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Old 20-10-15, 07:17 AM
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case pressure airflow or SP?

if you have more 1 more fan on intake than exhaust and the exhausts are AF fans while the intakes are SP fans (combined cfm of intakes less than exhaust but SP of intake much greater than exhaust) would it still be positive case pressure based off of static pressure or would it be negative pressure based off airflow?

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Old 20-10-15, 07:33 AM
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Quote:
Originally Posted by katiekitsune View Post
if you have more 1 more fan on intake than exhaust and the exhausts are AF fans while the intakes are SP fans (combined cfm of intakes less than exhaust but SP of intake much greater than exhaust) would it still be positive case pressure based off of static pressure or would it be negative pressure based off airflow?
Asking the important questions there!

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Old 20-10-15, 11:12 PM
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bump for the reasonable time crowd
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Old 20-10-15, 11:21 PM
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Static pressure is a totally different thing altogether it's calculated by the cooling effect over a cooling surface, what you need to pay attention to here is the CFM of air the fans move and figure out how much you have entering your case and how much CFM air exiting.

More air going in than going out = Positive
More air exiting than going in = Negative
Equal air in and out = Neutral
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Old 20-10-15, 11:26 PM
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so it is CFM based not static pressure based?
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Old 20-10-15, 11:42 PM
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No CFM is the amount of air flow, static pressure is a a measure of the force of pressure the fan puts out.
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Old 21-10-15, 12:37 AM
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static pressure moves less air but can push that air through restrictions better. this is also not over a distance a sp fan with nothing in front of it wont be creating more pressure than an AF fan with nothing in front of it (all else being equal) if you were measuring it from a distance.

SP fans fins are closer together and at a different pitch. they are like this so that any air that may come back through the fan blades due to a restriction is more likely to be pushed through the restriction.
AF fans have fins spaced further apart this allows them to scoop up more air and direct it where you point the fan..

its af/sp is more a description of pushing force than a volume of air in a specified space force.

an af fan would usually be better at creating lower pressure in the case than a sp fan would be at making high pressure, because it can move more air.
this however is dependent on the resistance the AF fan would have whilst exhausting.. if it had a lot of resistance much of the air could end up back in the case.
also the cfm of a low rpm AF fan could be less than the cfm of a high rpm sp fan..

SOOO i guess the long and short of it is..
in general there are way to many variables to give you a yes or no answer.

but as you say the cfm is less for the intake than exhaust. Then it should be low pressure in the case..
However given that AF fans cfm is not measured with any resistance in front of them and not knowing how much resistance the vents give. all we can do is guess that it will probably be low pressure.
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