ASHRAE Journal - December 2010 - 44

power usage effectiveness (PUE). The support power (energy) ratio is defined as the ratio of the power required to support the operation of the (ICT) equipment in the data center to the power required by the ICT equipment. It is easy to measure; we obtained the support power by subtracting the UPS power output from the total incoming power to the data center. PUE is equal to one plus the support power ratio. The existing data center’s support power ratio was measured at 0.75 (or a PUE of 1.75) before its expansion. Incidentally, several studies from ASHRAE, Uptime Institute, DOE’s Lawrence Berkeley National Laboratory5 and the U.S. EPA point to an average PUE of 2.0, or a support energy ratio of 1.0. Therefore, the existing data center with a support power ratio of just 0.75 was more efficient than the industry practices. The expansion in this project added 60% more ICT capacity. However, with heat containment, use of variable airflow, supply air temperature control (as opposed to conventional return air temperature control) and other enhancements to chiller operations for energy efficiency, the overall support power ratio is now measured at 0.41 (or a PUE of 1.41). The annual facility total energy consumption from May 16, 2008 to May 15, 2009 was 90.5 million kWh (utility billing data), and the ICT equipment energy use was 61 million kWh (measured from the UPS output), providing a support energy ratio of just 0.41 for the combined old and new data center expansion. If we were to have the same design for the expansion section as for the existing data center with a support energy ratio of 0.75 (or PUE of 1.75), our facility energy use for supporting a 61 million kWh ICT energy use would have been 107 million kWh instead of the measured 90.5 million kWh. The energy-efficient design and operation provided a savings of 16.2 million kWh in fiscal year 2008–09. These data have been collected and processed using the U.S. EPA ENERGY STAR Data Center program measurement, data collection, and reporting protocol. The data have been recently submitted to the ENERGY STAR as a program participant (see “ENERGY STAR for Data Centers”).
Indoor Air Quality

AC Rack

Figure 1: Hot spots and hot air recirculation with conventional air distribution. from the ICT equipment is ducted directly to plenum for return to the CRAC units and does not impact human comfort. The air is dehumidified by the ventilation air unit to an acceptable dew-point temperature in the data center space before it is delivered to the data center. This eliminates any dehumidification requirement on the data center CRAC units. It also enhances overall operating energy efficiency since data center CRAC units do not have to remove moisture and can operate with warmer chilled water.
Innovation

Ventilation air is preconditioned and delivered by an independent constant speed air-handling unit. The unit is sized for the designed occupancy and meets the requirements of ASHRAE Standard 62.1. In addition, the data center operating conditions are well within ASHRAE Standard 55 parameters. The hot air

Conventional air distribution causes hot air to recalculate to ICT equipment (Figure 1). A computational fluid dynamics
center qualifies for the ENERGY STAR label. EPA recently developed the ENERGY STAR model with data provided by several organizations. This project data was submitted for the model development initiative. Although Oracle has not formally requested the ENERGY STAR rating for this data center, this project qualifies for the ENERGY STAR rating. For more information, visit www.energystar.gov/ datacenters.

ENERGY STAR for Data Centers
Beginning this year, stand-alone data centers and buildings that house large data centers can earn the ENERGY STAR label. To earn the label, data centers must be in the top 25% of their peers in energy efficiency according to EPA’s energy performance scale. EPA uses power usage effectiveness to determine if a data

ASHRAE Journal

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December 2010

ASHRAE Journal - December 2010

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