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CPU cooling - exhuasting heat or bringing in ambiant?

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Last response: in Components
May 22, 2007 5:52:48 AM

Very new to building systems and confused with installation of the CPU heatsink/fan. I have the Zalman 9500 CPU fan with a Lian Li case. The Zalman instructions show the direction of the fan to be blowing or exhuasting out of the case. However, the case fan directly in-front of the CPU fan blows in to the case.

Obviously these fans should be blowing the same direction to maximize air flow across the fins/coils but, which way should it direct the air? bring ambiant air in to the case or exhaust out of the case?

Any / all suggestions would be appreciated - Thanks.

More about : cpu cooling exhuasting heat bringing ambiant

May 22, 2007 7:46:43 AM

The case is a LIAN LI PC-60BPLUSII W Black Aluminum ATX Mid Tower Computer Case. I am still working on the system in a bench top mode but noticed on their web site that the rear and front fan bring air in to the case and the top and side fans exhaust.

If I flip the case fan in the rear of the case to blow air out, there will be three fans exhausting (2-80mm and 1-120mm) with one bringing air in to the case (1-120mm). Do I need to balance the intake with the exhaust?

May 22, 2007 7:58:29 AM

Great idea - I will try both and monitor both CPU and system temps. to see which works best.

Thanks again for the help - greatly appreciated!!
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June 4, 2007 7:28:49 AM

OK, finally had time to test different fan configurations. A little background on the system;

Motherboard: MSI P6N Platinum
CPU: E6600
CPU Cooler: Zalman CNP9500
Case: Lian Li PC-60B Plus II
Video card: MSI NX8600-GTS-T2d256E-HD-OC (overclocked and runs hot ~50C)

The case has four fans;
Front fan: 120mm Scythe - SFF21E (slightly higher cfm than the "d" ver.)
Side fan: 120mm Scyth - SFF21D
Top fan: 80mm Enermax UC-8EB RTL
Rear fan: 80mm (same model as top fan)

Ambient air temperature at time of testing = 25.2
The temperatures reported in the following conditions are the approximate medians. All temperatures bounced around a little (~ +/- 2C)

Condition 1:
Front fan: intake
all other fans: exhaust (cpu fan air flow in same direction as rear fan)

Idle: Speedfan Core 0 29C, Core 1 30C
Idle: TAT Core 0 31C, Core 1 32C

Condition 2:
Front fan: intake
Rear fan: intake
all other fans exhaust (cpu fan air flow is now opposite of rear fan)

Idle: Speedfan Core 0 31C, Core 1 32C
Idle: TAT Core 0 33C, Core 1 33C

Condition 3:
Front fan: intake
Top fan: intake
all other fans exhaust (cpu fan air flow is back in same direction as rear fan)

Idle: Speedfan Core 0 28C, Core 1 29C
Idle: TAT Core 0 29C, Core 1 30C

100% Load on both cores (TAT)
Speedfan Core 0 57C, Core 1 58C
TAT Core 0 55C, Core 1 56C

The lowest and most stable temperatures (smallest range) was condition 3 with the Front and Top fans for air intake and the side and rear fans for exhaust.

A couple of notes - these are not the stock fans from the case. The fans used were purchased because of concerns with noise levels. I will say the case fans are virtually silent. I would recommend these fans fans for anyone looking to reduce noise levels. The CPU fan is NOT that quiet. It came with a variable speed controller and if the lowest setting is used (~1400 rpm), it is not bad but on the high setting (~2600 rpm) it is very audible. Strangely enough, there was absolutely no difference in Core temperatures between the high and low CPU fan settings.

Another oddity was the difference between Speedfan and TAT. In the Idle mode, Speedfan was consistently lower than TAT by about 2C. At the full load, Speedfan was consistently higher than TAT by about 2C. I have seen some references to calibrating Speedfan but I am still very new at this and have not taken the time to fully understand.

Many thanks to mpilchfamily for the response and help!! Hope this helps anyone else using the Lian Li case with a non-stock cpu fan.
June 4, 2007 7:58:45 AM

June 4, 2007 8:15:52 AM

This is true. I could have mounted the cpu fan so the air flow would blow up in to the p/s fan. Just lazy on my part, didn't want to pull the m/b to remount the cpu fan.