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In recent years, water-side free cooling has been broadly applied in data centers to lessen the high cost of energy consumption. The energy-saving opportunities of free cooling have been recognized by numerous studies across the world. In this paper, the field test and energy performance evaluation were performed in an operational data center with water-side free cooling, located in Chongqing, China. Existing problems were found during tests, including the insufficient cooling capacity of towers in wintertime and the inability to activate partial-free cooling. The results of the tests show that the reduction in Power Usage Effectiveness (PUE) is much lower than the expected. To understand the marked discrepancies, the performance of the cooling tower was discussed in terms of the approach temperature and actual cooling capacity. The maximum cooling capacity in winter is only about 50 % of the rated. With the consideration of the cooling tower configuration performance in different climate conditions, the conservative energy effects were calculated in 34 provincial cities of China. To prolong the hours available, optimized operation schemes of cooling towers are presented. The available hours for free cooling could be increased from 730 h to 1300 h when operating at 67 % of rated flow rate, resulting in a decrease in the energy saving of chillers between 8.44 % and 21.05 %. [ABSTRACT FROM AUTHOR]

• Field measurements and simulation method were employed. • Tests and analyzes the thermal environment of a data center in Chongqing. • 77 cases were simulated to investigate servers' arrangement and air distribution strategy under partial load. • Inlet air temperature of racks and SHI value were regarded as the criteria for thermal environment. In recent years, with the rapid development of data centers, its huge energy consumption problem is increasingly prominent. Especially, with the development trend of large-scale data center, the load rate of racks is relatively low, which can easily lead to oversupply of cold capacity, thus resulting in energy waste. Hence, how to reasonably arrange servers so as to effectively utilize cooling capacity and improve energy efficiency has become an urgent problem to be solved. In this paper, field test was made to investigate the thermal environment. The test results indicated that the actual load rate of the data room is between 19.34%˜42.55%, and SHI value for test rows were between 0.128 and 0.594 owning to oversupply of CRACs, as a result of serious mixing of cold air and hot air. To reduce the energy consumption, the cooling capacity of CRACs were equal to IT equipment heat dissipation by using simulation tool through changing the load rate, servers' arrangement and air distribution strategy under partial load in data centers. The results showed that the servers uniformly distributed in all racks presented good inlet air temperature that fell in the acceptable temperature range by ASHRAE. And it suggests that the servers are uniformly mounted from the middle of the rack and then the upper for low load rates. When the load rate more than 60%, blanking plates need to be installed. [ABSTRACT FROM AUTHOR]