ASHRAE Journal - January 2013 - 62

Data Centers
Through taking advantage of the lack of Year Maximum Scenario specificity for the measurement criteria, Achievable 2007 2008 2009 2010 2011 claims of artificially low PUE hampered the Current ability for the metric to be believable and 2.0 1.98 1.95 1.93 1.9 – Trends led to a subsequent expansion of the PUE metric in 2009 by the Green Grid to create Improved 1.94 1.88 1.82 1.76 1.7 1.7 Operation more consistent and comparable metrics. Best The criteria addressed by the expansion: 1.9 1.8 1.7 1.6 1.5 1.3 Practices • System (physical) location of the meaState of surement of the IT equipment power and 1.89 1.78 1.67 1.56 1.45 1.2 the Art the total facility power; report1 statement of baseline PUE of 2.0 in 2006 and a • Frequency of the measurements of the The data in this table is based on the EPA and 2011. The valuesafor the alternate scenarios were thenlinear improvement in infrastructure efficiency between 2007 extrapolated from IT equipment power; and the trends graph in the EPA report that indicated annual electricity use savings. • Duration considered for the averaging Table 1: EPA predictions for data center PUE ratios. of the data collected. This expansion led to a complex suffix system with a number power efficiency alone by considering the total CO2 emissions of variables accounted for. The complexity led to a consortium per unit of IT equipment energy. of industry groups, including ASHRAE and the Green Grid • Water Usage Effectiveness (WUE): with water becoming themselves, to issue a clarification white paper that simplified a key resource in data center cooling systems, this metric was the suffix system and to address elements such as data centers developed to quantify the annual water consumption per unit in a mixed use building. of IT equipment energy. The white paper defined four categories for measuring PUE within a data center, each increasing the level of accuracy for Integration of PUE into Data Center Design & Operation the measurement. It has become commonplace for PUE to be quoted as an attri• PUE Category 0 (PUE0): a demand-based calculation mea- bute of a given data center. It has helped define everything from sured during peak IT equipment utilization over a 12 month how “green” a data center design is to actually being a baseline period (a simple snapshot). for calculating rental payments for data center colocation space. • PUE Category 1 (PUE1): a consumption based calculation As its awareness and influence has grown on the industry, using a cumulative measurement over a 12-month period at the more and more data centers are being designed through a focus output of the Uninterruptible Power Supply (UPS) supporting on lowering PUEs. Predominantly, this has resulted in designs the IT equipment loads. that seek to minimize the amount of energy that is consumed • PUE Category 2 (PUE2): a consumption based calculation by the cooling system which has traditionally been the biggest using a cumulative measurement over a 12-month period at the contributor to non-IT equipment power loads in a data center. output of the Power Distribution Unit (PDU) supporting the IT In some cases, this has led to a reduction in capacity or an equipment loads. outright elimination of compressor based mechanical refrigera• PUE Category 3 (PUE3): a consumption based calculation tion through a combination of design techniques and operational using a cumulative measurement over a 12-month period at the protocols such as operating at a higher temperature overall, point of connection of the IT equipment. having better airflow management (less mixing of airstreams), which leads to an increase in economizer (free cooling) hours.

Expanding the PUE Metric Family

Building upon the broad industry acceptance of PUE, the Green Grid has developed additional metrics to further standardize the quantification of data center energy efficiency results. The following is a brief overview of some of those metrics: • Compute Power Efficiency (CPE): a metric that seeks to define how efficiently of the power delivered to the IT equipment is converted into a useful work product. • Data Center Energy Productivity (DCeP): a metric to track the overall useful work product of a data center per unit of total data center energy consumed to produce this work. • Energy Reuse Effectiveness (ERE): a metric that tracks and effectively credits the overall energy efficiency of a data center if waste energy from the data center is reused. • Carbon Usage Effectiveness (CUE): a metric that helps with defining the overall sustainability of a data center beyond the
62 ASHRAE Journal

Conclusion
Although reliability/uptime and capital cost remain important considerations in data center design and operation, energy efficiency has also become an equally important consideration. The de-facto acceptance of PUE as a measurement of infrastructure energy efficiency in data centers is also significantly influencing their design and operation as well as shaping the expectations amongst data center owners and operators.

References
1. EPA. 2007. “Report to Congress on Server and Data Center Energy Efficiency: Public Law 109-431.” http://tinyurl.com/2jz3ft.

Donald L. Beaty, P is president of DLB Associates Consult.E., ing Engineers, in Eatontown, N.J. He is publications chair of ASHRAE TC 9.9.
ashrae.org January 2013



ASHRAE Journal - January 2013

Table of Contents for the Digital Edition of ASHRAE Journal - January 2013

ASHRAE Journal - January 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Long-Term Commercial GSHP Performance: Part 6: Maintenance and Controls
Thermally Active Floors, Part 1
Technology Award Case Studies:
Aquathermal Systems
Standing Columns
Data Centers
People
Emerging Technologies
IAQ Applications
Engineer's Notebook
Washington Report
Refrigeration Applications
Classified Advertising
Advertisers Index
ASHRAE Journal - January 2013 - ASHRAE Journal - January 2013
ASHRAE Journal - January 2013 - Cover2
ASHRAE Journal - January 2013 - 1
ASHRAE Journal - January 2013 - 2
ASHRAE Journal - January 2013 - Contents
ASHRAE Journal - January 2013 - Commentary
ASHRAE Journal - January 2013 - 5
ASHRAE Journal - January 2013 - Industry News
ASHRAE Journal - January 2013 - 7
ASHRAE Journal - January 2013 - 8
ASHRAE Journal - January 2013 - 9
ASHRAE Journal - January 2013 - 10
ASHRAE Journal - January 2013 - 11
ASHRAE Journal - January 2013 - 12
ASHRAE Journal - January 2013 - 13
ASHRAE Journal - January 2013 - 14
ASHRAE Journal - January 2013 - 15
ASHRAE Journal - January 2013 - Letters
ASHRAE Journal - January 2013 - 17
ASHRAE Journal - January 2013 - Meetings and Shows
ASHRAE Journal - January 2013 - 19
ASHRAE Journal - January 2013 - 20
ASHRAE Journal - January 2013 - 21
ASHRAE Journal - January 2013 - 22
ASHRAE Journal - January 2013 - 23
ASHRAE Journal - January 2013 - Long-Term Commercial GSHP Performance: Part 6: Maintenance and Controls
ASHRAE Journal - January 2013 - 25
ASHRAE Journal - January 2013 - 26
ASHRAE Journal - January 2013 - 27
ASHRAE Journal - January 2013 - 28
ASHRAE Journal - January 2013 - 29
ASHRAE Journal - January 2013 - 30
ASHRAE Journal - January 2013 - 31
ASHRAE Journal - January 2013 - Thermally Active Floors, Part 1
ASHRAE Journal - January 2013 - 33
ASHRAE Journal - January 2013 - 34
ASHRAE Journal - January 2013 - 35
ASHRAE Journal - January 2013 - 36
ASHRAE Journal - January 2013 - 37
ASHRAE Journal - January 2013 - 38
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ASHRAE Journal - January 2013 - 40
ASHRAE Journal - January 2013 - 41
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ASHRAE Journal - January 2013 - 45
ASHRAE Journal - January 2013 - 46
ASHRAE Journal - January 2013 - 47
ASHRAE Journal - January 2013 - Aquathermal Systems
ASHRAE Journal - January 2013 - 49
ASHRAE Journal - January 2013 - 50
ASHRAE Journal - January 2013 - 51
ASHRAE Journal - January 2013 - 52
ASHRAE Journal - January 2013 - 53
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ASHRAE Journal - January 2013 - Data Centers
ASHRAE Journal - January 2013 - 62
ASHRAE Journal - January 2013 - 63
ASHRAE Journal - January 2013 - People
ASHRAE Journal - January 2013 - Emerging Technologies
ASHRAE Journal - January 2013 - 66
ASHRAE Journal - January 2013 - 67
ASHRAE Journal - January 2013 - IAQ Applications
ASHRAE Journal - January 2013 - 69
ASHRAE Journal - January 2013 - 70
ASHRAE Journal - January 2013 - 71
ASHRAE Journal - January 2013 - Engineer's Notebook
ASHRAE Journal - January 2013 - 73
ASHRAE Journal - January 2013 - 74
ASHRAE Journal - January 2013 - 75
ASHRAE Journal - January 2013 - Washington Report
ASHRAE Journal - January 2013 - Refrigeration Applications
ASHRAE Journal - January 2013 - Classified Advertising
ASHRAE Journal - January 2013 - Advertisers Index
ASHRAE Journal - January 2013 - 80
ASHRAE Journal - January 2013 - Cover3
ASHRAE Journal - January 2013 - Cover4
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