| Author: | Zhang, Yingbo |
| Title: | Global energy performance assessment and optimization of data center cooling systems |
| Advisors: | Wang, Shengwei (BEEE) |
| Degree: | Ph.D. |
| Year: | 2025 |
| Department: | Department of Building Environment and Energy Engineering |
| Pages: | xviii, 160 pages : color illustrations |
| Language: | English |
| Abstract: | As the digital backbone of our increasingly interconnected world, energy-intensive data centers pose a significant challenge to global decarbonization. Global data center electricity use in 2021 was 220-320 TWh, around 0.9%-1.3% of global electricity demand. The energy use per square foot in data centers can be 100 times that of typical office buildings. Notably, the cooling energy required to keep the servers in data centers from overheating is on par with that of the servers themselves, representing 30%-40% of the total energy consumption of data centers. Developing highly efficient cooling systems in data centers is a key challenge for the decarbonization of the data center industry. Therefore, this study aims to conduct a comprehensive assessment of the energy performance of data centers and develop cutting-edge methods or technologies to fundamentally improve the energy efficiency of data centers. Firstly, a thorough review of next-generation high-temperature data centers and the categorization of existing methods/strategies for enhancing the energy efficiency of data center cooling systems is conducted. Secondly, the global energy impact of high-temperature data centers is comprehensively assessed. Thirdly, the energy performance of data center cooling systems under various conditions is analyzed systematically. A comprehensive methodology for the optimal design of data center cooling systems is developed considering progressive loading and life-cycle energy performance. Fourthly, the optimal dispatch strategy and design scenario for energy storage systems in data centers are investigated to unlock their great flexibility for smart grid services. Lastly, the energy, economic and carbon impacts of the national initiative 'Eastern Data, Western Computing' are assessed comprehensively by analyzing three major migration routes. To tackle the problem of high and increasing data center energy consumption, high-temperature data center is proposed as a fundamental solution. It adopts a different cooling mechanism and makes 'chiller-free' data centers possible, facilitating the transition from chiller-based cooling to completely-free cooling in data centers. This study conducts a comprehensive review of high-temperature data centers, especially their key advantages and the primary challenges associated with their implementation, as well as the existing efforts and latest technologies to tackle the bottlenecks. Future perspectives for the development and applications of the high-temperature data center are also discussed. Furthermore, the global energy impacts of high-temperature data centers are quantified and analyzed. The trade-off between cooling energy savings and server power rise is critically analyzed and discussed. Moreover, quantitative guidance and targets for developing 'ideal' and 'recommendable' servers for high-temperature data centers are established for IT and server professionals to further develop IT equipment and servers that take the data center cooling energy into account. When raising the space temperature to 41°C (namely, the 'global free-cooling temperature'), nearly all the land area can achieve 100% free cooling year-round globally. Operating at this space temperature, up to 56% cooling-energy savings could be achieved compared with operating at the current typical space temperature of 22°C. To develop a life-cycle optimal design for data center cooling systems, the energy performance of data center cooling systems is systematically analyzed under full-range cooling loads and climate conditions. The energy performance of typical cooling systems is quantified under a typical progressive loading throughout the data center's lifecycle. An optimal design method is developed for centralized cooling systems with multiple chillers under progressive loading. The optimal designs in different climate zones are determined according to the energy performance under full-range loads and ambient temperatures. Free cooling hours, cooling energy, and life-cycle costs of the optimized designs and conventional designs are analyzed and compared comprehensively. The results show that the optimized cooling systems could operate more energy-efficiently, despite decreased free cooling hours (13-860). Significant cooling energy savings over the lifespan could be achieved, i.e., 4-22%, corresponding to the PUE reductions of 0.02-0.11, depending on climate conditions and control strategies. This study also pioneers the idea of utilizing surplus energy storage capacity in data centers to offer grid flexibility services, considering progressive loading throughout their lifecycle. Two optimization problems are formulated for optimal energy storage dispatch in operation and for storage system design optimization respectively. The objective for optimal dispatch is to minimize the electricity cost, by efficiently allocating battery and cold storage capacities. The objective for design optimization is to minimize the life-cycle costs including investments and operation cost savings under typical loading conditions and electricity markets. Two typical electricity markets (the Guangdong electricity market and the CAISO electricity market) and four investment scenarios for energy storage systems are considered. The impacts of discount rates and battery prices on the life-cycle economic benefits of energy storage systems are also analyzed comprehensively. The participation of data centers in grid flexibility services demonstrates significant economic benefits. Over its lifetime, the battery storage can achieve economic benefits of $1.6 million, which is 1.29 times its total investment. The cold storage can achieve economic benefits of $0.35 million, which is 2.39 times its total investment. To facilitate the decarbonization of data centers, the Chinese government launched an ambitious initiative, called 'Eastern Data, Western Computing'. The national initiative aims to migrate computing workloads from electricity-deficient Eastern regions to renewable-rich Western regions. A comprehensive assessment is conducted concerning its energy, economic and carbon impacts by analyzing three major migration routes. Future perspectives and challenges on carbon emission reduction of the initiative are analyzed. Potential policy suggestions and actionable insights are proposed to address these challenges. We found that 'moving bits' is much more energy efficient than 'moving watts', but not necessarily beneficial for decarbonization. The national initiative shows significant energy-saving potential, 332-942 GWh (4.8-12.5%) annually, attributed to reduced cooling energy and eliminated power-transmission loss. However, no economic benefit is observed if considering the high capital costs for constructing duplicated data centers in Western regions. The carbon emission benefits in different routes are significantly different. Shanghai-Sichuan route could reduce carbon emissions by up to 2803 KtCO₂e (79.6%) annually, whereas Beijing-Inner Mongolia route exhibits a notable increase (1164 KtCO₂e (24.9%)) in carbon emissions. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/13606