The Advantages of Row and Rack- Oriented Cooling Architectures for Data Centers
ABSTRACT
Room cooling is an ineffective approach for next-generation data centers. Latest generation high density and variable density IT equipment create conditions that room cooling was never intended to address, resulting in cooling systems that are inefficient, unpredictable, and low in power density. Row-oriented and rack-oriented cooling architectures have been developed to address these problems. This paper contrasts room, row, and rack architectures and shows why row-oriented cooling will emerge as the preferred solution for most next generation data centers.
FULL DOCUMENT
The Advantages of Row and Rack-Oriented Cooling Architectures for Data Centers
White Paper #130
By Kevin Dunlap
Neil Rasmussen
2006 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. http://www.apc.com Rev 2006-0 2
Introduction
All of the electrical power delivered to the IT loads in a data center ends up as waste heat that must be removed to prevent over temperature conditions. Virtually all IT equipment is air-cooled, that is, each piece of IT equipment takes in ambient air and ejects waste heat into its exhaust air. Since a data center may contain thousands of IT devices, the result is that there are thousands of hot airflow paths within the data center that together represent the total waste heat output of the data center; waste heat that must be removed. The purpose of the air conditioning system for the data center is to efficiently capture this complex flow of waste heat and eject it from the room. Room-based cooling is the historical method for accomplishing data center cooling. In this approach, one or more air conditioning systems, working in parallel, push cool air into the data center while drawing out warmer ambient air. The basic principle of this approach is that the air conditioners not only provide raw cooling capacity, but they also serve as a large mixer, constantly stirring and mixing the air in the room to bring it to a homogeneous average temperature, preventing hot-spots from occurring. This approach is effective only as long as the power needed to mix the air is a small fraction of the total data center power consumption. Simulation data and experience show that this system is effective when the average power density in data is on the order of 1-2 kW per rack, translating to 323-753 W/m2 (30-70 W/ft2). Unfortunately, the power densities of modern IT equipment are pushing peak power density to 20 kW per rack or more, where simulation data and experience show that room-based cooling dependent on air mixing no longer functions effectively.
To address this problem, new design approaches are emerging that focus on row or rack based cooling. In these approaches the air conditioning systems are specifically integrated with rows of racks or individual racks. This provides much better predictability, higher density, higher efficiency, and a number of other benefits. In this paper, the various approaches are explained and contrasted. It will be shown that each of the three approaches has an appropriate application, and in general a trend away from room based cooling toward row based cooling should be expected for higher density applications.
