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Efficient Fans Drive Cost-Effective Thermal Management in Enclosures and Cabinets
Smart control fan.

Electronic enclosures and cabinet systems continue to pack more power into smaller volumes, resulting in higher thermal loads per cubic foot. Thermal management for such systems can be challenging, requiring smaller and more efficient air-moving devices to disperse heat. AC or DC fans and fan trays are typically the solutions for thermal management in these systems. Properly controlled temperatures in an enclosure or cabinet system can mean the difference between optimum performance and reliability problems, especially in industrial automation, control systems, and data-communications/telecommunications applications.

While thermal management is vital for optimal performance of electronic equipment, conserving energy as part of achieving high overall electronic efficiency is also an important design consideration. Fan manufacturers are improving the efficiency of their components through the use of various intelligent control and feedback options, as well as by meeting high-performance specifications.

Smaller Fans, Bigger Airflows
As electronic equipment density (and the heat the equipment generates) increases in cabinets and enclosures, cooling solutions must evolve to meet the meet the increasing thermal-management demands of those electronic systems. Cooling challenges are being presented by electronic systems that are being miniaturized but still produce large amounts of heat. Semiconductor packages, power supplies, and printed-circuit boards (PCBs) are being made smaller, with increasing amounts of heat being generated per unit volume.

Many engineers attempting to address thermal management in a cabinet or enclosure system rely on the basic principle that heat rises. This may not properly disperse the heat in a densely packed electronic equipment cabinet or enclosure due to the cumulative effects of heat generated within that cabinet or enclosure. Electronic hardware that is mounted at higher levels of the cabinet or enclosure will endure higher temperatures that ventilation alone may not solve. Compounding the problem is the fact that in many enclosures the heat source does not radiate in an even distribution pattern.

Heat sources within a cabinet or enclosure can be anything from motors, power supplies, PCBs, lighting, and other components, and can create hot spots within the cabinet or enclosure. Conventional thermal management approaches may not properly deal with these hot spots, leaving hot spots that can be threats to electronic equipment in terms of degrading performance and causing failures.

Finding Hot Spots
Because these hot spots are not always discovered in the design process, engineering redesigns are often required, leading to longer lead times for components, creating scheduling issues and, thus, potentially resulting in loss of market share for that final product. To address thermal management issues stemming from the greater heat per volume of more miniaturized electronic components, fan manufacturers are designing fans with higher airflow (in cubic foot per minute or CFM) in smaller fan case sizes.
Short fan tray fits in standard 19-inch rack.

Specifying fans that provide high CFM airflow in a small case size is one option for design engineers wrestling with the thermal management of a cabinet or enclosure system. Designers need to provide overall temperature control of an electronic system, but also the capability to manage airflow at specific locations within the system, to prevent hot spots from developing. For example, if fan trays are mounted at the top of an enclosure, they might deliver a combined airflow of 2100 CFM, which is usually enough to maintain the given enclosure at a proper temperature. However, this solution may not address a particular hot spot inside the enclosure caused by an especially compact, heat-emitting piece of equipment.

Directed Airflow
Dissipating heat from a particular hot spot within an electronic equipment cabinet or enclosure can be accomplished by directing airflow at the source of the heat, using sufficient airflow to move the heat out of the cabinet or enclosure. For this purpose, directional blowers can be used, since these low-profile devices provide directional cooling similar to spot coolers but in flat, compact designs. Directional blowers are often used even in larger applications, such as server rooms. Rather than blasting air out of the back of an electronic system, air is directed in smaller amounts, in more controlled directions. This approach helps meet the space and directional requirements of many different applications, since directional blowers can also provide the speed and airflow necessary to optimize thermal management.

In addition to moving more air using higher fan CFM ratings, fan manufacturers are also providing improved performance levels within fan trays. As a function of ambient air temperature, each fan within a fan tray may be equipped to adjust its speed between 55 percent and 100 percent of full speed, which helps maximize fan operating life, saves energy, and minimizes fan noise. Fan and fan tray expansion modules also allow customers to add or subtract fan modules quickly and easily as cooling needs change.

Boosting Functionality, Conserving Energy
Manufacturers of cabinets and enclosures continually face demands for reduced energy consumption and limited space — in addition to the challenge of managing the internal heat generated by the system. Fan manufacturers solve these problems by employing special functions in their fan designs, such as tachometer outputs, locked rotor alarms, pulse width modulation (PWM) inputs, as well as thermal and constant speed controls.

A tachometer output provides design engineers with an accurate means of monitoring and reporting a fan's rotational speed, as well as indicating if the fan speed falls below a specified revolutions per minute (RPM) operating speed. Typically, the tachometer output option is available as either a 5V TTL signal, or as an "open collector" signal.

Fans and fan trays equipped with locked-rotor alarms indicate whether a fan has stopped operating by transmitting a high or low output signal, thus avoiding a potential overheating situation. A PWM input varies the width of the electrical pulse in order to control the average voltage delivered to a fan, for increased efficiency compared to a linear control approach. A PWM option also allows users to digitally control the speed of the fan through an existing bus system or programmable logic controller (PLC).

These special functions or "smart controls" not only provide intelligent control options and feedback that increase fan functionality and optimize fan performance, but they also maximize energy conservation by allowing manufacturers the capability to better monitor airflow and operating temperature, ensuring the fans are operating properly and at optimal conditions. This is particularly true with thermal and constant speed controls.

Fans and fan trays with thermal speed controls employ a thermistor-controlled circuit that increases fan speed only when the temperature rises above a determined set point. This "green" option reduces overall energy consumption by lowering fan speed when temperatures within the enclosure are below the set point, providing cooling (and consuming energy) only as needed. In server farms, for example, a thermistor-controlled fan will only turn on (or speed up) above a critical, programmed temperature, conserving energy and extending fan operating lifetimes by running fans only as needed.

Thermistor control circuits can be mounted directly in the fan hub or remotely mounted via a lead wire, and can be positioned anywhere, giving design engineers the flexibility to regulate fan speed based on ambient temperature in a specific area. In addition, a constant speed function senses variable input voltage, which can cause variations in power output (and thus fan speed and airflow), and compensates to maintain the fan's constant speed regardless of input voltage fluctuations.

Fans are important system components, particularly in densely packed electronic enclosures and cabinets where equipment performance and reliability depends upon minimizing excess generated heat. Stabilizing the temperature within an enclosure or cabinet allows the electronics to operate at maximum capacity and optimum performance levels. In addressing thermal management, specialty fans with design ingenuity and "smart controls" help OEMs and end customers minimize thermal problems caused by densely packed electronic designs.

Through the use of these intelligent control and feedback options, as well as enhanced performance specifications (including higher CFM ratings), end users are provided with greater functionality while meeting "green" requirements. In short, fans make sense for any application in which movement of a large amount of air can help achieve superior thermal management and reliable, long-term equipment performance.

Contact: Knight Electronics, Inc., 10557 Metric Dr., Dallas, TX 75243 800-323-2439, 214-340-0265 fax: 214-340-5870 Web:

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