ISS Technology Update, Volume 7 Number 2 - Newsletter

ISS Technology Update Volume 7, Number 2
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As expected, the lower CFM exhaust air is hotter. But contrary to the belief that hotter exhaust air will result in higher server inlet
temperatures due to mixing, Computational Fluid Dynamics (CFD) modeling shows that the lower flow rate of the exhaust air
makes it less likely to be pulled to the front of the servers. CFD modeling also shows that the exhaust air mixes sufficiently before
reaching the Computer Room Air Conditioner (CRAC) coil, staying within CRAC inlet temperature limits. In fact, the reduction in
mixing at the inlet allows the CRAC inlet temperature to be set higher, which can result in significant power savings. These
savings can be realized by implementing sensor and control mechanisms such as HP Dynamic Smart Cooling, by statically
balancing the data center thermal solution, or by using CFD modeling.
Active Cool fans are controlled by the HP Onboard Administrator so that cooling capacity can be ramped up or down based
on the needs of the entire system. Similar to Active Cool Fans that operate at variable speeds, HP engineers developed another
power-saving technology, Dynamic Power Saver, which allows power supplies to run at higher load levels for greater
efficiency. It also turns off power supplies when they are not needed.
HP innovation didn’t stop there. Engineers developed the Parallel Redundant Scalable Enclosure Cooling (PARSEC), a new
BladeSystem enclosure design that enables the fans to be arrayed in a scalable, redundant manner, and ensures that all of the
air entering the enclosure is used for cooling.
HP innovation is ongoing. HP engineers and designers are currently investigating further opportunities to extend the energy
savings and minimize the environmental impact of data centers.
Additional resources
For additional information on the topics discussed in this article, visit the following URLs:
Resource URL
“Power and Cooling in the Data
Center”
www.sustainablefacility.com/CDA/Archives_EPM/BNP_GUI
D_9-5-2006_A_10000000000000024570
“HP BladeSystem c3000 Enclosure
technologies” technology brief
http://h20000.www2.hp.com/bc/docs/support/SupportMa
nual/c01204885/c01204885.pdf
“HP BladeSystem C7000 Enclosure
Technologies, 2nd Edition”
technology brief
http://h20000.www2.hp.com/bc/docs/support/SupportMa
nual/c00816246/c00816246.pdf.
Air ducting in HP BladeSystem enclosures
HP Thermal Logic technologies turn density into an advantage for cooling devices in HP BladeSystem c3000 and c7000
enclosures. In the c7000 enclosure, for example, six HP Active Cool fans need less than 100W to cool up to sixteen half-height
server blades with 25 percent less airflow than conventional fans. These unmatched efficiencies are enabled by the Parallel
Redundant Scalable Enclosure Cooling (PARSEC) architecture, which allows the fans to be arrayed so that all of the air entering
the enclosure is used for cooling. Ducting inside the enclosures delivers cool air from the front of the enclosure directly to each
device, allowing devices to stay cool with less airflow. This reduces fan power requirements, thus lowering operating cost and
the total cost of ownership of the devices and the facility.
Airflow through BladeSystem c3000 and c7000 enclosures is managed to ensure that every device gets cool air and that air
only goes where it is needed for cooling. For example, in the middle of the enclosures (Figure 3-1), all device bays include a
shutoff door that stays closed if a device is not installed (A). This prevents air leakage through empty device bays. When a
server blade is inserted (B), it seals into the center air plenum, and the server shut-off door opens to allow airflow across that
server blade. Similarly, each fan bay includes louvers (C) that automatically open when a fan is installed (D). If a fan is installed
but not working, the pressure distribution around that fan changes. This pressure change causes the non-operating fan’s louvers
to close, ensuring that cooling air is not lost through it.