air feels much cooler for the former Just like how laptops are low-power, yet the exhaust air from some laptops (especially at load!) simply feels too hot to keep your hand near the exhaust vent

I always fear my laptop will melt if I use it for a few hours long compile session

 

[InvisiBill]

Like others have said, I think PC cases and fans generally aren't precise enough to do a whole lot of fancy stuff with pressure and airflow and such. Balancing intake and exhaust is more of a general concept to stop the idiots.

There are people out there who will fill their cases with only one or the other. They have 17 exhaust fans and wonder why it's still hot inside (because only a tiny bit of cool air creeps in through the holes and cracks in the case). Likewise, 17 intake fans doesn't do much because the hot air can't escape the case so there isn't actually much fresh air entering. While you don't need to find a way to get that 17th fan to do half intake and half exhaust to make everything match perfectly, a 9/8 or even 10/7 split would work much better than 17 of just one or the other.

Likewise, having the intakes at one end of the case and the exhausts at the other will probably create a better flow of air through the case than alternating intake and exhaust right next to each other everywhere. Unless you've got a well-designed setup with a lot of little cooling circuits, the alternating fans would probably end up just blowing a lot of the fresh air right back out, and sucking in a lot of the exhaust air - a whole bunch of air moving in little circles not really accomplishing much.