ASHRAE Journal - January 2013 - 61

Data Centers

Data Center energy Metric
I
By Donald L. Beaty, P.e., Fellow ASHRAE

Power Usage Effectiveness (PUE)

n November’s column, “Data Centers: Cooling as a Service,” we reviewed why data centers often use “Cooling as a Service” (CaaS) model, whereby

energy-efficiency scenarios were explored to examine their impact. It was stated in the report that these strategies could potentially reduce electricity use by up to 55%.

the cooling systems or “service” must be provided in a fashion that can scale effectively and efficiently with the IT services it supports. Using this model helps drive energy-efficiency improvements and more effective use of capital. In this month’s column, we’re going to introduce metrics or key performance indicators developed by the data center industry, which have furthered the cause of energy efficiency, from design through operations.
The data center industry has typically been dominated by a focus on reliability/ uptime and capital cost. A simple metric (not perfect, but effective) called power usage effectiveness (PUE) was created by The Green Grid (www.thegreengrid.org) that really impacted the data center industry’s focus on energy. It is important for anyone involved in data centers to have a good understanding of PUE including its integration with design and operation. This article provides some insight into data center requirements prior to the genesis of PUE, formation of the metric, and subsequent PUE developments and refinements. mental systems, etc.). Failures or outages to critical business operations would be sufficient to get people fired, whereas, no one ever got fired for the energy costs. Naturally, this made reliability/uptime a primary driver in the design of data centers. Since this driver invariably involved a more resilient and reliable system that had multiple redundant components as fail-safes, the capital cost associated with the data center was also a major driver. The balance between reliability/uptime and capital cost depended on the company and industry. As mentioned in November’s column, Colo Data Center energy costs are metered and subsequently a pass-through cost to the tenant. At about the same time energy cost increases were getting more focus, the capital cost of volume servers were going down. This translated into energy costs getting an increasing interest as they represented a larger percentage of the total lease contract costs and a substantially greater proportion of a server’s life-cycle costs. By projecting energy consumption trends five years into the future, several

the Green Grid & PUe
Prior to 2007, for the most part the energy efficiency of a data center was strictly an afterthought behind the mission critical mindset of reliability, availability, redundancy and uptime. With a global movement towards energy efficiency in many industries throughout the world coupled with the ever increasing power densities and overall consumption of data centers, the energy efficiency became more and more pronounced. Seeing the lack of a formal methodology for measuring data center energy efficiency, The Green Grid (a non-profit, open industry consortium of end-users, policy makers, technology providers, facility architects, and utility companies) introduced the calculation of a new energy efficiency metric called power usage effectiveness (PUE) that went on to become the widely accepted industry de facto standard. The premise behind PUE was to identify how much of the total power consumption of a data center was actually being used to run the IT equipment (servers, etc.). Therefore, PUE was simply defined as the ratio of Total Facility Power/IT Equipment Power to expose how much “overhead” power was used by the data center for elements such as the power needed to cool the IT equipment and for inefficiencies in the power distribution chain.

Pre-PUe Data Center Drivers
The data center industry is sometimes referred to as the mission critical industry, and some data centers are called mission critical facilities. This stems from some data centers being developed for “missions” that were “critical” since their failure would result in the failure of critical business operations (e.g., emergency response and telecommunication systems, financials, transportation control, governJanuary 2013

establishing PUe Consistency
Although the simplicity of the PUE metric was a catalyst to its rapid acceptance in the data center industry, it also led to a lot of gaming of the metric.
ASHRAE Journal 61



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
ASHRAE Journal - January 2013 - 39
ASHRAE Journal - January 2013 - 40
ASHRAE Journal - January 2013 - 41
ASHRAE Journal - January 2013 - 42
ASHRAE Journal - January 2013 - 43
ASHRAE Journal - January 2013 - 44
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
ASHRAE Journal - January 2013 - 54
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ASHRAE Journal - January 2013 - 56
ASHRAE Journal - January 2013 - 57
ASHRAE Journal - January 2013 - 58
ASHRAE Journal - January 2013 - 59
ASHRAE Journal - January 2013 - 60
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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