DOCSLIB.ORG

Liquid Cooling Guidelines for Datacom Equipment Centers

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Liquid Cooling Guidelines for Datacom Equipment Centers | Second Edition Centers Equipment Liquid Cooling Guidelines for Datacom The Guide Every Datacom Professional Needs Liquid Cooling Data center rack heat loads are steadily climbing, and the ability for many data centers to deliver either adequate airflow rates or chilled air is now being stretched to the limit to avoid decreased equipment availability, wasted floor space, and inefficient cooling system operation. This situation is creating a Guidelines need for liquid cooling solutions to reduce the volume of airflow needed by the racks and for lower processor temperatures for better computer perfor- mance. This book provides cooling system designers, data center operators, equipment manufacturers, chief information officers (CIOs), and IT specialists for Datacom with best practice guidance for implementing liquid cooling systems in data centers. This second edition includes updated references and further information Equipment Centers on approach temperatures and liquid immersion cooling, plus guidance on water quality problems and wetted material requirements. It also includes definitions for liquid and air cooling as they apply to the IT equipment, along with an overview of chilled-water and condenser water systems and other datacom equipment cooling options. The book also bridges the liquid cooling systems by providing guidelines on interface requirements between the chilled-water system and the technology cooling system and on the Second Edition requirements of liquid-cooled systems that attach to a datacom electronics rack to aid in data center thermal management. This book is the fourth in the ASHRAE Datacom Series, authored by ASHRAE Technical Committee 9.9, Mission Critical Facilities, Data Centers, Technology Spaces and Electronic Equipment. This series provides com- prehensive treatment of datacom cooling and related subjects. ISBN 978-1-936504-67-1 ASHRAE Datacom Series, Book 4 4 ASHRAE Datacom Series 9 781936 50467 1 1791 Tullie Circle, NE 4 Atlanta, GA 30329-2305 Product code: 90564 3/14 www.ashrae.org/bookstore LiquidCoolingCover_2ndEd_tb.indd 1 2/6/2014 3:01:27 PM © 2014 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission. Liquid Cooling Guidelines for Datacom Equipment Centers Second Edition © 2014 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission. Liquid Cooling Guidelines for Datacom Equipment Centers is authored byASHRAE Tech- nical Committee (TC) 9.9, Mission Critical Facilities, Data Centers, Technology Spaces, and Electronic Equipment.ASHRAE TC 9.9 is composed of a wide range of industry repre- sentatives, including but not limited to equipment manufacturers, consulting engineers, data center operators, academia, testing laboratories, and government officials who are all committed to increasing and sharing the body of knowledge related to data centers. Liquid Cooling Guidelines for Datacom Equipment Centers is not anASHRAE Guideline and has not been developed in accordance with ASHRAE’s consensus process. For more information on the ASHRAE Datacom Series, visit www.ashrae.org/datacenterefficiency. For more information on ASHRAE TC 9.9, visit http://tc99.ashraetcs.org/ Any updates/errata to this publication will be posted on the ASHRAE Web site at www.ashrae.org/publicationupdates. © 2014 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission. Liquid Cooling Guidelines for DatacomEquipment Centers Second Edition ASHRAE Datacom Series Book 4 Atlanta © 2014 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission. ISBN 978-1-936504-67-1 © 2006 and 2014 ASHRAE 1791 Tullie Circle, NE Atlanta, GA 30329 www.ashrae.org All rights reserved. Printed in the United States of America Cover image by Joe Lombardo of DLB Associates. ASHRAE is a registered trademark in the U.S. Patent and Trademark Office, owned by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. ASHRAE has compiled this publication with care, but ASHRAE has not investigated, and ASHRAE expressly disclaims any duty to investigate, any product, service, process, procedure, design, or the like that may be described herein. The appearance of any technical data or editorial material in this publi- cation does not constitute endorsement, warranty, or guaranty by ASHRAE of any product, service, process, procedure, design, or the like. ASHRAE does not warrant that the information in the publica- tion is free of errors, and ASHRAE does not necessarily agree with any statement or opinion in this publication. The entire risk of the use of any information in this publication is assumed by the user. No part of this publication may be reproduced without permission in writing from ASHRAE, except by a reviewer who may quote brief passages or reproduce illustrations in a review with appropriate credit, nor may any part of this publication be reproduced, stored in a retrieval system, or transmitted in any way or by any means—electronic, photocopying, recording, or other—without permission in writing from ASHRAE. Requests for permission should be submitted at www.ashrae.org/permissions. Library of Congress Cataloging-in-Publication Data Liquid cooling guidelines for datacom equipment centers. -- Second edition. pages cm -- (Datacom series ; 4) Includes bibliographical references and index. Summary: "Provides information on liquid cooling for datacom equipment centers. Concerned with energy efficiency"-- Provided by publisher. ISBN 978-1-936504-67-1 (softcover) 1. Data processing service centers--Cooling. 2. Electronic data processing departments--Equipment and supplies-- Protection. 3. Hydronics. 4. Electronic apparatus and appliances--Cooling. 5. Electronic digital computers-- Cooling. 6. Buildings--Environmental engineering. I. American Society of Heating, Refrigerating and Air- Conditioning Engineers. TH7688.C64L57 2014 697.9'316--dc23 2014000819 ASHRAE STAFF SPECIAL PUBLICATIONS Mark S. Owen, Editor/Group Manager of Handbook and Special Publications Cindy Sheffield Michaels, Managing Editor James Madison Walker, Associate Editor Roberta Hirschbuehler, Assistant Editor Sarah Boyle, Assistant Editor Michshell Phillips, Editorial Coordinator PUBLISHING SERVICES David Soltis, Group Manager of Publishing Services and Electronic Communications Jayne Jackson, Publication Traffic Administrator Tracy Becker, Graphics Specialist PUBLISHER W. Stephen Comstock © 2014 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission. Contents Acknowledgments.........................................vii Chapter 1 Introduction .....................................1 1.1 Definitions ........................................3 1.2 Liquid Cooling Systems.............................5 Chapter 2 Facility Cooling Systems ..........................9 2.1 Introduction.......................................9 2.2 Equipment .......................................14 Chapter 3 Facility Piping Design ............................25 3.1 General .........................................25 3.2 Spatial Considerations.............................26 3.3 Basic Piping Architecture ..........................27 3.4 Piping Arrangements for the Cooling Plant ............36 3.5 Water Treatment Issues ............................39 3.6 Seismic Protection ................................39 Chapter 4 Liquid Cooling Implementation for Datacom Equipment.............................41 4.1 Overview of Liquid-Cooled Racks and Cabinets ........41 4.2 Overview of Air- and Liquid-Cooled Datacom Equipment 46 4.3 Overview of Immersion Cooling of Datacom Equipment . 50 4.4 Overview of Coolant Distribution Unit (CDU)...........52 © 2014 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission. vi Contents Chapter 5 Liquid Cooling Infrastructure Requirements for Facility Water Systems ........................59 5.1 Facility Water Systems (FWS)........................59 5.2 Non-Water Facility Systems .........................80 5.3 Liquid Cooling Deployments in NEBS Compliant Space. .82 Chapter 6 Liquid Cooling Infrastructure Requirements for Technology Cooling Systems ...................87 6.1 Water-Based Technology Cooling System .............87 6.2 Non-Water-Based Technology Cooling System .........92 References and Bibliography ................................93 Glossary of Terms .........................................95 Appendix ................................................101 Index ...................................................103 © 2014 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission. Acknowledgments Representatives from the following companies participated in
Recommended publications
  • Green Field Data Center Design – Water Cooling for Maximum Efficiency

    Green Field Data Center Design – Water Cooling for Maximum Efficiency

    GREEN FIELD DATA CENTER DESIGN – WATER COOLING FOR MAXIMUM EFFICIENCY Shlomo Novotny, Vice President and Chief Technology Officer, Vette Corp. Overview Data centers are an ever‐growing part of our economy. The IT community is experiencing constantly increasing demands in areas such as Internet media and video, banking and finance, research, and government, just to name a few. Consequently, data centers continue to grow in both size and numbers. In addition, the performance of IT servers continues to follow Moore’s law; this improves the performance per dollar spent on IT equipment, but also increases the heat density inside the data center equipment. Driven by these factors, the cost of running a data center continues to grow, even as the cost of the IT performance continues to decline. Historically, data center management has been focused on growth, performance, uptime, and reliability. IT organizations generally had responsibility for data center management. Facility organizations were responsible for much of the infrastructure surrounding the IT equipment. As a result of the significant growth and the lack of a holistic view of the economics of data centers, data center facilities today can be compared to factories of the 1970s and 1980s: ripe for significant cost, design, and process improvements. With attention from C‐level executives today, data centers are driven to be lean, scalable, cost effective, and green. One of the most inefficient issues with many data centers today revolves around cooling. Typically, data center operators have managed heat density issues by spreading the load and under populating racks. This has come about because of the limitations of air cooling, which creates a very costly, complex, and inefficient infrastructure.
  • Liquid in the Rack: Liquid Cooling Your Data Center

    Liquid in the Rack: Liquid Cooling Your Data Center

    AUGUST 21- 23, 2018 • CLEVELAND, OHIO Liquid in the Rack: Liquid Cooling Your Data Center Dale Sartor, PE Norman Bourassa awrence Berkeley Lawrence Berkeley National Laboratory National Laboratory Otto Van Geet, PE National Renewable Energy Laboratory Contact Information Dale Sartor, P.E. Lawrence Berkeley National Laboratory MS 90-3111 University of California Berkeley, CA 94720 [email protected] (510) 486-5988 http://datacenters.lbl.gov/ Agenda • Introduction to Liquid Cooling • Case studies • Interactive Discussion Liquid Cooling Solution Typical liquid cooled equipment room, with external coolant distribution units (CDUs) For most locations these data centers may be operated without chillers in a water-side economizer mode Benefits of Liquid Cooling • Higher compute densities • Higher efficiency • Heat removal • Transport energy • cooling plant • Increased economizer hours • Potential use of waste heat Moving (Back) to Liquid Cooling . As heat densities rise, liquid solutions become more attractive . Volumetric heat capacity comparison (5,380 m3) (1.5 m3) ~ 190,000 cubic foot blimp = Water Air Why Liquid Cooling? . Higher compute densities . Liquids can provide cooling at higher temperatures • Improved cooling efficiency • Increased economizer hours • Potential use of waste heat . Reduced transport energy: In-Row Liquid Cooling Graphics courtesy of Rittal In-Rack Liquid Cooling Racks with integral coils and full containment: Cooling Coil Rear-Door Heat Exchanger . Passive technology: relies on server fans for airflow . Active technology: supplements server fans with external fans in door . Can use chilled or higher temperature water for cooling Photo courtesy of Vette Liquid On-Board Cooling . Clustered Systems design . Conducting heat to a cold plate containing refrigerant Liquid On-Board Cooling .
  • Guide to Minimizing Compress-Based Cooling

    Guide to Minimizing Compress-Based Cooling

    Guide to Minimizing Compressor-based Cooling in Data Centers Prepared for the U.S. Department of Energy Federal Energy Management Program By: Lawrence Berkeley National Laboratory Author: William Tschudi May 2013 Contacts William Tschudi Lawrence Berkeley National Laboratory One Cyclotron Road, 90R3111 Berkeley, California 94720 510-495-2417 [email protected] For more information on FEMP, please contact: Will Lintner, P.E. Federal Energy Management Program U.S. Department of Energy 1000 Independence Ave. S.W. Washington, D. C. 20585-0121 202.586.3120 [email protected] Cover photo: Center for Disease Control and Prevention's Arlen Specter Headquarters and Operations Center reached LEED Silver rating through sustainable design and operations that decrease energy consumption by 20% and water consumption by 36% beyond standard codes. Photo from Center for Disease Control, NREL/PIX 16419 2 Acknowledgements The author would like to thank Romonet for their assistance in conducting the technical simulations utilized in this guide. 3 Table of Contents 1 Introduction ........................................................................................................................................... 5 2 The opportunity .................................................................................................................................... 6 3 Steps for minimizing or eliminating compressor-based cooling .................................................... 7 3.1 Adopt indoor environmental conditions that promote efficiency
  • Edge and Data Center Cooling Solutions Precision and High Density Liquid Cooling

    Edge and Data Center Cooling Solutions Precision and High Density Liquid Cooling

    Edge and Data Center Cooling Solutions Precision and High Density Liquid Cooling CADDY ERICO HOFFMAN RAYCHEM SCHROFF TRACER nVent.com/DNS | 1 Edge And Data Center Cooling Solutions Introduction Increasing heat densities challenge Content streaming, online banking, cloud computing, sophisticated smart phone apps, eCommerce, industrial data center operators and the automation. These are just a few examples of applications that are fueling data processing and traffic demand in data demand for reduced data latency centers throughout the world. Emerging technologies, such requires more computing power at as Artificial Intelligence (AI), telemedicine, machine learning, autonomous (driverless) vehicles and other real time modeling the edge. applications will accelerate demand further. CABLE MANAGEMENT PRECISION PROFESSIONAL COOLING SERVICES CABLE SUPPORT AND PATHWAYS MONITORING FASTENING AND FIXING ELECTRICAL PROTECTION CONTAINMENT NETWORKING RACKS HIGH DENSITY LIQUID COOLING LEAK DETECTION RACK POWER SERVER CABINETS Find out more on nVent Cooling Solutions 2 | nVent.com/DNS Precision And Liquid Cooling Overview Data Center Cooling Solutions Edge Computing Cooling Solutions Maintaining high availability (uptime) at minimal operational The rapid emergence of Big Data, 5G, Industry 4.0 and IoT costs remains a major challenge in today’s data centers and deployments also require protection for edge-computing networks. A significant portion of budgets includes energy applications, such as high-speed wireless, autonomous consumption for IT equipment and server cooling. vehicles, industrial automation, transportation, security and nVent offers a comprehensive range of standard and safety systems. These complex systems are powered by customized air, indirect and direct water cooling solutions. smaller and faster electronics that require effective cooling Our product range enables you to meet these challenges and protection to ensure maximum operating performance and protect your IT assets, whether for smaller decentralized edge uptime.
  • The Facility Perspective on Liquid Cooling

    The Facility Perspective on Liquid Cooling

    Dale Sartor The Facility Perspective on Lawrence Berkeley National Laboratory Liquid Cooling: Experiences and Anna Maria Bailey Proposed Open Specification Lawrence Livermore National Laboratory David Grant SC18 Birds of a Feather Oak Ridge National Laboratory Herbert Huber November 13, 2018 Leibniz Supercomputing Centre, LRZ Dave Martinez Version: 11/08/18 Sandia National Laboratory 1 | Federal Energy Management Program femp.energy.gov Agenda • Overview of warm water liquid cooling • Introductory remarks from panelists (strategies and lessons learned) • Overview of open specifications for liquid cooled rack • Panel and audience discussion 2 Warm Liquid Cooling - Overview Dale Sartor, P.E. Lawrence Berkeley National Laboratory SC18 Birds of a Feather November 13, 2018 Version: 11/05/18 3 | Federal Energy Management Program femp.energy.gov Liquid Cooling Solution Typical liquid cooled equipment room, with external coolant distribution units (CDUs) For most locations these data centers may be operated without chillers in a water-side economizer mode 4 Benefits of Liquid Cooling • Higher compute densities • Higher efficiency Vision: Eliminate compressor based cooling and water consumption 5 Moving (Back) to Liquid Cooling • As heat densities rise, liquid solutions become more attractive • Volumetric heat capacity comparison (5,380 m3) (1.5 m3) ~ 190,000 cubic foot blimp = Water Air 6 Why Liquid Cooling? • Liquids can provide cooling at higher temperatures – Improved cooling efficiency – Increased economizer hours – Potential use of waste
  • Failure Analysis of Direct Liquid Cooling System in Data Centers

    Failure Analysis of Direct Liquid Cooling System in Data Centers

    Proceedings of the ASME 2017 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems InterPACK2017 August 29-September 1, 2017, San Francisco, California, USA IPACK2017-74174 FAILURE ANALYSIS OF DIRECT LIQUID COOLING SYSTEM IN DATA CENTERS Sami Alkharabsheh, Bharath Ramakrishnan, Bahgat Sammakia Department of Mechanical Engineering Binghamton University Binghamton, NY, USA ABSTRACT RU rack unit In this paper, the impact of direct liquid cooling (DLC) SNMP simple network management protocol system failure on the IT equipment is studied experimentally. SPT set point temperature The main factors that are anticipated to affect the IT equipment T temperature (°C) response during failure are the CPU utilization, coolant set point U CPU utilization temperature (SPT) and the server type. These factors are varied experimentally and the IT equipment response is studied in terms INTRODUCTION of chip temperature and power, CPU utilization and total server Cooling was reported to consume 30%-40% of the total power. It was found that failure of the cooling system is energy used in legacy data centers [1]. Despite the optimistic hazardous and can lead to data center shutdown in less than a data center energy consumption trends in a recent survey [2], the minute. Additionally, the CPU frequency throttling mechanism average power usage effectiveness (PUE) was reported to be 1.8 was found to be vital to understand the change in chip mostly due to inefficiencies in the cooling system [3]. Several temperature, power, and utilization. Other mechanisms thermal management technologies are used in data centers associated with high temperatures were also observed such as the cooling to address the inefficiency challenges [4].
  • Fujitsu Cool-Central Liquid Cooling Technology

    Fujitsu Cool-Central Liquid Cooling Technology

    ISC15 Frankfurt July 2015 Fujitsu Cool-Central® Liquid Cooling Technology Fujitsu Cool-Central® Liquid Cooling Technology Efficient cooling of large PRIMERGY CX400 M1 HPC or cluster solutions Fujitsu Cool-Central® Liquid Cooling Technology helps to reduce data center cooling costs by over 50 % and allows for 2.5-5x higher data center server density. 1 © 2015 Fujitsu Why On-Chip Liquid Cooling? Maximum rack Less cooling Lower investment Lower overall density power and needed for energy costs building new data consumption centers Extreme dense Liquid cooling A hot water based Hot water based liquid HPC and cluster allows for up to liquid cooling cooling enables the installations with 50% less cooling infrastructure requires easy usage of waste more than 50 kW power and costs a way lower heat for heating per rack are only through high investment than homes, green houses, possible with efficient coolers traditional air cooled or swimming pools liquid cooling with low operating infrastructure costs 2 © 2015 Fujitsu Water as a Medium for Heat Transfer Removing the waste heat For 1000 W, 10 K temperature difference: 325 m³/ h of air 0,09 m³/h water Small water tubes can transport more heat than a room full of air! Heat transfer Heat transfer from water-to-water is better by a factor of 1,000 than water-to-air Cold plate and pump units are the same size or even smaller than regular heat sinks 3 © 2015 Fujitsu Fujitsu‘s Liquid Cooling Offering Future-proofing the Fujitsu PRIMERGY portfolio KW per rack will further rise and traditional air
  • System Technology

    System Technology

    System technology System technology ----------------------------------------------------------------------System technology List of contents INDOOR CLIMATE HEAT TRANSFER CLIMATE CONCEPTS COMFORT COOLING COOLING THE ROOM DESIGN WATER BASED CLIMATE SYSTEMS GUIDELINES 1 INDOOR CLIMATE ----------------------------------------------------------------------INDOOR CLIMATE PPD WHY CREATE A GOOD INDOOR CLIMATE % Experienced indoor climate 80 Individuals experience the climate as a joint action of several 60 factors that affect our thermal comfort: 40 • Level of activity, the body’s heat production 30 • Clothing’s thermal resistance • Ambient air temperature 20 • Surrounding surfaces’ temperature • The air’s relative speed 10 • The air’s relative humidity 8 6 According to professor P O Fanger the ideal indoor climate 4 has been attained when people perceive thermal comfort, i.e. –2,0 –1,5 –1,0 –0,5 0 0,5 1,51,0 2,0 PMV when a person is thermally neutral. However, one of the prob- lems you always face when creating a good climate with the Figure 1. Expected percentage of dissatisfied (PPD = Predict- help of a climate system is that people perceive the climate ed Percentage Dissatisfied) as a function of the thermal com- differently. fort perception (PMV = Predicted Mean Vote). No matter how well you succeed about 5% will still be dissat- -2 = cold isfied. The percentage of those dissatisfied will then increase -1 = slightly cold for each degree of deviation from the average person’s most ±0 = neutral ideal temperature. +1 = slightly warm +2 = hot Figure 1 shows the percentage of those dissatisfied when the temperature deviates from the average ideal temperature. Efficiency [%] Performance levels 100 What we consider to be the ideal indoor climate is always in- 90 dividual from person to person and studies show that per- formance levels follow a person’s perception.
  • The Installation of Direct Water-Cooling Systems to Reduce Cooling Energy Requirements for High-Performance Computing Centers

    The Installation of Direct Water-Cooling Systems to Reduce Cooling Energy Requirements for High-Performance Computing Centers

    The Installation of Direct Water-Cooling Systems to Reduce Cooling Energy Requirements for High-Performance Computing Centers Shankar Earni and Steve Greenberg, Lawrence Berkeley National Laboratory Walker Johnson, kW Engineering ABSTRACT A large cluster of High-Performance Computing (HPC) equipment at the Lawrence Livermore National Laboratory in California was retrofitted with an Asetek cooling system. The Asetek system is a hybrid scheme with water-cooled cold plates on high-heat-producing components in the information technology (IT) equipment, and with the remainder of the heat being removed by conventional air-cooling systems. In order to determine energy savings of the Asetek system, data were gathered and analyzed two ways: using top-down statistical models, and bottom-up engineering models. The cluster, “Cabernet”, rejected its heat into a facilities cooling water loop which in turn rejected the heat into the same chilled water system serving the computer-room air handlers (CRAHs) that provided the air-based cooling for the room. Because the “before” and “after” cases both reject their heat into the chilled water system, the only savings is due to reduction in CRAH fan power. The top-down analysis showed a 4% overall energy savings for the data center (power usage effectiveness (PUE) —the ratio of total data center energy to IT energy— dropped from 1.60 to 1.53, lower is better); the bottom-up analysis showed a 3% overall energy savings (PUE from 1.70 to 1.66) and an 11% savings for the Cabernet system by itself (partial PUE of 1.51). Greater savings, on the order of 15-20%, would be possible if the chilled water system was not used for rejecting the heat from the Asetek system.
  • Coordinating Liquid and Free Air Cooling with Workload Allocation for Data Center Power Minimization

    Coordinating Liquid and Free Air Cooling with Workload Allocation for Data Center Power Minimization

    COORDINATING LIQUID AND FREE AIR COOLING WITH WORKLOAD ALLOCATION FOR DATA CENTER POWER MINIMIZATION THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of the Ohio State University By Li Li Graduate Program in Electrical and Computer Engineering The Ohio State University 2014 Master's Examination Committee: Prof. Xiaorui Wang, Advisor Prof. F¨usun Ozg¨uner¨ c Copyright by Li Li 2014 ABSTRACT Data centers are seeking more efficient cooling techniques to reduce their operat- ing expenses, because cooling can account for 30-40% of the power consumption of a data center. Recently, liquid cooling has emerged as a promising alternative to tradi- tional air cooling, because it can help eliminate undesired air recirculation. Another emerging technology is free air cooling, which saves chiller power by utilizing outside cold air for cooling. Some existing data centers have already started to adopt both liquid and free air cooling techniques for significantly improved cooling efficiency and more data centers are expected to follow. In this thesis, we propose SmartCool, a power optimization scheme that effectively coordinates different cooling techniques and dynamically manages workload alloca- tion for jointly optimized cooling and server power. In sharp contrast to the existing work that addresses different cooling techniques in an isolated manner, SmartCool systematically formulates the integration of different cooling systems as a constrained optimization problem. Furthermore, since geo-distributed data centers have differ- ent ambient temperatures, SmartCool dynamically dispatches the incoming requests among a network of data centers with heterogeneous cooling systems to best leverage the high efficiency of free cooling.