Positive or Negative Pressure?

Right now the pressure is about equal with 2 80mm pulling and another 2 pushing air.

I am thinking about putting a 120mm (63.05CFM@1800rpm) on the top of my dragon and making the 4 other 80mm as intake and possibly add one on the side for gpu.

What do you guys think?
What kind of pressure does everyone like: positive, negative, equal

Gage

Pressure, in itself, doesn't cool things. Airflow through the case does.

The only important issue involved with pressure is dust accumulation. A slightly posititve case pressure will reduce dust accumulation if the intake fans are filtered.

Adding up the max CFM rating of your intake fans, and substracting the max CFM rating of your exhaust fans, won't tell you whether you have positive or negative pressure though. Testing for a pressure differential is the only reliable way to know.

One factor that I don't often see discussed is that increased pressure will always equate to increased heat. But is this a considerable amount of heat, or is it usually too insignificant to matter?

just to make it clear Gautam, you think that more air intake will increase heat? So it's better to have more air blowing out?

Anyone else's thoughts?

Maximum airflow is the key and to do this you must have a balance of intake and outflow.

Ok, to clarify things just a bit:

In reality , with the fans and cases we use there is realy little pressure differential involved. So minute that it would be difficult or impossible to measure I think, although there is bound to be some slight difference.

When we say positive pressure about case cooling we are really referring to where that small differential exits the case: positive pressure has air leaving the case through every crack, seam and gap in the case. When done with filters (which drastically reduce airflow) this helps minimize dust in the case. You need more cfm intake then exhaust to do this. It works somewhat by all reports I have read.
Negative pressure simply means that air gets IN through all those seams and cannot be filtered.

Personally, I have two cats and I smoke (too many) cigarettes: case cleaning is something I do every three months or so and I do NOT use filters. Stuff never gets too bad either.

The real trick is getting airflow moving where it is needed: this is even more important than total cfm or "positive/negative" case pressure.

Having 300 cfm moving through your case in a straight line from front to back will NOT cool as well as 150 cfm that gets air flowing over the NB, SB and pci card area!

Personally, I usually get the best results with more exhaust than intake....

Gautam said:

One factor that I don't often see discussed is that increased pressure will always equate to increased heat. But is this a considerable amount of heat, or is it usually too insignificant to matter?

Click to expand...

I haven't done the calculations, but I suspect the rise in air temp in the case, due to higher pressure is substantially less than the temperature rise due to the power dissipation of the intake fans themselves. All the power the intake fans consume, goes into the case as heat.

thanks for the replies guys, it helps me plan out my airflow

Take a few min and use electical tape on the abundance of small holes and seams on the case to reduce dust from coming in those areas. I know that the holes in the case on the panel the MB attaches too tend to have dust marks around them indicating dust coming in from those holes. So I try to put a small peice of tape over every hole or seam I think may draw dust in.

You wont get them all but you can reduce the amount of dust with just twenty minutes or less of work.

rogerdugans said:

Ok, to clarify things just a bit:

The real trick is getting airflow moving where it is needed: this is even more important than total cfm or "positive/negative" case pressure.

Having 300 cfm moving through your case in a straight line from front to back will NOT cool as well as 150 cfm that gets air flowing over the NB, SB and pci card area!

Personally, I usually get the best results with more exhaust than intake....

Click to expand...

And the air should be removed as fast as possible from where it heated up at most I understand. Well this sounds like a tricky equation which will also involve some aerodynamics for case designers, a cube is not the ideal shape for sure.

LOL I wonder if case manufacturers will have to built wind tunnels in near future to build a case with proper airflow

The CPU is the greatest heat creater in the system, and the heat can usually be taken out of the system through a PSU with a fan on the bottom drawing air up and out.

Now that helps a great deal. So if you have a back fan drawing air in, it should pass over the HS/fan and up out the system.

Yes the PSU fan will help a great deal to take off hot air created by the heat sink. I think the real problem is the graphics card and the hard discs in fact. They produce both a lot of heat and their position in the case is rather problematic.

The graphic card is right beneath the CPU and the north bridge, both the parts we are most concerned to keep cool and the graphics card is just placed like a grill (mine does looks like a grill actually) to cook them.

And don't underestimate the hard disk especially if it is 7200 rpm or faster they produce a good amount of heat