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Negative Pressure Filtered Intake Silicon Caulked Chassis

post #1 of 13
Thread Starter 
Is there any merit to testing this configuration? I've read it creates less stagnant air pockets, particularly around the motherboard. My HAF XB EVO has a 200mm blowing directly on the mobo but I'd love to put the glass back in and go all exhaust, then draw air in passively via the sides which are filtered. I'm likely going to test this over the weekend unless someone has damning evidence against it? Thanks in advance for any and all advice!
post #2 of 13
The inside of the case doesn't know where the air is coming from.
All that matters is how much air (CFM) is actually going through.
My System
(15 items)
 
  
CPUMotherboardGraphicsRAM
FX6300 Black M5A99X EVO R2.0 Nvidia GTS450 Team Vulcan PC3 12800 
Hard DriveOptical DriveCoolingOS
Samsung 840 PRO Asus DRW-1608P (x2) Custom Water Cooling Win7 (Ult), Win 8.1 & Win Server 2012 R2 
MonitorKeyboardPowerCase
2 X Samsung 915N Ducky Shine III, Blue Cherry/Blue LEDs PCP&C 1kw Lian Li PC-71 (W/Window) 
MouseAudio
Logiteck G400s none 
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My System
(15 items)
 
  
CPUMotherboardGraphicsRAM
FX6300 Black M5A99X EVO R2.0 Nvidia GTS450 Team Vulcan PC3 12800 
Hard DriveOptical DriveCoolingOS
Samsung 840 PRO Asus DRW-1608P (x2) Custom Water Cooling Win7 (Ult), Win 8.1 & Win Server 2012 R2 
MonitorKeyboardPowerCase
2 X Samsung 915N Ducky Shine III, Blue Cherry/Blue LEDs PCP&C 1kw Lian Li PC-71 (W/Window) 
MouseAudio
Logiteck G400s none 
  hide details  
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post #3 of 13
Quote:
Originally Posted by billbartuska View Post

The inside of the case doesn't know where the air is coming from.
All that matters is how much air (CFM) is actually going through.

And this is exactly why we don't buy sentient cases made by cats - otherwise the case would only accept tuna-filtered air. biggrin.gif

The key, as they say, is airflow, not airblow. The XB EVO is one of the best cases for clean front-to-back airflow, assuming the front intake fans are used..
post #4 of 13
Thread Starter 
Quote:
Originally Posted by billbartuska View Post

The inside of the case doesn't know where the air is coming from.
All that matters is how much air (CFM) is actually going through.

Thank you, Bill. I appreciate this sentiment and I generally agree with it because there doesn't seem to be much evidence to the contrary, but there is the occasional post or blog entry or review that describes a negative pressure system as being advantageous to the GPUs or to system cooling at the expense of dust build-up, the logical conclusion being that a filtered, sealed system would not suffer as drastically from these effects.

Am I barking up the wrong tree here? I've been googling my fingers of and I've found nothing about people doing this so it's either untried or just stupid. I'm looking for speculation here.
post #5 of 13
Looking for speculation? I speculate all day long....

I missed the part about passive intake. Is that correct? No intake fans? What about exhaust fans? What's the cooler?

With no intake fans, you will need the exhaust flow rate to be close to the cooler flow rate. The tricky bit will be if it's too low, then expect the case intake temp to increase - if the exhaust flow rate is too high, could steal air from the cooler and result again in higher temps. If this is an air cooler, then an exhaust shroud from the cooler to the rear exhaust fan would resolve some of those issues. I'd still be concerned t MB VRM cooling.

Is there a GPU in the case spraying hot air around?

This Exhaust only method seems drastic and fairly exhausting to gain at best maybe 1-2 degrees of benefit. And probably will result in higher temps. The numbers I've seen for the benefits of 'negative pressure' are in a system with slightly more exhaust than intake CFM.

However, the terms of positive vs negative pressure is more metaphor than reality. PC cases aren't really pressurized - they're far too leaky. Unless installed in a sealed propane tank. Positive/Negative pressure is best regarded as the ratio of intake CFM and exhaust CFM.

I'm skeptical about passive intake systems, from experience they run far hotter that a balanced direct airflow through a case. Still, experimenting is fun. So give it a try a report the results! (Then install some decent, quiet fans intake fans at the front and report those results).
post #6 of 13
the case has no way of knowing if the air is being pulled though or pushed through. Total CFM is not the only important fact. While total case airflow has to be equal or greater than component airflow, it is equally as important to control how and where the air flow is inside of case.

I call it airflow, not airblow
Having components that use 100cfm and a case blowing 300cfm will most likely result in lots of the component heated exhaust mixing into the cool air we want going to component intakes .. while a case flowing 125-175cfm of controlled and channeled air that keeps heated component exhaust separate from cool intake air, and flows cool air to all heat sources will give lower component temps and be quieter as well. wink.gif
post #7 of 13
Quote:
Originally Posted by MicroCat View Post

Looking for speculation? I speculate all day long....

I missed the part about passive intake. Is that correct? No intake fans? What about exhaust fans? What's the cooler?

With no intake fans, you will need the exhaust flow rate to be close to the cooler flow rate. The tricky bit will be if it's too low, then expect the case intake temp to increase - if the exhaust flow rate is too high, could steal air from the cooler and result again in higher temps. If this is an air cooler, then an exhaust shroud from the cooler to the rear exhaust fan would resolve some of those issues. I'd still be concerned t MB VRM cooling.

Is there a GPU in the case spraying hot air around?

This Exhaust only method seems drastic and fairly exhausting to gain at best maybe 1-2 degrees of benefit. And probably will result in higher temps. The numbers I've seen for the benefits of 'negative pressure' are in a system with slightly more exhaust than intake CFM.

However, the terms of positive vs negative pressure is more metaphor than reality. PC cases aren't really pressurized - they're far too leaky. Unless installed in a sealed propane tank. Positive/Negative pressure is best regarded as the ratio of intake CFM and exhaust CFM.

I'm skeptical about passive intake systems, from experience they run far hotter that a balanced direct airflow through a case. Still, experimenting is fun. So give it a try a report the results! (Then install some decent, quiet fans intake fans at the front and report those results).
To clarify,
Case intake temp will remain the same, but the component intake air temp will increase because component is using more air than case is flowing. This means component has to re-use some of it's heated exhaust resulting in higher component intake temps.



System cooling is not about how much air we can blow through a case, but about how well we supply the components with cool air and remove the heated air they give off.

Pulling air out of case has the same effect as pushing air into case. Only possible difference is how & where the air flows inside of case .. and this needs to be tuned to the needs of each build dependent on components and case used.


If you are only going to do one or the other, it is far more practical to push the air though the case than try pulling air out of case.
and I often only use intake case fans
post #8 of 13
Thread Starter 
+1 to MicroCat and doyll

@doyll
You sometimes only use intake fans? I spent most of last night watching videos and googling some more on the subject and the results seem to indicate what you're both saying, that an almost balanced flow yields the best results.

So now I'm thinking about baffling to keep airflow out of corners of the chassis and other parts where airflow isn't really needed. Any thoughts/experience with this?
post #9 of 13
Quote:
Originally Posted by Tiberiusisgame View Post

+1 to MicroCat and doyll

@doyll
You sometimes only use intake fans? I spent most of last night watching videos and googling some more on the subject and the results seem to indicate what you're both saying, that an almost balanced flow yields the best results.

So now I'm thinking about baffling to keep airflow out of corners of the chassis and other parts where airflow isn't really needed. Any thoughts/experience with this?
Have you seen my "Ways to Better Cooling" thread linked in my sig? If not, it has many of my thoughts on the hows' and whys' of airflow and cooling. I think of airflow like the water flow of a stream or river. The smoother the channel/s, the less eddies and swirls, the less chance for hot air to mix with cool air. Think of the case is a pond and the intake and exhaust as a stream or streams coming into and flowing out of the pond. The course the stream takes through the pond determines how much or little of the stream water mixes with pond water before flowing out of pond .. and the stream out of pond can only flow as much water as the stream into the pond is flowing. If we flow more out the pond will get smaller. If we flow more in the pond will get bigger. Same applies to our cases .. and obviously they don't get bigger or small so the flow in and the flow out is the same.
post #10 of 13
Thread Starter 
I have signatures turned off. Do too much mobile viewing. But I'm happy to read it if you post a link?
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