Energy Efficient Cooling for Data Centers: A Close-Coupled Row Solution

Energy Efficient Cooling
for Data Centers: A
Close-Coupled Row
Solution
By John Bean, Member ASHRAE Kevin Dunlap
From an article published in ASHRAE Journal, October 2008
White Paper #137
Executive Summary
The trend of increasing heat densities in data centers has held consistent with advances in
computing technology for many years. As power density increased, it became evident that
the degree of difficulty in cooling these higher power demand loads was also increasing. In
recent years, traditional cooling system design has proven inadequate to remove
concentrated heat loads (up to and greater than 20 kW per rack). This has driven an
architectural shift in data center cooling. The advent of a newer cooling architecture that
was designed for the higher densities has brought with it increased efficiencies for the data
center. This article discusses the efficiency benefits of row-based cooling compared to two
other common cooling architectures.

©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 WP137 Rev 0 2The following article was published in ASHRAE Journal, October 2008. ©Copyright 2008 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. It is presented for educational purposes only. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE.
Energy-Efficient
Data Centers
A Close-Coupled Row Solution
By John Bean, Member ASHRAE; and Kevin Dunlap from IT equipment without mixing with supply air. This separation results in hot ?he predominant architecture for cooling data centers since the inception of spots and a complicated design approach the mainframe has been raised floor air delivery from perimeter computer to air distribution. T To add to this problem, the airflow room air handlers (CRAH). In this approach, CRAHs are placed around the demands of the IT equipment also increases with power density. Since perimeter of the room, and they distribute cold air through a raised floor with CRAH and CAHU systems use a plenum for supply air delivery (and perforated floor tiles or vents to direct the air into the room (Figure 1). At lower warm air return in certain designs), a significant amount of fan horsepower densities (1 to 5 kW/rack) adequate cooling is provided to sensitive IT equip- is required to pressurize the plenum and overcome resistances in the air-ment, despite the mixing of air throughout the room. distribution system. Additionally, to overcome the effects of mixing the net A similar air delivery system that has As rack power grew beyond 5 kW, air volume of air circulated is significantly been used to cool data centers is central delivery and heat removal challenges greater than actual air volume required air-handling units (CAHU) (Figure 2). with use of CRAH and CAHU systems These systems use much larger, more became evident. The major obstacle in About the Authorscentralized cooling units with similar air these architectures is the length scale of John Bean is director of innovation for racks and delivery to perimeter CRAH cooling of air delivery. Distance between the cooling cooling and Kevin Dunlap is general manager for either raised floor or custom overhead units and the heat load make it difficult cooling solutions at American Power Conversion ductwork. to properly remove the heat generated in O'Fallon, Mo.
34 ASHRAE Jo u rna l a s h r a e . o r g O c t o b e r 2 0 0 8While row-based designs addressed the issue of proper heat removal and cold air
supply, they also brought with them inherent energy-efficiency advantages. The first
of these was a reduction in fan power requirement to move the air.
by IT equipment further compounding energy consumed supply temperature (no need to overcool the air to com-by fans. pensate for mixing).To address the air delivery and heat removal challenges of .. Limited or no condensate removal, reducing mak... [download for more]