Thermally Advantaged Small Chassis (TASC) Design Guide

Section 2
8 E60781
2.1.1.1 System Fans
System Exhaust Fan:
It is necessary that heat generated within the chassis be effectively exhausted and
therefore requires the use of an exhaust fan. It is the responsibility of chassis
manufacturer to ensure the performance of the exhaust fan and ensure that an
appropriate balance of performance and acoustics is met. While the location of the
exhaust fan may be dependent on the chassis design, there are a few considerations
that should be made in determining its location.
 Fan placement should be as free from obstruction as possible to minimize flow
impedance and provide sufficient exhausting airflow. It is particularly
important to provide means of cable management that does not interfere with
or block fan inlets and exhausts.
 It may be desirable to put the fan in line critical components to provide
airflow.
 If the addition of an add-in card would obstruct the system fan, it would not
be recommended to put the exhaust fan on the West wall of the chassis (Side
nearest PCI slots).
 If chassis is designed to accommodate a mini tower configuration, a fan
exhaust should not be blocked by either the floor or chassis stand.
 Generally, the East side of chassis is most convenient and effective for
exhaust fan placement as shown in Figure 2.
With the above considerations, the most generic location seems to be the East side of
the chassis in line with the DIMM slots.
Note: Some enclosure designs may utilize system pressurizing via intake fans for
thermal management. This is a design choice that is not intended or recommended in
this Design Guide.
Power Supply Exhaust Fan
There are several options available for type of power supply to be used in small form
factor systems. No changes or special considerations beyond air flow direction are
intended for power supplies in this design guide.
Use of a standard desktop power supply such as Flex ATX, or TFX type may be
beneficial for cost, availability, and established reliability. In addition, it may be the
case that a standard desktop power supply has sufficient exhaust capability to
relinquish the need of a system fan, but this must be carefully verified by the designer
and is not without risk depending on system layout and components.
When a standard desktop power supply is used, it should be ensured that it is placed
so that it exhausts outside of the chassis. A power supply fan that only circulates air
within the chassis will not be a good design choice. Likewise, a chassis power supply
fan that pressurizes the chassis would render the vent location and size recommended
by this guide ineffective.
The use of external power supply is an obvious way to reduce system size. In this
case, a properly sized system fan is especially important as the primary exhaust