CFM and case cooling

[Stalfos]

I want to discuss this because it could be a valuable tool for someone who is not clear when choosing fans for a certain case. This way all they would need to know is how much air they need to move against the volume of the case they choose. From there they can choose size and number with relation to the aesthetic they are aiming for.

 

Here is the question.

Mid towers with a basement usually have less than 1 CF of volume within the space where the motherboard and their components would be.

 

Not taking into account restrictions like stacked mesh filters and restrictive front panels. I believe having a 60 CFM fan on intake as well as exhaust should be sufficient to replace the volume of air within the case every second. Or at least that's what the math tells me ( on a case with 1cubic foot of volume ).

 

It sounds too good to be true in my opinion, there must be something I'm missing.

 

Now the second question is this.

If I have two fans on intake, not stacked both with 60 cfm of airflow. I have one fan on exhaust with the same 60 cfm of airflow. To my understanding I'm still only pushing 60 cfm on intake as well as exhaust. Although I have read that this could be slightly more, something like 80 CFM.

 

 

[Enderman]

1) the math is corect but the 60cfm is only with 0 restriction aa in open air, so it's actually less

 

2) assuming 0 restriction, it would be more because your 120cfm is pushing air out of the exhaust fan faster than its 60cfm can do alone, so the actual value would be somewhere between 60 and 120. Again, that's only if there was 0 restriction.

[Froody129]

I don't think it works quite like that irl. My HAF X has a ton of CFM Capacity, and I run my fans fairly hard, but there's still heat build up in the case and hotspots near the top (indicating no real low pressure to pull the air out).

 

Most would say that you want positive pressure (air in > air out) to prevent dust build up.

[Stalfos]

3 hours ago, Enderman said:

1) the math is corect but the 60cfm is only with 0 restriction aa in open air, so it's actually less

 

2) assuming 0 restriction, it would be more because your 120cfm is pushing air out of the exhaust fan faster than its 60cfm can do alone, so the actual value would be somewhere between 60 and 120. Again, that's only if there was 0 restriction.

So then you believe two 60 cfm fans actually generate 120 cfms?

[Enderman]

31 minutes ago, Stalfos said:

So then you believe two 60 cfm fans actually generate 120 cfms?

If they are in parallel, not series, in free open air, yes they do.

This is literally like putting a pencil on a weight scale.

If you put two pencils it weighs twice as much.

This is not difficult.

[Stalfos]

3 hours ago, Froody129 said:

I don't think it works quite like that irl. My HAF X has a ton of CFM Capacity, and I run my fans fairly hard, but there's still heat build up in the case and hotspots near the top (indicating no real low pressure to pull the air out).

 

Most would say that you want positive pressure (air in > air out) to prevent dust build up.

Yes, this is what I was missing. So even if you "replace" the volume of air within the case every second, there is turbulence that will occur because of the fans of the components within the case. This will cause the ambient temperature to mix with the heat generated by the components, and that will lead to a temperature difference within the case than that of ambient. That though can be included in the calculation using the tdp as an average. Though I don't think maintaining ambient within the case will be possible without having delta fan level noise. Or maybe a blower style GPU and a CPU cooler that functions like a blower directing air straight out of the case.

[Stalfos]

29 minutes ago, Enderman said:

If they are in parallel, not series, in free open air, yes they do.

This is literally like putting a pencil on a weight scale.

If you put two pencils it weighs twice as much.

This is not difficult.

Sorry, the reason I ask is because on most research I've done there seems to be two arguments. On one hand some say that two fans, in parallel, with the same capacity to move air will only move that amount of air. On the other hand some say that fans in parallel of the same capacity will increase their efficiency and create a sort of exponential growth in the capacity of air they can physically move, but by only a small amount. 

I would appreciate if you could provide additional information, links to articles or anything like that.

[Enderman]

3 minutes ago, Stalfos said:

Sorry, the reason I ask is because on most research I've done there seems to be two arguments. On one hand some say that two fans, in parallel, with the same capacity to move air will only move that amount of air. On the other hand some say that fans in parallel of the same capacity will increase their efficiency and create a sort of exponential growth in the capacity of air they can physically move, but by only a small amount. 

That's in series.

When you havce one fan in front of another.

It will increase static pressure but not airflow.

That means that at a given pressure higher than 0 there will slightly more airflow.

[Stalfos]

1 minute ago, Enderman said:

That's in series.

When you havce one fan in front of another.

It will increase static pressure but not airflow.

That means that at a given pressure higher than 0 there will slightly more airflow.

Cool, thanks.

Any thoughts about using TDP to predict average heat generated by components (not accounting for overclocking and real world heat generated) to get an idea of how much air would have to be replaced by ambient air to keep the case temp as close to ambient as audibly comfortable.

[Enderman]

1 minute ago, Stalfos said:

Cool, thanks.

Any thoughts about using TDP to predict average heat generated by components (not accounting for overclocking and real world heat generated) to get an idea of how much air would have to be replaced by ambient air to keep the case temp as close to ambient as audibly comfortable.

No, use power measurements done by reviewers, tdp isn't accurate.

There are hundreds of other variables not just cfm, you can't calculate it simply like that.

just buy good quality fans that are the noise level you want.

[Stalfos]

57 minutes ago, Enderman said:

No, use power measurements done by reviewers, tdp isn't accurate.

There are hundreds of other variables not just cfm, you can't calculate it simply like that.

just buy good quality fans that are the noise level you want.

Got it, thanks for the feedback.

[LogicalDrm]

This, ofc, is only in theory. There's no industry standard on how CFM (or CMH) fans are actually moving. Each manufacturer calculates or even markets it as their own thing. And since there's no standard, nor really testing of it by reviewers, we can't know how numbers compare between fans, or even to real world at all. Like whats the measuring distance for example.

[thrasher_565]

safe to say all marketing on the box  is un true. all of them say there fan is the best and can out perform the leading brand. and there are many different markets for the "best " fan.