Using Improved High Density Power Distribution to Increase Data Center Efficiency

Incre asing Data
Center Efficiency by
Using Improved High
Dens ity Power
Distribution
By Neil Rasmussen
White Paper #128
Revision 1



Executive Summary
A new approach to power distribution for high density server installations saves floor
space, simplifies power cabling, saves capital cost, reduces weight, and increases electrical
efficiency. This paper describes this distribution architecture and quantifies the benefits.

Note: The methods in this paper only apply in North America and are for problems that are
unique to North America




©2006-2008 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 WP128 Rev 1 2Introduction
The standard power distribution system for large data centers in North America is a 277/480V three-phase power system supplying distributed Power Distribution Units (PDUs) which convert the voltage to the 208V and 120V single-phase branch circuits utilized by IT equipment. This arrangement is represented by the one-line diagram of Figure 1. Figure 1 - One-line diagram showing standard power distribution system for North American data centers PDU(s)
120 / 208 V
120 / 208 V
277 / 480 V 277 / 480 VUPS
120 / 208 V
High density server installations where racks can draw from 10 kW to 40 kW per rack place significant strains on this standard power distribution system. This increased rack power density is causing: . Multiple branch circuits per rack, with corresponding breakers and cabling . PDUs to become up to 30% of the floor space . PDUs to become up to 30% of the floor weight loading . More PDUs installed per IT rack, driving up capital costs However, these problems are unique to North America. In Europe and the rest of the world the power distribution system is simpler and more efficient. This paper shows that it is practical to take the power distribution system used in the rest of the world and apply it to North American data centers to reduce cost, reduce weight, save floor space, and increase electrical efficiency.
©2006-2008 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 WP128 Rev 1 3 In the past it was not practical to consider alternative higher voltage power distribution systems because a significant fraction of IT equipment operated from 120V. However in the modern high density data center virtually all rack-based equipment operates on 208V (or 240V outside North America). Even devices that can run on 120V are also capable of operating on higher voltage. Virtually all IT equipment manufactured today is designed for worldwide compatibility. This means it can operate on the North American 120/208 volt system, the Japanese 100/200 volt system, and the 240 V system used in the rest of the world.
Alternative Power Distribution for North America
The alternate power distribution system proposed and described in this paper is an adaptation of the power distribution system used in the rest of the world. The majority of countries around the world use 230 VAC line to neutral. This paper proposes increasing the voltage to 240 VAC line to neutral since this is the highest voltage supported by most IT equipment. This arrangement is represented by the one-line diagram of Figure 2. Figure 2 - One-line diagram showing alternative power distribution system for North American data centers 240 /4 15
240 /4 15
277/ 480 277/480 240/415UPS 240 /4 15
Autotransformer 240 /4 15
240 /4 15
The differences between this diagram and the diagram of Figure 1 are subtle, and include: . Three-phase branch circuit power distribution that is 240 V (line to neutral) instead of 208 V (line to line) . Elimination of the PDU transformers . A transformer that is used to change 277/480 V to 240/415 V at the output of the UPS.
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