positive pressure = intake CFM is MORE than exhaust CFM
negative pressure = intake cfm is LESS than exhaust CFM
points regarding positive pressure
1/ dust is not sucked into the case through the small nooks and crannies because air is going out of them.
2/
controlled dust intake with the use or good filters. this however, does not eliminate dust in the case... there will always be dust.
points regarding negative pressure
1/ air is sucked in through the nooks and crannies, and this brings dust along which means lesser control of dust intake.
2/ hot air is easily and quickly expelled out of the case, usually resulting in better overall temps.
fan RPM does not determine CFM.
so with that cleared....u need to take note of the following..
1/ aside from ur rear exhaust fan, keep in mind that ur PSU also acts as an exhaust. also, if ur GC is the type that exhausts through the back, u need to take that into account as well.
and with ur WC setup that ur planning, if ur putting the rad on top of the case, and ur gonna put the fan to blow air out, ur gonna have to add that as well.
2/ if a fan has 100cfm, take note that filters, and whatever else that blocks its airflow will reduce the cfm as well.
now...combining total CFM for both intake and exhaust each is gonna be tough. considering u have things like fangrill, filters, hdd cage, rad, bla bla bla blocking the fans airflow and reducing the CFM to an unknown amount.
so the best u can do, is forget it. seriously. temps tend to be better in a negative airflow case. also, just use all the fan slots with what theyre designed for (intake/exhaust). plus, getting positive pressure in a case is not easy.
at best, u can use low cfm fans for all the fans that are acting as exhaust and a much higher cfm fan for intakes (keeping in mind that CFM will be reduced due to blockage)
I shoulda planned this earlier on. Like there was a window side panel with 2 x 120mm fans in the sides. I thought i had sufficient cooling so i didn't need them. What i didn't think of then was regarding positive and negative pressure. So the 2 extra side fans for intake would have helped with creating sufficient positive pressure.
Oh well, guess i will need to be more diligent with cleaning my case and room from time to time
My old case i noticed buildup of dust in the crooks and crannies of the case. Also the psu and exhaust fan have lots of dust on them :/ so i know what to expect *shudder
Dec 28 2009, 08:57 PM
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I shoulda planned this earlier on. Like there was a window side panel with 2 x 120mm fans in the sides. I thought i had sufficient cooling so i didn't need them. What i didn't think of then was regarding positive and negative pressure. So the 2 extra side fans for intake would have helped with creating sufficient positive pressure.
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