![]() ![]() Comair Rotron urges engineers to minimize system impedance where practical, for best performance, noise, power and cost characteristics.Ĭombining fans in series of parallel can achieve the desired airflow without greatly increasing the system package size or fan diameter. Keeping in mind that a given fan can only deliver a single airflow into a given system impedance, the importance of system design on fan selection is critical. ![]() This would be considered a well-designed system from a forced convection cooling viewpoint. And if the system impedance could be optimized to where curve F were representative, then fan C would meet the airflow requirement, at a dramatically lower power, noise and cost level. If the system impedance could be improved to curve E, then fan B would meet the 50 CFM requirement, with a probable reduction in cost, noise and power draw. However, fan A is a high performance, higher noise fan that will likely draw more power and be more costly. If 50 CFM of air are needed, fan A will meet the need. Line D represents a system impedance within a given designed system. A is a 120 CFM fan, B is a 100 CFM fan and C is a 70CFM fan. To demonstrate the impact of system resistance on fan performance, figure 3 shows three typical fans used in the computer industry. Other considerations, such as available space and power, noise, reliability and operating environment should also be brought to bear on fan choice. Thus, before increasing the number of fans in a systems, or attempting to increase the air volume using a larger fan, the system should be analyzed for possible reduction in the overall resistance to airflow. The fan, in any given system, can only deliver as much air as the system will pass for a given pressure. The governing principle in fan selection is that any given fan can only deliver one flow at one pressure in a given system.įigure 2 shows a typical fan pressure versus flow curve along with what is considered the normal operating range of the fan. Once the volume of air and the static pressure of the system to be cooled are known, it is possible to specify a fan. Please contact Application Engineering for more information ![]() Comair Rotron makes this type of testing available. In any system, measurement of the static pressure will provide the most accurate result. Static pressure through complex systems cannot be easily arrived at by calculation.
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