Thermally Advantaged Small Chassis (TASC) Design Guide

Section 2
10 E60781
2.1.1.2 Side Vent Description
Location and size
The Design Guide requires a side vent as seen in Figure 3. The vent directly over the
CPU fan heat sink is most critical for CPU cooling. The location also allows the CPU fan
to draw cool air in most effectively and thereby helps with overall internal cooling.
This vent configuration has been optimized by means of extensive system level
testing. The size of this vent is recommended to be 130mm wide and 100mm tall. The
side vent is best located with respect to a subset of the standard ATX mounting holes
as defined in the ATX Specification. Refer to Section 5 for detailed vent size and
location dimensions.
Figure 3. Side Vent Illustration
Free Area Ratio
Free area ratio (FAR) is defined as the total vent open area, divided by the vent area.
It is recommended that this vent have an effective open area of at least 53%. This will
maximize the effectiveness of the vent and should still contain EMI effectively. Higher
FAR’s will improve airflow into the chassis but are at the expense of aesthetics, safety,
and increased EMI emissions. Lower open area percentages will degrade thermal
performance but may still be effective depending on the entire system design. These
are design choices the chassis designer must understand and make appropriate
compromises for the performance
The chassis designer may want to provide features on the chassis side panel to
mitigate vent blocking if the system should be placed against a wall, desk or other
obstruction.