Experimental investigation of a dual-evaporator pump-driven loop heat pipe composite system for data centers cooling

Data centers are highly energy-intensive facilities, with cooling systems accounting for 30 % of total energy consumption. To reduce this energy consumption, natural cooling sources can be fully utilized, commonly through pumped loop heat pipe composite systems. However, such systems employ the same evaporator across different modes, resulting in untapped potential for natural cooling. Therefore, this study proposes a dual-evaporator pumped loop heat pipe (DePLHP) composite system for data center cooling, featuring three adaptive operational modes: pumped loop heat pipe (PLHP) mode, composite mode, and vapor compression (VC) mode. These modes automatically switch based on outdoor temperatures, optimizing energy efficiency through maximal natural cooling utilization and supplemental mechanical assistance when required. Experimental validation in a climate-controlled enthalpy difference chamber confirmed superior performance. Compared to conventional PLHP systems, the system achieved 20.3 % and 13.3 % energy savings at 15 °C and 25 °C respectively while maintaining high energy efficiency ratios (EER) across most operating conditions. Compliance with the national standard GB 40879-2021 was verified. Application analysis across 12 representative Chinese cities spanning diverse climates demonstrates robust adaptability. The system attained an average annual energy efficiency ratio (AEER) of 7.78 across cities, with power usage effectiveness (PUE) averaging between 1.22 and 1.31 depending on auxiliary equipment energy ratios. A load-responsive mode-switching control strategy was proposed for partial-load conditions, further enhancing AEER. In summary, the proposed system delivers exceptional energy-saving performance and holds significant importance for green data center development.