What's better, positive pressure airflow, or negative?

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So my case has 5 120mm case fans, 4 blow air out of the case, while only 1 is bringing anything in to the case. This creates a *negative* pressure inside the case.

Most cases I know of are the opposite, they have 2 or more fans blowing air in to the case and only 1 blowing air out of the case. This creates a *positive* pressure inside the case.

If you forget that even the best case isn't air-tight and assume that the fans are the *sole* means of air entering or exiting the case, which scenario do you think is better in terms of cooling?

 

I'm educated guessing, but I believe the cooling effect is due to the airflow generated within the case. Therefore, the higher the airflow the better.

Taking the extreme of five fans all blowing in one direction, this will build up a pressure difference within the case compared to the atmosphere and therefore the load on the fans will increase. This will have the effect of both reducing the airflow, as well as increasing the heat the fans themselves generate.

With a ratio approaching 1:1, this pressure difference doesn't occur and therefore the airflow improves.

 

I would think that 1:1 is the best way. Your hardware heats up. Thus, with air cooling, you want as much cool air as you can get to have constantly acceptable working temperatures. In that you have to think about your average surround temperature. If it is hot in your room (I know that from one LAN party or another that we had in a room under the roof in the summer) you'll need a greater airflow. The problem is that when you want to have a lot of air you either need largish and/or fast smaller fans. The obvious problem is that greater air flow results in greater noise. You have to find a balance.

I have to think about that as well right now, considering that I'll get myself that Antec P182, a two tier case.

Code:

         /\
         ||
      |--xxx------------------|      X = fans
      x                       |      
  <=  x   CPU                 |      
      x                       |      
      |                       |      
      |                       |      
      |***GPU***              |      
      |                       x      
      |                       x  <=  
      |                       x      
      |-----------------------|      
      |*****|       x  -HDD-  x      
  <=  |*PSU*|    <= x         x  <=  
      |*****|       x  -HDD-  x      
      |-----------------------|      
      

The PSU fan and the one on top and at the back will suck out air out of the case; the two front fans will suck air in, the one behind the HDD will suck air away from the HDD and blow into the case. Which, thinking of it, will create under pressure, which is probably even better than 1:1 because it will suck air through all the other openings of the case increasing the influx or relatively cool air to the computer.

Thinking of it I will probably not need the fan after the HDDs.

 

So even your case has a negative pressure inside of it since you have more fans blowing out than you have pushing in. Yeah, yeah, I know there are dozens of little holes all over the case where air can get sucked in to, which will equalize the overall pressure.

I don't think I ever seen a true 1:1 case. Even if there is one intake and one exhaust, once you add the PSU, it's unbalanced again.

That being said, remember, for the poll, it's assuming it's a sealed case with no extra ventilation holes.

 

I would say negative pressure is best. Airflow isnt enough, you need to remove hot air from the case. In any case, negative airflow means air still needs to be drawn in from the front of the case. 1:1 airflow, or even worse positive pressure, would mean that air has a chance to mill around in your case before exiting, which you dont want. You want it to blow over your components, transfer heat to itself from your components, and then exit your case.

 

I have a total of four fans in the computer; one blowing air into the side of the case, one blowing air out the back of the case, the CPU fan and one fan in the front blow air into the case. In addition I have the GPU fan which also blow hot air out of the case, some what.

If you have a good CPU fan that blows the hotair towards the back of the case it would improve airflow than the standard CPU fan.

If you have a side fan big enough to bring in cool air to the CPU, mobo chipset and GPU than it will improve airflow only if the CPU and GPU has rear case fan that remove hot air; the same theory applies to the front case fan.

Front case fans will not only help cool the CPU, GPU and chipset but most always are aimed at cooling the HDD.

The reality is to balance case cooling you need to have cool air flowing into the PC into as many components as possible and find a way to remove the hot air those components produce and from what I have seen most cases use rear and PCI ports for removal of hot air and all other locations to bring cool air into the case. There are a few execptions but most follow this rule.

I recommend flipping one of your fans to bring in some cool air if your case has a top or side fan that is currently pushing air out of the case.

 

The difference must not be to great, but a bit in favor of negative. I have 3 80 cm fans blowing in, and two blowing out, all regulated. The 120mm in the psu gives me a slight edge to negative. the 120 is regulated by the psu itself.

On the cpu a wafer cooler(ruby orb)is spinning regulated by the Mainboard. It just disperse the heat, leaving it to the casefans.

I know that the next GPU will be a two slots that takes air out.

 

@Merlanni

you don't have 80 cm fans right? i will just assume that you made a typo and that you have 8 cm fans



i am about to buy a new computer (current is a labtop) and i have been considering getting an open case, maybe putting a "hardware-store" fan next to it to give circulation i have one that doesnt make nearly as much noise as a regular computer fan, and then just have the small fans for cou gfx card and stuff like that bad idea? sry for hijacking thread

on-topic-guess i would also do a 1:1

 

Open cases are a bad idea in general. First off, you're supposed to have a controlled airflow within the case...and then there's the dust factor. If you have all the air entering through 2 or 3 fans, you can easily put a filter over them. Also, with an open case, anyone or anything can poke its nose in there and mess something up.

As for the poll...I thinking I should have left the 1:1 option off the list since it is such a rare thing to find in cases. I looked at a wide range of cases on Newegg, and every case I saw either had more fans blowing in or vice versa. I did find a *few* cases that had the same number of fans blowing in/out, but once you add the PSU, it's unbalanced again.

I'm starting to lean towards a negative pressure, because cool air will be sucked into the case wherever it can, which may cool down parts that don't normally get airflow...whereas with a positive airflow, warm air will try to escape wherever is can, and therefore possibly heat up parts.

 

A GPU can unbalance it again, if it is a double slot whit outtake.

80 mm.

How about this case? http://www.antec.com/usa/productDetails.php?id=15125&lan=us

The case cost 139 euro.

 

oh that is beautiful! how much does it cost though do you know that, couldn't pick that up

 

Negative airflow pressure causes lower air pressure inside the case, cooling it further, however it can carry less heat.

Slightly negative - one in, one plus power out - is the optimal situation, IMO, but the more power you have the closer you want it to be to 1:1 to get the maximum amount of heat removed.

And you should ALWAYS have all the fans in the front filtered and blowing air in, and have all the fans in the back blowing air out, or vice versa. Mixing in and out in a single side is never a good idea.

 

@Merlanni - Holy crap! A 250mm fan?!?! That case looks like it's designed for people who test/review system components. That case wouldn't last in any typical application...it would have a 1" layer of dust all over it in a week.

 

Wow I was just going to post a air flow question....


Got a new emachine without a case fan and I was going to put one in.
There is only a space for one in the tiny case.

http://www.emachines.com/products/products.html?prod=T5274#

I wasn't sure if that's the way it's suppose to come since I got it at an overstock outlet dirt cheap and they couldn't answer any tech Qs.

Runs very cool and probably doesn't need it now but I'm putting a second DVD drive and a Geforce 9500 PCI-e card in there along with an upgraded 430W PS.

http://www.tigerdirect.com/applications/Se...&CatId=1078

The PS has two fans and draws the air out (I have the PS in now and need to put the fan in next).

I just wanted to know if I should have the case fan draw the air in as the PS has two fans pulling the air out already or should the case fan pull the air out too?

The small case has no other large openings other than some small slot/vents and the $3 fan can go either way.
Only other fan is the CPU fan.

http://www.tigerdirect.com/applications/Se...8&CatId=494

 

If the fan opening is in the front-bottom of the case, it should be sucking air in to the case. If it's on the rear-top of the case, it should be blowing air out of the case.

 

Seems simple.
But it's the first time I've put a fan in and never had to give tought to air flow.