Electrical Efficiency Modeling for Data Centers

Elect rical Efficiency
Mode ling for Data
Cent ers


By Neil Rasmussen
White Paper #113
Revision 1



Executive Summary
Conventional models for estimating electrical efficiency of data centers are grossly
inaccurate for real-world installations. Estimates of electrical losses are typically made by
summing the inefficiencies of various electrical devices, such as power and cooling
equipment. This paper shows that the values commonly used for estimating equipment
inefficiency are quite inaccurate. A simple, more accurate efficiency model is described
that provides a rational basis to identify and quantify waste in power and cooling
equipment.
©2006-2007 American Power Conversion. All rights reserved. No part of this publication may be used, reproduced, photocopied, transmitted, or stored in any retrieval system of any nature, without the written permission of the copyright owner. www.apc.com WP113 - 0 2Introduction
The 10-year total cost of ownership (TCO) for network-critical physical infrastructure (NCPI) in a typical data center can be $80,000 to $150,000 per rack. Of this cost, the cost of electrical power consumption is a 1significant contributor, on the order of 20% of the total cost . This is of interest because much of the electrical power consumption is wasted (in the form of heat energy) and a significant amount of this waste is avoidable. It is estimated that, world-wide, data centers consume 40,000,000,000 kW-hr of electricity per year and the reduction of waste associated with this consumption is a significant public policy issue as well ~~as a major financial concern to data ~~2center operators. Typical simplistic models of data center efficiency grossly underestimate electrical waste in data centers. The entitlement to improved efficiency is consequently much greater than commonly believed. This paper presents an improved model that provides better accuracy for data center losses and suggests where energy improvement opportunities are available.
What is "Data Center Efficiency"?
The efficiency of any device or system is the fraction of its input (electricity, fuel, whatever makes it "go") that is converted to the desired useful result - anything other than the useful result is considered to be "waste." This fraction of useful out to total in is usually expressed as a percent. "Useful" is whatever is considered the desired result for the particular system, which may depend not only on the nature of the system, but also on the context of its use. For example, a light bulb whose output consists of 5% light and 95% heat can be viewed as a 5% efficient light bulb or a 95% efficient heater, depending upon whether it is being used to light a room or heat a room. "Useful output" is whatever makes sense for the system under consideration. For data center physical infrastructure, the input is electricity and the useful output is power for the computing equipment. In this paper, a data center is modeled as an electrical system whose "total input" is
1 Details on the contributors to TCO are described in APC White Paper #6, Determining Total Cost of Ownership for Data Center and Network Room Infrastructure 2 http://www.eei.org/magazine/editorial_content/nonav_stories/2004-01-01-NT.htm (accessed June 14, 2006).
©2006-2007 American Power Conversion. All rights reserved. No part of this publication may be used, reproduced, photocopied, transmitted, or stored in any retrieval system of any nature, without the written permission of the copyright owner. www.apc.com WP113 - 0 3the power it consumes from the utility and whose "useful output" is the amount of power for computing it 3provides, which can be represented by the amount of electrical power delivered to the IT equipment. IT load power Data center efficiency = Total data center input power Figure 2 illustrates this general model of data center efficiency. Figure 2 - Data center efficiency is defined as the fraction of input power delivered to the IT load Power delivered to the IT load is a measure of useful output for the data center DDaattaa cceenntteerr DDaa... [download for more]