Active Cool Fans - HP BladeSystem c3000 Technology Brief

Active Cool fans

Quite often, dense, full-featured, small form-factor servers use very small fans designed to provide
localized cooling in the specific areas needed by the server blade. Because such fans generate fairly
low airflow (in cubic feet per minute, or CFM) at medium backpressure, a single server often requires
multiple fans to ensure adequate cooling. Therefore, installing many server blades together in an
enclosure, with each server blade containing several fans, can result in significant cost and space
overhead.
A second solution for cooling is to use larger, blower-style fans that can provide cooling across an
entire enclosure. Such fans are good at generating CFM, but they typically require higher power
input, take up more space, make more noise, and must be designed for the maximum load in an
enclosure. As a result, designers may have to sacrifice server features to allow the large, high-power
fans to fit in the enclosure. Even then, ensuring adequate airflow to all the servers without leakage,
over provisioning, or bypass is a challenge.
To overcome these issues for the HP BladeSystem c-Class, HP engineers designed a new type of fan
based on aircraft technology that delivers both high airflow and high pressure in a small form factor
that can scale to meet future cooling needs. HP Active Cool fan technology optimizes airflow, reduces
power draw, and improves acoustic performance for any server blade configuration.
With 20 patents pending involving Active Cool fan technology and its implementation, HP Active
Cool fans are an innovative design that can cool eight server blades using as little as 100 watts of
power. Active Cool fans use ducted fan technology (the fan is longer than it is wide) with a high
performance motor and impeller (Figure 3) to deliver high CFM at a high pressure. The fan includes a
bell mouth inlet with a specially-designed impeller, followed by a stator section that also provides
cooling fins for the motor and acoustic treatments in the rear of the fan. This design providies cooling
capacity to support blade products beyond current roadmaps. Its unique shape allows for high-
pressure flow at even the slowest speeds with low noise levels and minimal power consumption.
Figure 3. Ducted fan cross-section and ducted fan blade compared to traditional server fan
Active Cool fans are controlled by the c-Class Onboard Administrator so that cooling capacity can be
ramped up or down based on the needs of the entire system. Along with optimizing the airflow, this
control algorithm allows the BladeSystem c-Class to optimize the acoustic levels and power
consumption. As a result, the c3000 Enclosure requires less airflow (CFM) than traditional rack-mount
servers to properly cool the server blades within the enclosure.
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