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• A new data center cooling system integrating heat recovery with free cooling is proposed. • The system can work selectively in four different modes according to conditions and demands. • Stable performance of each mode and dynamic performance in mode switching are obtained. • Annual power consumption and heat recovery analysis are conducted in five cities. Rapid growth of data centers has caused a huge increase in energy consumption. Utilizing natural cold resources and harvesting waste heat are two promising ways to reduce the total power consumption of data centers. This paper proposes an integrated system of free cooling and heat recovery. The system has four working modes: mechanical cooling, mechanical heat recovery, pump free cooling and pump heat recovery. Experimental results show that pump free cooling mode can achieve an energy efficiency ratio of 7.99 when outdoor temperature is 2 °C, and different modes can be switched smoothly. The applicability of this system has been evaluated in five different cities in China. The results show that annual average energy efficiency ratio can reach 6.18 and free cooling time can take up as high as 72.9% during operation in Xining. The system can harvest the most heat in Harbin, 7930.96 kW∙ h per year, while the least in Guangdong, 645.31 kW∙ h per year. This means that this new system has relatively great application prospects in northern cold cities of China, while is moderately limited in southern cities. [ABSTRACT FROM AUTHOR]

• A PEMFC-based CCHP system integrated with methanol reforming and dehumidification. • Realize the cooling and dehumidification of the data center simultaneously. • The dynamic performance under the cooling-led strategy is studied. • The temperature and humidity of the data center are controlled at 25 °C and 55–63%. For data centers with strict requirements on temperature and humidity, this study proposes a combined cooling, heating and power (CCHP) system integrated with methanol-reforming and dehumidification based on proton exchange membrane fuel cells (PEMFCs). The system consists of a methanol-reformer, preferential oxidation (PROX) reactor, PEMFC stack, adsorption chiller, desiccant air conditioning (DAC), and phase change material (PCM) heat storage tank. Taking a data center in Harbin as the research object, the dynamic response characteristics of the system are studied, and the system has good dynamic response characteristics. The CO concentration in the reformed gas is controlled by controlling the O 2 /CO ratio in the PROX. The CO concentration in the transformation gas can be controlled below 4 ppm. The cooling and dehumidification requirements of the data center are met by controlling the cooling power of the system and the air intake conditions of the data center. The results show that the cooling power of the system rises for 400 s at the beginning of the operation, and stabilizes after about 2 h, and the temperature and relative humidity of the data center can be controlled at 25 °C and 55–63%. The novel system develops an efficient way to recover low-grade waste heat of PEMFC stacks for cooling and dehumidification in data centers. [ABSTRACT FROM AUTHOR]