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Discussion Starter · #1 ·
I was wondering if anyone could please give me some insight. I do not want this turn into a positive vs negative pressure discussion thread. What I am curious about is a few things regarding those topics. My understanding is balanced in the best option for case airflow. Wouldn't this creative stagnant airflow though ? I understand the difference between both topics, but read something that confused me. Im pulling this from the extreme tech air flow article written in 2012.

"In a positive pressure configuration, the CFM from intake fans exceeds the CFM of the exhaust fans."

"For negative, the CFM from the exhaust fans exceeds the CFM of the intake fans, creating a partial vacuum inside the case."

If this is true my question is, if I balance ( meaning same number of intake vs exhaust) out intake vs exhaust, I have generally always bought the same case fans for my entire case, meaning same speeds and cfm. From what I am seeing above, wouldn't I want even if I have balanced intake vs exhaust to have slower intake fans (cfm wise) if I want better cooling by negative pressure. I read in this article you will get more dust, but have better cooling for negative pressure.

So should I depending balanced or not and depending on the pressure I choose lower or higher cfm fans for my case. Does speed matter like cfm ? Is slower speed have lower cfm ?
 

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What offers the best results varies depending on case design type of coolers used as well as other things. There where some interesting tests done with free flow type setups which are essentially all intake fans (including thous in the top) and an open as possible back end. The idea here is that as its an full bore positive pressure setup then the rear fan actually reduces flow rather then helps it as its choking the air that wants to escape.

Basic idea looks like this.
Really if you want to go into detail about pros and cons of different flow setups you really should take a look at this thread.

http://www.overclock.net/t/1041926/how-to-decide-on-a-case-for-air-cooling-warning-pics
 

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Discussion Starter · #3 ·
Thanks but I was more curious about my question regarding cfm. I know the difference between the setups.
 

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Discussion Starter · #7 ·
Yeah, are most cases negative pressure ? I find myself frustrated trying to always get one more intake or trying to speed up intake fans. Its really hard to balance it out or get more intake. I notice most cases, and I like corsair ones lean on negative pressure. Its common to say have two front intake, top two exhaust and one rear exhaust, maybe a intake on bottom if your lucky on most medium cases. that meant say if you have a h100 i mounted on top I prefer exhaust especially on top of case that you are kind of screwed if you want positive pressure. only two intake maybe 3 if there is extra side fan or bottom mount. so you either have 3 on 3 or 2 on 3. Now you could make rear intake and have just top exhaust, but for some reason this setup looks and sounds funny to me, I have always made rear exhaust, it just makes sense to move air from front and blow out of back and top, but problem is you need great airflow from front, but this still makes negative pressure having less intake.

I guess then you are forced to have higher rpm intake fans to and lower exhaust to try and balance it out. I think airflow fans are good for exhaust, and static pressure for intake is a good idea or other way around depending on what you want. I try to actually in my setups if there is mesh or something in the way, like the radiator I use SP fans, otherwise I stick to airflow if nothing is blocking its air path to strike a good balance
 

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Don't bother about pressure, PC case not even close to impermeability, so pressure inside will be anyway equal to ambient. Bother about how much fresh air is going across videocard, it's the most important question in general.
 

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Having the same exhaust CFM as intake CFM doesn't create stagnant airflow. All the air flowing into case is flowing out and the pressure is the same inside of case as outside.
* Having a higher potential for intake CFM than exhaust caused the case to have more pressure inside than in room. * Having a higher potential for exhaust CFM than intake cause case to have slightly less pressure inside than in room.
* The important thing is to have similar vent / airflow area / CFM so the airflow into case is not being restricted because it does not have enough area / fan to exhaust as fast as it can enter, or enter as fast as it can exhaust.
* The key here is potential for because whatever air enters the case is also leaving the case .. or .. whatever air leaves the case is also entering the case. If it wasn't the case would eventually either puff up like a balloon or be sucked flat.
biggrin.gif

If intake area / fans are able to supply just a little more than the exhaust area / fans can remove, than any other holes in the case leak air out instead of in .. and no dust collects around these holes (DVD tray, I/O jacks, etc.) .. which is what happens if the exhaust potential is more than intake.

Most of us use logic and try to have just a little more potential for airflow into case than out with all intakes filtered. This means a slightly higher pressure inside of case than in room so no air is being sucked into case though unfiltered holes.

How the air flows through the case determines how close to room ambient temp the air going into coolers and to other components inside the case is. Links in sig give more info on how to setup case airflow.
 

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Discussion Starter · #10 ·
I agree slightly more intake is probably better, but I was trying to point out most cases tend to screw that up but how they are configured. More instance the 750d for example. This has the two in front and rear exhaust by design. Until you put in h100 i with sp fans as push to exhaust out. now you have 3 exhaust and only 2 intake. Which by definition is negative pressure. or more exhaust than intake. Now you can on the bottom use the extra fan mount as intake now you have 3 vs 3, but now its balanced not having more intake. Either way you are now not using the positive pressure system. Only by switching the rear exhaust to intake will you achieve a more more intake than exhaust system, and now you have to many intake. This is the frustrating thing I am not understanding why cases are set up this way. When you just told me more intake is better. When you add in a h100 i or even use the top as exhaust most usually use two fans on top for exhaust. This is what i'm trying to figure out for best airflow and best cooling.
 

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Quote:
Originally Posted by Jedson3614 View Post

I agree slightly more intake is probably better, but I was trying to point out most cases tend to screw that up but how they are configured. More instance the 750d for example. This has the two in front and rear exhaust by design. Until you put in h100 i with sp fans as push to exhaust out. now you have 3 exhaust and only 2 intake. Which by definition is negative pressure. or more exhaust than intake. Now you can on the bottom use the extra fan mount as intake now you have 3 vs 3, but now its balanced not having more intake. Either way you are now not using the positive pressure system. Only by switching the rear exhaust to intake will you achieve a more more intake than exhaust system, and now you have to many intake. This is the frustrating thing I am not understanding why cases are set up this way. When you just told me more intake is better. When you add in a h100 i or even use the top as exhaust most usually use two fans on top for exhaust. This is what i'm trying to figure out for best airflow and best cooling.
Well many would just flip the top fans for the H100 and have them suck in air form the top. Even it you now have 4 in 1 out, the air is still going to get out through the open vents in the system, plus if you have an blower style graphics card that will also exhaust air out. In some cases the PSU fan is on the inside an will also exhaust air out.

But really you are just over complicating things with trying to balance it out as it really not needed at all. It does not effect air flow that much just like stacking two fans on top of another does not increase flow.
 

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Discussion Starter · #12 ·
Yes but I have always used top as exhaust and rear as exhaust. I feel this looks better and makes sense for flow direction. I have always used h100i as exhaust on top of cases. This is what made me start this thread, and trying to unravel best airflow options. I know it will be different depending on a users setup. I just noticed that most cases traditionally have top exhaust, and rear and maybe a few intakes. This leans more towards negative pressure when, clearly people are saying more intake is better. SO why are cases set up this way ?
 

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Quote:
Originally Posted by Jedson3614 View Post

Yes but I have always used top as exhaust and rear as exhaust. I feel this looks better and makes sense for flow direction. I have always used h100i as exhaust on top of cases. This is what made me start this thread, and trying to unravel best airflow options. I know it will be different depending on a users setup. I just noticed that most cases traditionally have top exhaust, and rear and maybe a few intakes. This leans more towards negative pressure when, clearly people are saying more intake is better. SO why are cases set up this way ?
Well way back in the day the most traditional setup for any case was a single rear exhaust fan + the PSU in the top sucking air out. That's the traditional ATX layout. As hardware got hotter there was an push to move to a better flowing layout which was the BTX standard. BTX had an single intake fan that sucked air in and pushed it strait through the CPU cooler. Unfortunately BTX never really became popular so we got stuck with the ATX setup.



So as hardware continued to become hotter, case manufacturers (often inspired by case modders) started to deviate from the standard ATX case. They added in an additional front fan originally to ensure good air flow over HDD's. On larger cases that had two HDD cages each cage had its own fan, hence the 2 front fan configuration.
Other notable things was the CPU air duct that allowed stock coolers to draw in fresh air on their own. This is also where the side fans originates form but is pretty much obsolete now days.



Then somewhere in 2006-2007 (I don't really recall when it first became popular) case manufactured started putting the PSU in the bottom instead of the top. This quickly became the layout of choice. With the PSU in the bottom there was now additional room in the top and so someone got the idea to stick a fan there and have it exhaust just like the PSU fan used to do.

This lead to cases like the Antec 900, (this is 2008-2009)



It had the then popular slow spinning big top vent and a 120mm side fan.

A bit after this the first dual top fan models started hitting the market. My NZXT Tempest is form this time period. It sill isn't the modern layout we so often see today as while it had 2 top fans they where still slow spinning "vent assist" fans but it was modern in the sense that it came with air filters at stock.

After this we pretty much arrive at the modern case. Manufacturers flipped the PSU and gave it its own air filter in the bottom, which helped it become its own isolated thermal zone. The mostly useless side fan was removed form most case design while on bottom fan mounts with an filter was added to other cases. The top was made to accommodate standard fans (either 140mm or 120mm). The fact that standard fans could now be used opened up the possibility for us the end users to flip the top fans and have them intake air. As far as I know there are still no cases where the top fans comes installed as intake and people who do want to run them as intake are faced with the question of whether or not air filter them.

Case manufacturers follow the trends as much as the do their own research. The more people run top intake setups the more likely it is for manufacturer to bring that configuration to the market, just like demand for drop in 360 radiator support resulted in cases like the Switch 810 to be developed.

So why are current cases setup the way they are? To put it simply they are the evolutionary result of popular demand.

There has been cases that have truly tried to be as efficient as possible. For example the SilverStone Raven RV02 that used an all bottom to top setup with power full 180mm fans in the bottom.



But again even if this is better then most other air cooling setups you don't see many cases like this due to the lack of popular demand.
 

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Discussion Starter · #14 ·
That is a very thoughtful well answered question thank you. I for some reason prefer top mounted and rear exhaust , if more causes had more options for more front intake it would probably make for the best setup, but few do. Even monster size cases still have balance issues. Will I see a temperature hit , decline in performance, or vise versa a temp improvement or improved performance if I stick with the top and rear exhaust method, or is it so negligible that it really doesn't matter anymore. I feel though no matter how you answer, that front intake with good airflow is important , even if you have 3 vs 3 or 2 vs 3 for intake and exhaust, that dust really wont be that much of an issue and performance will still be decent.Are most cases now a days really design well enough that if you have decent fans you will have decent airflow , regardless the number of intake vs exhaust? I also don't mean that in the sense lets do all exhaust or intake, I just mean balanced wise say you have one more exhaust than intake. This whole positive pressure and negative pressure thing really throws in a wrench with cooling. I think because most want the best cooling performance as possible and its not an easy answer to answer. It really depends on your setup.
 

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Quote:
Originally Posted by Bit_reaper View Post

There has been cases that have truly tried to be as efficient as possible. For example the SilverStone Raven RV02 that used an all bottom to top setup with power full 180mm fans in the bottom.



But again even if this is better then most other air cooling setups you don't see many cases like this due to the lack of popular demand.
Sorry, but the reason we don't see more bottom to top cases is because Silverstone the patent rights on the 90 degree rotated motherboad concept.
wink.gif


Airflow area in and out need to be near equal. Fan number in and out means little.. unless all fans are identical with identical resistance, which they do not. So most people put more intake fans in to try and supply as much air as the case can flow out it's holes / vents with or without fans. This is great for some cases, but others simply do not have enough vents / holes to move the air 4x intake fans can flow into the case. What happens then is the pressure level rises in the case (too much restriction of exhaust) and fans low a large percent of their airflow .. especially if they are running at low speed.

This is why many of us now use fans designed for coolers and radiators for our case fans. They keep moving more air when the resistance increases.. It's the static pressure to airflow curve. As pressure increases flow decreases .. right up to the "static pressure" rating when air stop moving completely.

While CPU and GPU have evolved dramatically, case design has not. Bottom front to top back airlfow was fine when CPUs were 602 and GPUs were 30w TDP, but now they are 100-300w with GPU often producing twice as much heat as CPU. But cases still flow air past GPU toward CPU in most cases (no pun). This often causes high CPU temps.

Add to this the fact that GPU coolers dump air everywhere (like pancake CPU coolers) it is very hard to supply either of them with air at or very near room ambient when they are under load.

And this is why we are seeing more and more users taking the time to optimize their case's airflow.
thumb.gif
 

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Quote:
Originally Posted by doyll View Post

Sorry, but the reason we don't see more bottom to top cases is because Silverstone the patent rights on the 90 degree rotated motherboad concept.
wink.gif


Airflow area in and out need to be near equal. Fan number in and out means little.. unless all fans are identical with identical resistance, which they do not. So most people put more intake fans in to try and supply as much air as the case can flow out it's holes / vents with or without fans. This is great for some cases, but others simply do not have enough vents / holes to move the air 4x intake fans can flow into the case. What happens then is the pressure level rises in the case (too much restriction of exhaust) and fans low a large percent of their airflow .. especially if they are running at low speed.

This is why many of us now use fans designed for coolers and radiators for our case fans. They keep moving more air when the resistance increases.. It's the static pressure to airflow curve. As pressure increases flow decreases .. right up to the "static pressure" rating when air stop moving completely.

While CPU and GPU have evolved dramatically, case design has not. Bottom front to top back airlfow was fine when CPUs were 602 and GPUs were 30w TDP, but now they are 100-300w with GPU often producing twice as much heat as CPU. But cases still flow air past GPU toward CPU in most cases (no pun). This often causes high CPU temps.

Add to this the fact that GPU coolers dump air everywhere (like pancake CPU coolers) it is very hard to supply either of them with air at or very near room ambient when they are under load.

And this is why we are seeing more and more users taking the time to optimize their case's airflow.
thumb.gif
You're joking right? Christ, someone needs to go and slap the US patent office if they granted an patent for motherboard orientation. I guess Dell/alienware is next then with their 45 ° design.
 

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Quote:
Originally Posted by Bit_reaper View Post

You're joking right? Christ, someone needs to go and slap the US patent office if they granted an patent for motherboard orientation. I guess Dell/alienware is next then with their 45 ° design.
Wish I was.

Same reason why CLC coolers are not evolving. Asetek has patents on "Internal Loop Liquid" coolers' as in fareactory sealed / pump on water block and as such supplies most all CLCs out here now.


http://asetek.com/data-center/data-center-coolers/internal-loop.aspx
 

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Quote:
Originally Posted by Jedson3614 View Post

That is a very thoughtful well answered question thank you. I for some reason prefer top mounted and rear exhaust , if more causes had more options for more front intake it would probably make for the best setup, but few do. Even monster size cases still have balance issues. Will I see a temperature hit , decline in performance, or vise versa a temp improvement or improved performance if I stick with the top and rear exhaust method, or is it so negligible that it really doesn't matter anymore. I feel though no matter how you answer, that front intake with good airflow is important , even if you have 3 vs 3 or 2 vs 3 for intake and exhaust, that dust really wont be that much of an issue and performance will still be decent.Are most cases now a days really design well enough that if you have decent fans you will have decent airflow , regardless the number of intake vs exhaust? I also don't mean that in the sense lets do all exhaust or intake, I just mean balanced wise say you have one more exhaust than intake. This whole positive pressure and negative pressure thing really throws in a wrench with cooling. I think because most want the best cooling performance as possible and its not an easy answer to answer. It really depends on your setup.
Great thought. Also, many cases are designed to have large radiators on the front intake. My case has room for a 360 rad in the front intake, further hindering air flow. Not to mention that all the intake air is being heated by the radiator, filling the case with hot air. And many other cases are designed this same way. So, I agree with you, doesn't make sense.

This could be a reason why cubed and compartmentalized cases are becoming popular. By relocating radiators to separate compartments from the CPU, GPU, and board, they are in a way bypassing this issue all togehter.
 

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Discussion Starter · #19 ·
I normally just use front as intake or bottom mounts, and rear and top as exhaust, if this is horrible design for airflow then let me know, otherwise I will just continue to do it this way as I have my whole PC building career. I guessing the difference is negligible. As long as cool air is coming in from some where and exhausted out, I believe this setup is the norm for 95 % of cases.
 

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Quote:
Originally Posted by Jedson3614 View Post

I normally just use front as intake or bottom mounts, and rear and top as exhaust, if this is horrible design for airflow then let me know, otherwise I will just continue to do it this way as I have my whole PC building career. I guessing the difference is negligible. As long as cool air is coming in from some where and exhausted out, I believe this setup is the norm for 95 % of cases.
I do the exact same. I put a fan in every slot possible. Using more fans usually means I can run them at slower, quieter, speeds and still receive the same results. I put the bottom and front as intakes and the top and rear as exhaust. Just like you, I've always done it this way. I will never claim to achieve the coolest system configuration, but I have never had a system overheat or even reach what would be considered too warm either.
 
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