[SOLVED] Is Push-Pull worth it for an AIO?

Oct 1, 2020
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I've gotten some good feedback on this on Reddit, but I'd like to see what this community thinks as well.

TLDR: Is it worth it to do push/pull on an AIO rad when not using high static pressure fans and the rad is the only case intake?

OP:

Ok, so:

I'll be moving from a Dark Base 700 to a Phanteks P400A this weekend. I think I've got the fan configuration figured out, but I wanted to run it by you all here because I'm not very experienced with radiators. My GPU is on a Kraken X53 with G12 AIO bracket, and CPU will have a Kraken M22 Bequiet Pure Rock. My proposed configuration:

Front:

2x 140mm Deepcool CF140 (64.13 CFM, 1.09 mmH2O)

NZXT Kraken X63 Radiator (280mm)

2x 140mm Bequiet! Silent Wings 3 (59.5 / 101.09 CFM, 1.08 mmH2O)

Top:

2x 120mm Bequiet! Pure wings 2 ( 51.4 / 87 CFM, 1.25 mmH2O)

Rear:

1x 120mm Deepcool CF120 (56.5 CFM, 1.63 mmH2O)

NZXT Kraken M22 Radiator (120mm)



After a great deal of help/advice from u/-UserRemoved-, I am now debating between these two configs:



Front:

2x 140mm Deepcool

X63 Radiator

CPU:

2x 120mm Pure Wings 2

Top:

2x 140mm Silent Wings 3

Rear:

1x 120mm Deepcool



Front:

2x 140mm Deepcool

X63 Radiator

2x 140mm Silent Wings 3

CPU:

1x 120mm Pure Wings 2

Top:

1x 120mm Pure Wings 2

Rear:

1x 120mm Deepcool



Other components:

Ryzen 5 3600 (no OC)

RX 590 (w/ Kraken G12 kit)

MSI B450 Gaming Pro Carbon WiFi

2x 8gb Vengeance 3000

Phanteks P400A



Which of these setups would you go with, and why?
 
I'm always up for learning. What should I Google?
PC Fan mfg never really publish these graphs. But here goes...

To understand how any fan performs, you have to look at it's RPM and it's static pressure. Static pressure is the "resistance" to airflow. So if you have a lot of things interfering with the flow (meshes/grills etc), that static pressure will go up.


The red lines represent the fan RPM. The exponential curve to the left is the cut off zone. Anything to the left of that exponential line is the "no run zone" and it's data should be ignored as you can't use a fan in this area.

So let's take a fan and run it at 1350 RPM. With a near 0 static pressure (0 axis) you get ~8300 m^3 / hour of air

But if you increase the static pressure to 475Pa your airflow drops to ~4500m^3/hr. @ 1350RPM.

So now we can see how static pressure reduces airflow.

Now let's take two formulas.

Force of Drag = .5 * Coefficient of Drag * Face Area * air flow velocity^2 (https://en.wikipedia.org/wiki/Drag_(physics)#Aerodynamics )

The more blockages you put into that air path, the higher the Coefficient of drag will be. As you picked out a fan which focuses on high air flow velocity, your drag will be exponentially higher. As a result your static pressure will also be higher, the faster you have to run your fans to achieve the same airflow.

A lot of drag force gets transformed into noise and heat.

With fans that are high static pressure designs (Fewer but larger sweeping blades) you get a higher static pressure at lower RPMs and the pressure drop curve isn't nearly as steep.

Now onto Bernoulli's

P1 = P0 - 1/2pv*v (Simplified for low speed air)

This is the principal behind aircraft propellers, and airplane flight in general and how they generate thrust. Moving air "weighs" less and it creates a pressure differential which generates thrust. The air on the top of a wing/airfoil/prop weighs less than the air beneath/behind it.

This describes the pressure difference between moving air and non moving (static air) https://en.wikipedia.org/wiki/Bernoulli's_principle

So you have a greater pressure differential the faster your airflow will be. This leads to greater resistance overall.

Now when you create a push OR pull configuration, you are working against atmospheric pressure as well as surface friction. When you create and PUSH AND PULL configuration, the pressure differential between surfaces is LESS, thus the fan doesn't have to fight atmospheric pressure till the pull fan vents the air to atmosphere. Thus the pushing fan doesn't have to work as hard to push that air because there is a less of a static pressure differential in that gap.

Make sense?
 
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Phaaze88

Glorious
Ambassador
The purpose of push-pull is being able to run the fans at lower rpms, thus less noise, the purpose is not actually for cooling.

With a P400A, a push-pull here would be just for show; the Kraken's fans can take care of cooling on its own.
 
Oct 1, 2020
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The purpose of push-pull is being able to run the fans at lower rpms, thus less noise, the purpose is not actually for cooling.

With a P400A, a push-pull here would be just for show; the Kraken's fans can take care of cooling on its own.

I won't be using the Kraken Aer P fans for the rad, it'd be either Deepcool CF140s or CF140s (push) + Silent Wings 3 (pull)
 
Oct 1, 2020
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I think Push/Pull is ESPECIALLY useful when you DON'T have static pressure optimized fans.

Rads are VERY airflow restrictive, especially as the fan speeds increase.
I agree, that's my thinking as well. Do you think though that push-pull would help with case airflow vs just push? I'd assume it couldn't hurt since then there'd be one pair of fans pulling air from the rad and blowing it (unrestricted) into the case
 
Oct 1, 2020
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Just curious - why not?
Mainly acoustics. The Aer P's are a good 10-15 dB louder iirc. I've got two of them in my current build as case fans (bad idea, I know) and they're definitely the loudest parts in the system. I'm using a DB700 right now so if they're loud in there I don't even want to try in a mesh-front case like the P400A. Also, something to bear in mind: I won't be able to see into the case at all, so visual appearance is not a concern. I'm mainly going for quiet operation and decent case thermals.
 
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Phaaze88

Glorious
Ambassador
Dark Base 700 is more restrictive by design, so you have to 'brute force' air in a chassis like that to get more reasonable thermals.
With the P400A, you don't need to run Aer P at 100%, or very high at all.
Oh well.
 
Oct 1, 2020
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Dark Base 700 is more restrictive by design, so you have to 'brute force' air in a chassis like that to get more reasonable thermals.
With the P400A, you don't need to run Aer P at 100%, or very high at all.
Oh well.
Aer P: 21~38dBA

CF140: 19.8~24dB

Silent Wings 3: ?~15.5

I would assume that having the quieter fans running in push/pull (lower RPM) would be quieter than the Aer P's alone (low-mid RPM) since they wouldn't have to run as high, even though the Aers have higher SP. Even at the lowest allowable speed with Argus Monitor, (40%) the Aer P's are noticeably louder than any other fans in my system.
 
I've gotten some good feedback on this on Reddit, but I'd like to see what this community thinks as well.

TLDR: Is it worth it to do push/pull on an AIO rad when not using high static pressure fans and the rad is the only case intake?

OP:

Ok, so:

I'll be moving from a Dark Base 700 to a Phanteks P400A this weekend. I think I've got the fan configuration figured out, but I wanted to run it by you all here because I'm not very experienced with radiators. My GPU is on a Kraken X53 with G12 AIO bracket, and CPU will have a Kraken M22 Bequiet Pure Rock. My proposed configuration:

Front:

2x 140mm Deepcool CF140 (64.13 CFM, 1.09 mmH2O)

NZXT Kraken X63 Radiator (280mm)

2x 140mm Bequiet! Silent Wings 3 (59.5 / 101.09 CFM, 1.08 mmH2O)

Top:

2x 120mm Bequiet! Pure wings 2 ( 51.4 / 87 CFM, 1.25 mmH2O)

Rear:

1x 120mm Deepcool CF120 (56.5 CFM, 1.63 mmH2O)

NZXT Kraken M22 Radiator (120mm)



After a great deal of help/advice from u/-UserRemoved-, I am now debating between these two configs:



Front:

2x 140mm Deepcool

X63 Radiator

CPU:

2x 120mm Pure Wings 2

Top:

2x 140mm Silent Wings 3

Rear:

1x 120mm Deepcool



Front:

2x 140mm Deepcool

X63 Radiator

2x 140mm Silent Wings 3

CPU:

1x 120mm Pure Wings 2

Top:

1x 120mm Pure Wings 2

Rear:

1x 120mm Deepcool



Other components:

Ryzen 5 3600 (no OC)

RX 590 (w/ Kraken G12 kit)

MSI B450 Gaming Pro Carbon WiFi

2x 8gb Vengeance 3000

Phanteks P400A



Which of these setups would you go with, and why?
This is a very complex question for which there is no clear cut answer because there are too many variables.

I was going to go into a long diatribe as an engineer, and use a bunch of formulas to describe the issue. But then I didn't want to over do it. (I have a tendency to ramble)

But to summarize:
Yes, a push pull will help. However using suboptimal fans in the first place (high airflow) will result in more noise than necessary as they will have to ramp higher to get the same airflow mass. But this all depends on the model fans and what their fan curves look like. And this varies from mfg to mfg.
 
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Phaaze88

Glorious
Ambassador
Those are the noise levels at 100%. How many people regularly run their fans at that speed?
There's different fan curves between models... manufacturers don't even post fan curves online, save for like 2 of them.
Performance and noise doesn't scale linearly...

Anyway, the point's been made, so...
But to summarize:
Yes, a push pull will help. However using suboptimal fans in the first place (high airflow) will result in more noise than necessary as they will have to ramp higher to get the same airflow mass. But this all depends on the model fans and what their fan curves look like. And this varies from mfg to mfg.
Oh! I like this one!
 
Oct 1, 2020
12
0
10
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This is a very complex question for which there is no clear cut answer because there are too many variables.

I was going to go into a long diatribe as an engineer, and use a bunch of formulas to describe the issue. But then I didn't want to over do it. (I have a tendency to ramble)

But to summarize:
Yes, a push pull will help. However using suboptimal fans in the first place (high airflow) will result in more noise than necessary as they will have to ramp higher to get the same airflow mass. But this all depends on the model fans and what their fan curves look like. And this varies from mfg to mfg.
I would not be at all opposed to an Engineer-level summary of this issue. I doubt I'd understand it fully, but I've been focused on this issue for long enough now that I think it's time for science. The fans used in place of the Aer P's would be the Deepcool Cf140's (https://www.deepcool.com/product/dcoolingaccessory/2018-05/12_8346.shtml) in push, and the BeQuiet Silent Wings 3 140's (https://www.bequiet.com/en/casefans/717) in push. BQ gives a fan curve, but I don't think Deepcool does. I don't really understand how the curves correlate to real-world, so if you'd like to give a brief explanation of that, I'd appreciate it.

What I'm really struggling to understand is how the Aer P's could possibly be quieter under any condition, given that their dB minimum is just barely lower than the maximum for the airflow fans.
 
Oct 1, 2020
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Those are the noise levels at 100%. How many people regularly run their fans at that speed?
There's different fan curves between models... manufacturers don't even post fan curves online, save for like 2 of them.
Performance and noise doesn't scale linearly...

Anyway, the point's been made, so...

Oh! I like this one!
Aer P: 21~38dBA

CF140: 19.8~24dB

Silent Wings 3: ?~15.5

I believe the dB levels given are a range, save for the BQ fans, which I believe is showing only the maximum. (this would make sense, as I can barely hear these fans at all at 100% speed). I understand that the non-SP-optimized fans would have to run higher rpm to perform the same as the Aer P's, but even at max rpm they're much quieter, so I don't understand how they could possibly be louder. DB scale is logarithmic, so 4 fans at 20dB should be quieter than 2 fans at 30dB. I just don't know if that's typically the case in real-world use due to other variables.
 
I would not be at all opposed to an Engineer-level summary of this issue. I doubt I'd understand it fully, but I've been focused on this issue for long enough now that I think it's time for science. The fans used in place of the Aer P's would be the Deepcool Cf140's (https://www.deepcool.com/product/dcoolingaccessory/2018-05/12_8346.shtml) in push, and the BeQuiet Silent Wings 3 140's (https://www.bequiet.com/en/casefans/717) in push. BQ gives a fan curve, but I don't think Deepcool does. I don't really understand how the curves correlate to real-world, so if you'd like to give a brief explanation of that, I'd appreciate it.

What I'm really struggling to understand is how the Aer P's could possibly be quieter under any condition, given that their dB minimum is just barely lower than the maximum for the airflow fans.
Well this is a proper fan curve graph. And to understand what I'm about to teach you, you have to know how to read it. Are you up for that?

 
I'm always up for learning. What should I Google?
PC Fan mfg never really publish these graphs. But here goes...

To understand how any fan performs, you have to look at it's RPM and it's static pressure. Static pressure is the "resistance" to airflow. So if you have a lot of things interfering with the flow (meshes/grills etc), that static pressure will go up.


The red lines represent the fan RPM. The exponential curve to the left is the cut off zone. Anything to the left of that exponential line is the "no run zone" and it's data should be ignored as you can't use a fan in this area.

So let's take a fan and run it at 1350 RPM. With a near 0 static pressure (0 axis) you get ~8300 m^3 / hour of air

But if you increase the static pressure to 475Pa your airflow drops to ~4500m^3/hr. @ 1350RPM.

So now we can see how static pressure reduces airflow.

Now let's take two formulas.

Force of Drag = .5 * Coefficient of Drag * Face Area * air flow velocity^2 (https://en.wikipedia.org/wiki/Drag_(physics)#Aerodynamics )

The more blockages you put into that air path, the higher the Coefficient of drag will be. As you picked out a fan which focuses on high air flow velocity, your drag will be exponentially higher. As a result your static pressure will also be higher, the faster you have to run your fans to achieve the same airflow.

A lot of drag force gets transformed into noise and heat.

With fans that are high static pressure designs (Fewer but larger sweeping blades) you get a higher static pressure at lower RPMs and the pressure drop curve isn't nearly as steep.

Now onto Bernoulli's

P1 = P0 - 1/2pv*v (Simplified for low speed air)

This is the principal behind aircraft propellers, and airplane flight in general and how they generate thrust. Moving air "weighs" less and it creates a pressure differential which generates thrust. The air on the top of a wing/airfoil/prop weighs less than the air beneath/behind it.

This describes the pressure difference between moving air and non moving (static air) https://en.wikipedia.org/wiki/Bernoulli's_principle

So you have a greater pressure differential the faster your airflow will be. This leads to greater resistance overall.

Now when you create a push OR pull configuration, you are working against atmospheric pressure as well as surface friction. When you create and PUSH AND PULL configuration, the pressure differential between surfaces is LESS, thus the fan doesn't have to fight atmospheric pressure till the pull fan vents the air to atmosphere. Thus the pushing fan doesn't have to work as hard to push that air because there is a less of a static pressure differential in that gap.

Make sense?
 
Last edited:
Reactions: thefxgamingrules
Oct 1, 2020
12
0
10
0
PC Fan mfg never really publish these graphs. But here goes...

To understand how any fan performs, you have to look at it's RPM and it's static pressure. Static pressure is the "resistance" to airflow. So if you have a lot of things interfering with the flow (meshes/grills etc), that static pressure will go up.


The red lines represent the fan RPM. The exponential curve to the left is the cut off zone. Anything to the left of that exponential line is the "no run zone" and it's data should be ignored as you can't use a fan in this area.

So let's take a fan and run it at 1350 RPM. With a near 0 static pressure (0 axis) you get ~8300 m^3 / hour of air

But if you increase the static pressure to 475Pa your airflow drops to ~4500m^3/hr. @ 1350RPM.

So now we can see how static pressure reduces airflow.

Now let's take two formulas.

Force of Drag = .5 * Coefficient of Drag * Face Area * air flow velocity^2 (https://en.wikipedia.org/wiki/Drag_(physics)#Aerodynamics )

The more blockages you put into that air path, the higher the Coefficient of drag will be. As you picked out a fan which focuses on high air flow velocity, your drag will be exponentially higher. As a result your static pressure will also be higher, the faster you have to run your fans to achieve the same airflow.

A lot of drag force gets transformed into noise and heat.

With fans that are high static pressure designs (Fewer but larger sweeping blades) you get a higher static pressure at lower RPMs and the pressure drop curve isn't nearly as steep.

Now onto Bernoulli's

P1 = P0 - 1/2pv*v (Simplified for low speed air)

This is the principal behind aircraft propellers, and airplane flight in general and how they generate thrust. Moving air "weighs" less and it creates a pressure differential which generates thrust. The air on the top of a wing/airfoil/prop weighs less than the air beneath/behind it.

This describes the pressure difference between moving air and non moving (static air) https://en.wikipedia.org/wiki/Bernoulli's_principle

So you have a greater pressure differential the faster your airflow will be. This leads to greater resistance overall.

Now when you create a push OR pull configuration, you are working against atmospheric pressure as well as surface friction. When you create and PUSH AND PULL configuration, the pressure differential between surfaces is LESS, thus the fan doesn't have to fight atmospheric pressure till the pull fan vents the air to atmosphere. Thus the pushing fan doesn't have to work as hard to push that air because there is a less of a static pressure differential in that gap.

Make sense?
You lost me on the formulas, but I think I understand the concept of the principles. So I would assume that a fan's SP rating is actually it's ability to overcome static pressure? Or is it the amount of SP generated by the fan itself? And as far as drag force, am I thinking correctly that the airflow fans would be louder than the SP fans because they'd actually be moving too MUCH air?

I'm confident at this point that the CF140s in tandem with the Silent Wings 3 will generate enough SP to cool the rad effectively and hopefully still provide some good case airflow. Theoretically, they should only give about 30% less SP than the Aer Ps (if I'm understanding mfg given specs correctly), and even at low RPM these fans are much louder than both the CF140s and Silent Wings 3 at close to full speed. So airflow aside, this config would likely also result in less noise, unless all four fans wind up needing to run close to max RPM, and even then we're talking ~3dB louder than the Aer P's at minimum speed. Are you saying that this wouldn't matter in real-world application because of the air being forced through the rad and mesh, creating drag force?

Also of note:
The BQ fans have 7 blades (same as Aer P) but they are a different shape.
I can't find anything on what different blade shapes are actually called, but they appear to me to be more "sweeping" than the Aer P blades, which are flat and straight, rather than curved.
 
You lost me on the formulas, but I think I understand the concept of the principles. So I would assume that a fan's SP rating is actually it's ability to overcome static pressure? Or is it the amount of SP generated by the fan itself?
The fan generates a static pressure differential. This is what makes air move/flow. To have airflow, the fan has to be able to generate a static pressure (thrust) that is greater than the resistance static pressure (drag). The bigger the differential between thrust and drag, the better the airflow. By putting a fan in push pull, you are reducing the thrust/drag difference in that gap between the fans. But you are also getting more fan noise because you have twice the fans.

And as far as drag force, am I thinking correctly that the airflow fans would be louder than the SP fans because they'd actually be moving too MUCH air?
Well yes and no. You can get higher airflow with high velocity fans. But that's only in free airflow situations. Their flow rate drops off more dramatically the more static pressure resistance they face. Excess airflow velocity does generate a lot more noise than a high static pressure lower airflow fan. It's a balancing act.

I offered to teach Steve @ GN how to set this up in a lab environment and create fan graphs to analyze these things for case airflow, but he never replied back. This is all first year Aero engineering stuff.

This along with Newtons law of thermodynamic cooling explains why big surface area/thin radiators are usually superior to thick or high fin density radiators. (That's 1st year thermo)
 
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Oct 1, 2020
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The fan generates a static pressure differential. This is what makes air move/flow. To have airflow, the fan has to be able to generate a static pressure (thrust) that is greater than the resistance static pressure (drag). The bigger the differential between thrust and drag, the better the airflow. By putting a fan in push pull, you are reducing the thrust/drag difference in that gap between the fans. But you are also getting more fan noise because you have twice the fans.



Well yes and no. You can get higher airflow with high velocity fans. But that's only in free airflow situations. Their flow rate drops off more dramatically the more static pressure resistance they face. Excess airflow velocity does generate a lot more noise than a high static pressure lower airflow fan. It's a balancing act.

I offered to teach Steve @ GN how to set this up in a lab environment and create fan graphs to analyze these things for case airflow, but he never replied back. This is all first year Aero engineering stuff.
Wow. This is quite the revelation.

So, realistically, I can ignore all tests/reviews/benchmarks regarding push-pull that use an open-air environment. (Which is most of them) Looks like I may wind up having to actually test out multiple different configs instead of getting a magic answer from the internet!

Thank you so much for all your help! With these explanations I can at least put my mind at ease until the new case comes in. I'll probably go with push/pull with the airflow fans initially, and if it seems loud it'd be easy enough to swap the fans out.
 

Phaaze88

Glorious
Ambassador
Looks like I may wind up having to actually test out multiple different configs instead of getting a magic answer from the internet!
That's exactly what I did... and what I found out in my particular setup, is that I don't need any exhaust fans - they actually make things a little worse.
I wasn't aiming for a push-pull intake at all - it just happened to work out that way; the radiator tubes weren't long enough to allow me to mount the thing up top.

It's too bad there's so many of these 'best fan setup', etc, type threads out there, because the actual answer is going to vary for everyone.
So unless they have a NZXT H500 or something, I'll just tell them to do a 'front to back, bottom to top' if they can't be bothered to do their own testing.
 

USAFRet

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Wow. This is quite the revelation.

So, realistically, I can ignore all tests/reviews/benchmarks regarding push-pull that use an open-air environment. (Which is most of them) Looks like I may wind up having to actually test out multiple different configs instead of getting a magic answer from the internet!

Thank you so much for all your help! With these explanations I can at least put my mind at ease until the new case comes in. I'll probably go with push/pull with the airflow fans initially, and if it seems loud it'd be easy enough to swap the fans out.
If push/pull were a default great benefit, to either temps or noise, more systems would be designed like that from the start.
 
Oct 1, 2020
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That's exactly what I did... and what I found out in my particular setup, is that I don't need any exhaust fans - they actually make things a little worse.
I wasn't aiming for a push-pull intake at all - it just happened to work out that way; the radiator tubes weren't long enough to allow me to mount the thing up top.

It's too bad there's so many of these 'best fan setup', etc, type threads out there, because the actual answer is going to vary for everyone.
So unless they have a NZXT H500 or something, I'll just tell them to do a 'front to back, bottom to top' if they can't be bothered to do their own testing.
Hmm.. So in theory the exhaust fans were creating more negative pressure inside the case, making it even harder for the front intakes to overcome that pressure to bring fresh air in?
 

Phaaze88

Glorious
Ambassador
Weird. I'll give it a go with no top exhaust. I wouldn't have even thought to remove that had you not mentioned it.
I tried a number of configurations alongside the usual front to back, including:
-3 top intake
-2 top intake: the front and middle
-1 top intake: front only
-2 top exhaust: the middle and rear
-1 top exhaust: rear only
-top-front intake and top rear exhaust
Nope, nothing I did overcame just having those fans in the front. That was the best for cpu and gpu thermals overall.
 

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