Monday, May 21, 2018
Publication Date: 07/1/2008
Archive >  July 2008 Issue >  Tech Watch > 
Thermal Simulation Speeds Smaller, Quieter PCs to Market

BTX (Balanced Technology eXtended) is a new personal computer form factor that improves the cooling of critical components, making it possible to reduce noise levels and the size of the case. Design of systems based on the new form factor can present challenges from a thermal standpoint since the new designs have only two fans, compared to three to five fans.

In order to assist systems builders, particularly smaller manufacturers without a large engineering staff, a series of reference designs were developed to serve as a starting point for the mechanical design of different types of BTX systems. Developing these designs using the traditional build and test approach would taken a long time and been expensive because of the need to build and test many prototypes. Instead Intel used Flotherm software from Flomerics Inc. to evaluate a large number of potential designs from a thermal and acoustic standpoint and used the diagnostic information from the simulation to iterate quickly to an optimized design prior to the prototyping phase.

BTX Thermal Improvements
BTX thermal improvements come primarily from taking advantage of in-line airflow. The defined in-line airflow layout allows many of the main board components — processor, chipset, and graphics controller — to utilize the same primary fan airflow, thereby reducing the need for, and noise from, additional system fans. In some cases this also allows fewer or less expensive heat sinks to be used when compared to ATX solutions. The system level acoustics are also improved by the reduced air turbulence within the in-line airflow system. The BTX layout supports better component placement for back panel I/O controllers which is important as the signal speed of external devices continues to increase. BTX provides for sizes smaller than the smallest possible with the ATX form factor and is designed to scale up to tower size systems using the same core layout by increasing the number of system slots included. A key change in the BTX form factor is that instead of the fan in the processor heat sink blowing air down onto the processor it blows air sideways across the processor. From there the airflow is directed through ducts and used to cool other components. A critical part of developing the new form factor was proving that it would provide the desired reductions in noise and case size while keeping all of the components inside the case cool. Engineers performed an extensive series of computer simulations to in order to evaluate the performance of a series of designs based on the new standard and to provide guidelines to companies developing designs.

Entertainment PC
The BTX entertainment PC was designed to be stacked with other audio-visual equipment and optimized to meet stringent acoustic targets. The industrial design more closely resembles a consumer electronics device than a typical personal computer. This reference design is particularly interesting because traditional ATX designs have never been able to meet the requirements of this application. The greatest design challenge is meeting the tough acoustic requirements of the application.

BTX is a system architecture that is well suited for fan speed reduction, making it possible to reduce fan speed through a substantial reduction in air temperature and airflow impedance. But the entertainment reference design needed to have an attractive front bezel that is unencumbered by ventilation openings. The basic principle used in this design was to place use side, bottom, and top panel ventilations near the thermal module inlet in order to minimize inlet impedance that would otherwise make it necessary to increase thermal module fan speed. Engineers also placed higher power components in the primary airflow stream generated by the thermal module.

Safe Temperatures
Of course, as the engineers developed this initial concept design they were uncertain as to whether it would maintain component temperatures at safe levels. They didn't have the time or resources to build the large number of prototypes that would have been required to validate the initial concept using trial and error methods. But they did have Flotherm thermal simulation software. They developed an initial mechanical layout, modeled the design in Flotherm, and viewed the results. The temperature profiles through the chassis showed hot spots in the dual line memory modules (DIMMs). The airflow speed and direction profiles, on the other hand, showed that the hard drives restricted airflow moving out of the back of the case.

Engineers took advantage of the ability of thermal simulation to determine the impact of design changes quickly. They added a vent over the memory to reduce inlet impedance in this area and evaluated different geometrical patterns for this and other vents in which the openings ranged from 20 percent to 80 percent from both a thermal and an acoustic standpoint. They evaluated acoustics by estimating acoustic signatures with hand calculations. Using this approach they were able to reduce thermal impedance to the point where they were finally able to cool the DIMMs.

Most BTX reference designs position the power supply on the left side of the case but this is not a requirement of the form factor. The engineers had the idea that it would provide better airflow on the right side. They made the change and viewed the results and discovered that this hunch was correct. However, at this point the noise generated by the system was at 3.6 Bels (BA) sound power with the thermal module fan running at idle speed.

The thermal simulation experiments evaluated the design at a number of different fan speeds, starting at the level of 1800 rpm and reducing the speed until components began to overheat. In this case fan speed was reduced to 650 rpm, which made it possible to hit the acoustic target. While the fan originally didn't run at 650 rpm, engineers spoke to the manufacturer and convinced them to change the control system so it could run at this speed.

The resulting reference design — along with other reference designs that were developed — is being used by systems builders to reduce the time required for design of BTX systems. The systems builders almost never use the reference design exactly as-is, but it helps them a lot to begin with a validated design with known thermal and acoustic characteristics. In order to further simplify the design process for its customers a series of thermal simulation templates for BTX designs were developed. Users of Flotherm software can select these reference designs from a library and make any modifications they wish to provide added value to their customers. Flotherm currently includes four BTX designs, a micro tower, a slim tower, and desktops with one and two thermal modules, as well as nine ATX reference designs. Additional reference designs will be added in the near future.

Contact: Flomerics Inc., 4 Mount Royal Ave., Suite 450, Marlborough, MA 01752 508-357-2012 fax: 508-357-2013 E-mail: Web:

search login