HP BladeSystem c-Class architecture Technology brief, 4th edition

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Active Cool fans
Some small form-factor servers such as blade or 1U servers use very small fans to provide localized
cooling in specific areas. Because these fans generate low airflow (measured in cubic feet per minute,
or CFM) at medium backpressure, a single server often needs multiple fans to cool it.
Blower-style fans provide cooling across an entire enclosure. These fans are good at generating high
airflow, but have the following drawbacks:
• They usually need more power.
• They produce more noise.
• They do not adjust for load. They run to cool for the highest load in an enclosure, constantly
generating high airflow.
An alternative to the very small fan and blower-style fan is the HP Active Coolfan. The Active Cool fan
delivers high airflow and high pressure in a small form factor. It uses ducted fan technology with a
high-performance motor and impeller to deliver high CFM at high pressure. Use the Active Cool 100
fan in a c3000 enclosure and the Active Cool 200a fan in a c7000 enclosure.
The Onboard Administrator controls the thermal logic algorithms of the Active Cool fans. Onboard
Administrator ramps up or lowers the cooling capacity based on the needs of the entire system. Along
with optimizing airflow, the fan’s control algorithm optimizes acoustic levels and power consumption.
Even as new fans become operational, the Onboard Administrator thermal logic algorithms remain
unchanged. Microprocessors inside the Active Cool fans translate the thermal logic algorithms into the
actual rotor speeds required for the fan.
Active Cool fans deliver better performance than other fans in the server industry because of their
mechanical design and the control algorithm. By aggregating the cooling capabilities of a few high-
performance fans, we reduced the overhead of having many, localized fans for each server blade.
This simplifies cooling and lowers the cost of the entire architecture.
Mechanical design to optimize airflow
By design, each c-Class enclosure lets fresh, cool air flow over all the server blades (in the front of the
enclosure) and all the interconnect modules (in the back of the enclosure). HP optimizes the cooling
capacity across the enclosure by optimizing airflow and minimizing leakage using a central plenum,
self-sealing louvers surrounding the fans, and automatic shut-off doors surrounding the device bays.
A dedicated side slot in the front of the enclosure pulls fresh air into the interconnect bays. Ducts move
the air from the enclosure’s front to the rear, where the air is then pulled into the interconnect modules
and the central plenum, and then exhausted from the rear of the system.
Each power supply module has its own fans, optimized for the airflow characteristics of the specific
power supplies. The exhaust air does not interfere with the airflow path of the server blades or
interconnect modules, because the power supplies are in a separate part of the enclosure.
Because the enclosures have separate cooling zones, the Active Cool fans cool their own zone and
provide redundant cooling for the rest of the enclosure. One or more fans can fail and still leave
enough fans to cool the enclosure adequately. The number of fans that can fail depends upon the
number of blades, the number of fans, and the location of the blades. The Onboard Administrator
reports thermal subsystem status and redundancy level, and it updates the system log and alert HP
SIM when the thermal subsystem status changes.
Enclosure Dynamic Power Capping
With Enclosure Dynamic Power Capping, you can set a power cap for an entire BladeSystem
enclosure, including all the individual server blades. When you use this capability, the Onboard