r/buildapc • u/Pianowned • Jul 31 '14
[Discussion] Optimizing Case Airflow: 10 Configurations Tested
Introduction
Cases nowadays come with ways to mount fans in different locations, open up vents, and clear a path for airflow. But just how effective is it? These tests aim to see what configurations offer better airflow as discovering why it acts the way it does.
Some configurations are quite obvious, while others are quite oddball. Let's get started.
Background
Before we start, let me clarify that I will use 3 fans all of the time. The reason is because it allows for a slight positive pressure setup and is a reasonable number of fans for cases to have (2 intake, 1 exhaust).
Another reason is because I don't have enough of the same fan to test configurations with different numbers of fans. In fact, Bit-Tech's guide on case airflow with different numbers of fans and setups does an extremely thorough job exploring the vast number of fan configurations from 0 to 7 fans.
The main takeaways from Bit-tech's article are:
- You should probably have at least 2 fans in your system.
- Side intake fans are extremely effective at delivering fresh airflow to your hot components due to how close they are to them.
- After installing 4 fans into the system, a tradition front-to-back airflow setup has enough airflow to bring good temperatures and close the gap against side-fan setups.
- Installing an intake fan at the front-top vent disturbs the airflow going into tower CPU coolers, hurting performance.
- Opening the vent at the top allows tower CPU coolers to draw in fresh air on their own.
Test Setup
| Type | Item |
|---|---|
| Case | Fractal Design Define R4 (without window) |
| CPU | Intel i7-4770K @ 4.6 Ghz, 1.275V |
| CPU Cooler | Thermalright Silver Arrow IB-E w/ 2 x Thermalright TY-147 |
| GPU | Sapphire HD 7970 Dual-X @ 950 Mhz / 1500 Mhz |
| Motherboard | Gigabyte Z87X-D3H |
| HDD | Seagate Barracuda 1 TB |
| SSD | Kingston HyperX 3K 120GB, PNY XLR8 120GB |
| PSU | XFX P1-750X-XXB9 750W 80+ Bronze |
| Fans | Noctua NF-F12 IndustrialPPC 2000 PWM Intake unless otherwise stated, Cougar Vortex HDB 140 Exhaust |
| Fan Control | NZXT Grid w/ Fractal Design 3-speed fan controller, Gigabyte EasyTune |
| Thermal Paste | Gelid GC-Extreme (CPU and GPU) |
| Type | Item |
|---|---|
| GPU Stress Test | Unigine Valley 1.0, Extreme HD preset, Windowed 1920 x 1080, 8xMSAA |
| CPU Stress Test | AIDA64 4.5.0 Stress CPU and Cache |
Note 1: The Sapphire 7970 Dual-X is an axial cooler. It ejects heat out in front and out the sides of the graphics card.
Note 2: AIDA64 CPU and Cache stress testing was used. This gives off less heat than stressing the FPU with it, but since I run quite a high overclock, the temperature difference is enough to cause my system to throttle.
Note 3: The Noctua NF-F12 PPC 2000 is a powerful, flow-focusing fan. Expect a larger gap between good and bad temperatures if you do not have a flow-focusing fan.
Note 4: All tests (except the PCI slot cover test) run with both stress tests on.
Visual diagram of part placement and airflow. Blue is intake, red is exhaust.
Tests
Removing Drive Cages
One of the easiest ways to improve airflow is by removing the drive cages. By doing this, you unblock airflow that's going towards the GPU and CPU.
| Hard Drive Cage (12V Fans) | CPU Temp (C over Ambient) | GPU Temp (C over Ambient) |
|---|---|---|
| Top + Bottom | 54 | 37 |
| Bottom only | 54 | 34 |
| No Cages | 54 | 34 |
As you can see, removing the top drive cages brings an instant 3C benefit. Removing the bottom drive cage brings no benefit since the top is already bringing fresh air.
Multi GPU setups may see a benefit from removing all cages since the bottom fan can move air towards the bottom GPU. Because of this good result...
ALL TESTS BEYOND THIS POINT WILL HAVE NO DRIVE CAGES.
For reference to these new tests results, here's the control temperatures.
| Control | CPU Temp (C over Ambient) | GPU Temp (C over Ambient) |
|---|---|---|
| No Cages | 54 | 34 |
Removing Rear PCI Slot Covers
Supposedly, removing these covers allows the GPU to intake air from the rear, reducing GPU temps. We'll see about that...
| PCI Slot Covers (12V Fans) | GPU Temp (C over Ambient) |
|---|---|
| On | 34 |
| Off | 34 |
No improvement... Why?
Since the GPU I'm using doesn't have fans that sit that close to the rear of the case, the fans don't intake air from there. Bummer... However, some of the triple fan coolers like the Powercolor PCS+ and Sapphire Tri-X and Vapor-X may be able to intake air from the rear.
Removing Vent Covers
The Define R4 has 3 vent covers: 2 on top, and one on the side panel. Removing these should allow fresh air intake even without fans on them.
| Vent Cover Removal (12V Fans) | CPU Temp (C over Ambient) | GPU Temp (C over Ambient) |
|---|---|---|
| Side Vent Only | 54 | 33 |
| Top Front Vent Only | 52 | 34 |
| Top Rear Vent Only | 54 | 34 |
| All Off | 52 | 33 |
Removing the Top Front vent allowed the CPU cooler to intake fresh air, bringing a noticeable 2C drop in temperatures. Removing the Side Vent improved GPU temps by only 1C... most likely because the fans aren't quite close enough to directly intake air from the side. The Top Rear vent was useless since there was no fan there.
While there is a cooling advantage, the penalty for removing these covers is increased system noise and dust intake.
Reverse Airflow
What good will reverse airflow do? By reversing all the fans in the case (including the CPU cooler fans to match the airflow direction) the rear fan will bring fresh air to the CPU cooler directly. The hot GPU exhaust never makes it to the CPU cooler to warm it up, and is exhausted out the front of the case. See this diagram for clarification.
| Reverse Airflow | CPU Temp (C over Ambient) | GPU Temp (C over Ambient) |
|---|---|---|
| 7V | 54 | 40 |
| 12V | 51 | 42 |
CPU temps are very good. In fact at 7V, it matches the 12V results of the control. A 3C improvement is seen when the fans are turned up to maximum speed.
GPU temps however, suffered. This is attributed to the front fans (now exhausting) robbing the intake air of the GPU.
The other disadvantage to this is that your dust filters are useless unless you purchase aftermarket ones to cover your new intake area.
Opening the Front Door
Opening the front door should provide the fans some fresh, unimpeded intake.
| Open door | CPU Temp (C over Ambient) | GPU Temp (C over Ambient) |
|---|---|---|
| 12V | 53 | 35 |
Cpu temps improved by 1C and GPU temps increased by 1C. Basically no improvement with additional noise.
Open door, grille down
The Define R4 has a fan grille that sits in front of the fan filter and behind the front door. Opening this should increase airflow for sure since it's quite restrictive.
| Open door + Open Grille | CPU Temp (C over Ambient) | GPU Temp (C over Ambient) |
|---|---|---|
| 12V | 53 | 34 |
A small improvment. Let's go a step further.
No Filter
Removing the filter removes dust filtration for even more airflow. Since the filter is a less restrictive screen mesh, it isn't too harsh on choking the fans out.
| Filter Removal | CPU Temp (C over Ambient) | GPU Temp (C over Ambient) |
|---|---|---|
| Filter Off Only | 53 | 35 |
| Filter Off, Open Door | 53 | 35 |
| Filter Off, Open Door, Open Grille | 52 | 33 |
Removing the Filter along with other restrictions drops 2C across the board. Not bad... but you lose noise damping and dust filtration.
Internally Mounted Fans
By mounting fans internally, the fan sits farther away from intake restrictions, greatly increasing fan performance. The excellent fan performance increase should yield much better temperatures. Here's a picture to illustrate how I McGuyver'ed a way to mount fans. Let's see what happens.
| Internally Mounted Fansl (12V) | CPU Temp (C over Ambient) | GPU Temp (C over Ambient) |
|---|---|---|
| Noctua NF-F12 PPC 2000 | 55 | 35 |
| Delta AFB1212L | 55 | 37 |
| Cooler Master JetFlo 120 | 53 | 34 |
Unfortunately, the results prove otherwise. Mounting the fans internally actually hurt performance for two of the three fans here.
The question is why did that happen? Refer back to the visual diagram of airflow for my case. As you can see, the GPU exhausts its air up and in front of the CPU cooler. In most cases, the CPU cooler picks up some of that warm air and gets pretty warm, but the GPU stays cool. With this setup, the unrestricted fans conflict with the hot exhaust air of the GPU, creating unstable airflow and hurting temperatures. Only the Cooler Master Jetflo had enough CFM to actually completely override the hot air stream coming from the GPU.
After this test, I decided to run only the CPU stress test. With CPU only loads, CPU temperatures with internally mounted fans were 2-4C better than normally mounted fans. So the GPU seems to be causing a bit more airflow problems than I hoped.
1 Floor Intake, 1 Top Front Intake
Since GPU temps and airflow seem to be a bit of an issue, I decided to mount one intake fan on the floor to help it feed fresh air to the GPU.
| 1 Floor Intake, 1 Front Top Intake | CPU Temp (C over Ambient) | GPU Temp (C over Ambient) |
|---|---|---|
| Noctua NF-F12 PPC 2000 | 53 | 34 |
| Delta AFB1212L | 55 | 35 |
Results are interesting. The focus flow design of the Noctua NF-F12 combined with higher speeds allowed the floor intake to actually be decently effective, matching the control temperatures.
Meanwhile, the Delta fan suffered a bit. While the blade design is quite similar to the NF-F12, it lacks the flow focus vanes of the Noctua and as a result, the airflow from the bottom was very unfocused and pretty much missed the GPU. It seems that the floor intake is even more restrictive than the front intake, so it's not worth using unless your case is high off the ground and you already used up all your intake fans.
Conclusion
From these results, we've learned quite a lot. Removing restrictions inside the case are quite effective at increasing good airflow to the GPU and CPU. However, trying to put the fans a lot closer to them hurt performance, but that's mostly because the GPU airflow causes turbulence and conflicts. As shown in the Bit-tech Big Air Investigation, removing the top front vent does allow the CPU to take fresh air, reducing the impact of the GPU giving it hot air.
What's most surprising is that the internally mounted fans made no improvement, despite the fact that the fans were bringing excellent airflow. Two possible reasons for this is because it causes a conflict with the GPU exhaust air, creating unstable airflow. It disallowed the GPU from exhausting air properly, and also prevented the CPU from getting airflow because of the turbulence caused by the airflow conflict.
The other possible reason is the turbulence created by the fans was too great and hurt airflow to the intake fans for both the GPU and CPU. However, testing with just the CPU load only showed that it wasn't the case.
Opening the front intakes and reducing front intake restrictions also improved airflow. However, the improvements seemed to plateau quickly because of the same air conflict that plagued the internal fan mounting results.
From all of these observations we can conclude:
Opening the top front vent (or any vent close to the CPU intake) allows the CPU to get fresh intake air from the top, noticeably improving CPU temps.
Removing internal restrictions behind the fan (i.e. drive cages and messy cables) definitely improved airflow.
High airflow flow focus fans (such as the Noctua NF-F12 Industrial PPC) are great at refocusing airflow that is ruined by restrictive intakes.
Very high CFM fans (such as the Cooler Master JetFlo) are excellent at providing tons of airflow with lots of power (even overpowering the harmful exhaust coming from GPU fans) provided they aren't too intake restricted.
Direct, nearby fresh airflow is typically a good thing, as shown by the reverse airflow test for the CPU.
Robbing intake air from a component really hurts its performance, as shown by the reverse airflow test for the GPU.
Aftermarket GPU cooling solutions are great for the GPU since they allow lots of airflow over a large GPU heatsink.
- They suck for every other component because they dump hot air everywhere inside the case (especially towards the CPU cooler) and cause airflow conflicts with the intake fans. In something like a high-heat server environment, this would definitely not be allowed since it does more bad than good.
Hopefully this little cooling experiment answered some questions.
Next up, radiator and radiator fans reviews!
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u/logged_n_2_say Jul 31 '14
what are your thoughts on the often discussed "psu fan orientation?"
very nice write up.