Ashrae Journal - November 2008 - (Page 18)

ing gaps in floors, using blanking panels in open spaces in racks, and avoiding mixing of hot and cold air. ASHRAE has published several excellent publications on these best practices, including Datacom Equipment Po wer Trends and Cooling Applications. Computational fluid dynamics (CFD) can be used to identify inefficiencies and optimize data center airflow. Many organizations offer CFD imaging as part of data center assessment services focused on improving cooling efficiency. Additionally, temperatures in the cold aisle may be able to be raised if current Figure 2: Power supply efἀciency can vary signiἀcantly depending on load, and power suptemperatures are below 68°F (20°C). plies are often sized for a load that exceeds the maximum server conἀguration. Chilled water temperatures can often be raised from 45°F to 50°F (7°C to 10°C). In the data center model, cooling system efficiency is improved 5% simply by implementing best practices. This reduces overall facility energy costs by 1% with virtually no investment in new technology. 7. 415V ac power distribution. The critical power system represents another opportunity to reduce energy consump- Figure 3: 415V power distribution provides a more efἀcient alternative to using 208V power. tion. However, even more than with other systems, care must be taken to ensure reductions in energy These systems may compromise equipment protection because consumption are not achieved at the cost of reduced equipment they do not fully condition incoming power. availability. A bigger opportunity exists downstream from the UPS. In Most data centers use a type of UPS called a double-con- most data centers, the UPS provides power at 480V, which is version system. These systems convert incoming power to dc then stepped down via a transformer, with accompanying losses, and then back to ac within the UPS. This enables the UPS to to 208V in the power distribution system. These stepdown losses generate a clean, consistent waveform for IT equipment and can be eliminated by converting UPS output power to 415V. effectively isolates IT equipment from the power source. UPS The 415V three-phase input provides 240V single-phase, systems that don’t convert the incoming power—line interactive line-to-neutral input directly to the server (Figure 3). This higher or passive standby systems—can operate at higher efficiencies voltage eliminates stepdown losses and enables an increase in because of the losses associated with the conversion process. server power supply efficiency. In the model, an incremental 2% reduction in facility energy use is achieved by using 415V ac power distribution. 8. Variable capacity cooling . Data center systems are sized to handle peak loads, which rarely exist. Operating efficiency at full load is often not a good indication of actual operating efficiency. Newer technologies, such as digital scroll compressors and variable frequency drives in computer room air conditioners (CRACs), allow high efficiencies to be maintained at partial loads. Digital scroll compressors allow the capacity of room air conditioners to be matched exactly to room conditions www.info.hotims.com/16019-50 18 ASHRAE Journal November 2008 http://www.wrightsoft.com http://www.wrightsoft.com http://www.info.hotims.com/16019-50

Table of Contents Feed for the Digital Edition of Ashrae Journal - November 2008

Ashrae Journal - November 2008 Contents Commentary Industry News Meetings and Shows Feature Articles Reducing Data Center Energy Consumption Building Sciences Feature Articles Sustainable Nature Center Emerging Technologies Special Products Washington Report Special Supplement: BACnet® Today BACnet® Goes Green Seeing the Light with BACnet® BACnet® on Campus BACnet® for Net Zero Analyzing BACnet® BACnet® at Xerox Campus BACnet® in Europe BACnet® for Green Library BACnet® at the University of Minnesota: Flexibility, Interoperability InfoCenter Product Showplace Classified Advertising Advertising Index

Ashrae Journal - November 2008

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