Experimentally determining the coldest I can get with air
I’m trying to see how cool I can get my PC using air cooling. The best configuration so far has been replacing the stock heat sink with a Hyper 212 (taking off 26 C above ambient) and using a duct (taking off 7 degrees above ambient). I would appreciate other ideas for getting my system colder with air.
Intel Core i5-2500K
Stock heatsink/fan
SAPPHIRE Radeon HD 6950 2GB
G.SKILL Ripjaws Series 4GB DDR3 1600 9-9-9-24
Crucial RealSSD C300 64GB SATA III
ASRock P67 PRO3
COOLER MASTER HAF 912
XFX P1-650X-CAG9 650W ATX12V 2.2
Microsoft Windows 7 Home Premium 64-bit
Here are the changes I’ve made so far and what I’ve gotten from them. To measure the effect of a change, I ran LinX, Prime 95, and SuperPi for 10 minutes. During the last minute, I took the average temperature measured using the software that came with my motherboard (ASRock Extreme Tuning Utility). Ambient temperature was measured by a thermometer on the desk above my computer.
1) I replaced the stock heat-sink and fan with a Cooler master Hyper 212 Plus with Arctic Silver 5.
In both cases, I let the bios control the clock (it chose 3.3 Ghz) and the voltage (it chose 1.216 Vcore).
60 degrees C: stock heat-sink (ambient 18 degrees C)
49 degrees C: Hyper 212 & AR5 (ambient 15.6 degrees C)
The gap widened as I increased Vcore to 1.275V and clock to 4.7 Ghz.
80 degrees C: stock heat-sink (ambient 15.6 degrees C)
58 degrees C: Hyper 212 & AR5 (ambient 19.9 degrees C)
As an aside, one of the challenges I’ve been facing is maintaining a constant ambient temperature. In NJ, the weather has been really inconsistent and I’m too cheap to pay for heating. I’ve tried opening and closing my windows to various degrees, but it’s not very precise. Any ideas?
2) I experimented with various degrees of case enclosure.
In all cases, I set clock to 4.7 Ghz (47 * 100), voltage to 1.35 Vcore, short & long duration power limits to 500.
70 degrees C: default case (ambient 17.5 degrees C)
65 degrees C: open case—top, sides, and pci slot covers removed (ambient 17.5 degrees C)
72 degrees C: sealed case—I taped cardboard over all holes in the case without fans in them (ambient 18 degrees C)
In all cases, I set clock to 4.7 Ghz (47 * 100), voltage to 1.35 Vcore, short & long duration power limits to 500. The case fans are Coolermaster A12025-12CB-3BN-F1 fans (120 MM, 1200 RPM, 44 CFM, 19 dB). I managed to keep ambient at 18.9 degrees C for all of these trials.
65 degrees C: one fan low in the front and one fan high out the back (default HAF 912 configuration)
60 degrees C: one fan high out the back
65 degrees C: one fan high in the front and one fan out high in the back
66 degrees C: one fan high out the back and one fan out the top of the case
66 degrees C: one fan out the top
67 degrees C: one fan low in the front
67 degrees C: one fan in from the side
4) A co-worker suggested that I try a duct. His argument was that doing so would allow me to maximize the rate that air flowed past the heat-sink (and consequently convection).
65 degrees C: one fan low in the front and one fan high out the back (ambient was 18.9 degrees C)
67 degrees C: duct as pictured below (ambient was 17.8 degrees C)
I wasn’t thrilled with this result, but there were a couple of issues with this version of the duct.
-I couldn’t bend the duct from the heat-sink to the back of the case such that it lined up perfectly with the rear case fan hole (about half of the cross section is blocked). I’m thinking about taking a hole saw to the case, though would be open to a non-case damaging alternative.
-Also, the seals in the couplings that I machined weren’t perfect. I’m going to seal them with Loctite high temperature RTV.
-I’m not convinced that the ideal duct fan configuration is one on the heatsink and one in the rear. I’d like to try out a couple of different configurations to see what works best. If I had to guess, I would think based on my experience with fan configurations in the case that back only would be best.
5. I experimented with different heat-sink fans and heat-sink fan locations.
Experiment
All of these tests were done with a high back exhaust case fan and no duct. In all cases, I set clock to 4.7 Ghz (47 * 100), voltage to 1.35 Vcore, short & long duration power limits to 500.
The Stock 212+ fan does 75 CFM
The Rosewill RFA-120-BL does 75 CFM
The SILVERSTONE FM121 does 110 CFM
Results:
64 degrees C: Stock 212+ fan front intake (15.6 C ambient)
63 degrees C: Stock 212+ fan front intake & Rosewill RFA-120-BL fan back exhaust (15.6 C ambient)
62 degrees C: Rosewill RFA-120-BL fan back exhaust (15.6 C ambient)
62 degrees C: SILVERSTONE FM121 front intake and back exhaust (14.8 C ambient)
63 degrees C: SILVERSTONE FM121 back exhaust (14.8 C ambient)
62 degrees C: SILVERSTONE FM121 front intake (15.1 C ambient)
Implications
Surprisingly, it doesn’t seem that increasing the CFM of the fan has much of an impact. Less surprising was the fact that the higher CFM fans were louder (FM121’s generate 45 dB at desk level vs. 35 dB with Hyper212+ stock fan as measured by the Sound Meter app on my Droid 2)
The case for exhaust fan only in all situations is getting stronger. In the thread I linked before and in my case fan location experiment, I found that rear fan only produced the coldest temperatures. I’m seeing a similar thing here. Both the 75 and 110 CFM fans mounted on the rear of the heatsink, directed to exhaust produced the coldest or near coldest runs.
6. Controlling for ambient temperature
One problem I ran into was controlling for the ambient temperature. A suggestion I was given was to report CPU core temperature – ambient temperature instead of just CPU core temperature. For example, if CPU was 70 degrees C and ambient was 20 degrees C, I would report 50 degrees C. One concern I had was that I’m not sure that CPU temperature varies linearly with ambient temperature. Can anyone shed light on this?
Here are some highlights from previous experiments measured this new way.
49.2 C (67 C – 17.8 C): first duct attempt
47.5 C (65 C – 17.5 C): case front and sides removed
46.4 C (62 C – 15.6 C): Rosewill RFA-120-BL heat-sink rear exhaust, Coolermaster A12025 case rear exhaust.
45.6 C (67 C – 21.4 C): Coolermaster FA12025 heat-sink front intake, Coolermaster A12025 case rear exhaust.
7. Removing the rear fan grill
One suggestion I got was removing the rear fan grill (http://postimage.org/image/br30n09w). I removed it and replaced it with another fan guard that would let me keep my fingers but have less of an impact on air flow (http://postimage.org/image/br6bpp9g). I’ll take the 1 degree C cooler thank you very much.
45.6 C (67 C – 21.4 C): rear fan only with old grill
44.4 C (66 C – 21.6 C): rear fan only with new grill
46.3 C (65 C – 18.7 C): front and rear fan with old grill
45.4 C (67 C – 21.6 C): front and rear fan with new grill
8. Increasing negative pressure
I got some suggestions for increasing negative pressure. I tried them with the Coolermaster FA12025 front intake on the heat-sink and a Coolermaster A12025 rear exhaust on the case.
44.4 C (66 C – 21.6 C): Control
43.7 C (64 C – 20.3 C): Covering the top exhaust hole with two pieces of paper & Coolermaster A12025 case side exhaust
42.4 C (63 C – 20.6 C): Covering the top exhaust hole with two pieces of paper
These results are puzzling. As expected, covering the top cooled the CPU down (two degrees is a nice result). However, covering all the non-fan vents as I did in my varying case enclosure experiment proved disastrous (54 C = 72 C – 18C was the hottest above ambient I got in all my testing). The suggestion of adding a side fan to exhaust seemed natural given the success of having a rear exhaust fan only. But it happened to reduce cooling performance. The relationship between pressure and temperature in PC cooling is complicated. Any ideas for teasing it out?
9. Improving the duct
There were a couple of issues with the last version of the duct.
The rear exhaust fan was blocked. This was because the duct hose wasn’t flexible enough to get from the back of the heat-sink all the way to the exhaust hole. I replaced the duct with more flexible duct.
Not enough air was being drawn in. There was no front intake fan. I added one. The front of the duct was blocked by the 5 ¼” bay grill. I removed it (http://postimage.org/image/brhwh4pw/).
With those fixes, here’s what I got. Both measurements were taken with the front and rear grills removed.
44.9 C (66 C-21.1 C): Silverstone FM121 front intake & rear exhaust
38.2 C (59 C-20.8 C): Duct with Silverstone FM121 front intake & rear exhaust (http://postimage.org/image/br9mse90/)
11. Cooling the northbridge
One concern that was raised with the duct was that the north-bridge would run too hot. To remedy the issue, I tried putting a Rosewill RFA-120-BL on top of the case. Both trials increased the cpu – ambient so much that I decided against the top fan. All trials were done with the duct with Silverstone FM121 front intake & rear exhaust.
38.2 C (59 C-20.8 C): Control
41.2 C (62 C -21.8 C): Top fan set to exhaust
44.3 C (65 C -20.7 C): Top fan set to intake
Future actions
• I am going to pick up a vacuum and a pressure gauge to try to see what the deal is with pressure and temperature.
• I am going to buy some fans with the same CFM, but different static pressures and see how they perform.
• I will try adding some more space between the heat-sink and fan.
• I will try cooling the air before it enters the duct.
• I'll surround the front intake fan with foam for a better seal (thanks LedHed!)
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