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To better make use of the waste heat in distributed data centers, a new design of integrated waste heat recovery system that can meet different needs including heating for users and data center cooling is introduced. The system can switch among different operation modes including waste heat recovery mode, natural cooling mode, composite cooling mode and refrigeration mode based on the ambient temperature. The integrated waste heat recovery system is experimented in the enthalpy-difference laboratory, and the experimental results show well consistency compared with the modeling results. The operation strategies to switch among different modes are determined based on the experimental and modeling results. The paper introduced PUE (Power Usage Effectiveness) and ERE (Energy Reuse effectiveness) to comprehensively evaluate the cooling and energy reutilization effectiveness of the system. According to the evaluation result, the integrated waste heat recovery system has well performed energy effectiveness, environmental and economic effect. The ERE values of using the integrated waste heat recovery system in Chinese typical climate cities including Harbin, Beijing, Xi'an, Shanghai and Guangzhou are 0.87, 1.02, 1.04, 1.17 and 1.29 respectively. Using this system at 96 kW distributed data center instead of CRAC (computer room air conditioning) system can save 152.7 MWh electricity, 56.4 tons of standard coal, and 244.7 tons of CO 2 emission in Beijing annually. The payback periods of this new system in different climate regions in China are all within 3 years. • An integrated data center cooling and waste heat recovery system is proposed. • Operation performance of the system is verified by experiment and modeling. • Energy Reuse Factor in Beijing is 1.02, and payback period is within 3 years. [ABSTRACT FROM AUTHOR]

Recently, the rapid development of data centers has led to an increased requirement of cooling systems, resulting in high energy consumption. A two-phase thermosyphon loop (TPTL) system effectively utilizes a natural cold source and reduces energy consumption in data centers. In this study, an experiment was conducted to compare the heat transfer performance of CO 2 TPTL with the commonly used R134a and R410A TPTLs. Under their respective optimal filling ratios, CO 2 TPTL exhibited the lowest required driving temperature difference, which was 3 °C lower than that of R410A TPTL and 5 °C lower than that of R134a TPTL. The energy-saving effect of CO 2 TPTL was analyzed based on a typical data center case and the climate parameters of different cities in China. In Beijing, the annual average PUE (power usage effectiveness) of the data center using conventional centralized cooling systems, R134a TPTL, R410A TPTL, and CO 2 TPTL was 1.43, 1.36, 1.34, and 1.32, respectively. The calculation for other cities showed that the energy saving ratios of the CO 2 TPTL system in Kunming were the highest. They were 58.6%, 40.7%, and 30.4% higher compared with those of conventional centralized cooling system, R134a TPTL, and R410A TPTL, respectively. • Thermal performance of CO 2 , R134a and R410A TPTLs was compared by experiment. • PUE and CLF of the data center using different cooling systems were calculated. • CO 2 TPTL cooling system had the best energy-saving effect. • Energy consumption of the cooling systems in different cities was analyzed. [ABSTRACT FROM AUTHOR]