Life-cycle optimal design and energy benefits of centralized cooling systems for data centers concerning progressive loading

Cooling of data centers requires a significant amount of energy, comparable to the energy consumption of the servers themselves. The current design of the centralized cooling systems for data centers is based on ideal IT loading conditions (i.e., 100 % loading). However, such conventional design often results in significant oversized cooling systems and leads to substantial energy waste, since most data centers operate at part load in their lifespan. To address this issue, this study proposes an optimal design for centralized cooling systems with multiple chillers under progressive loading. The optimization problem, aimed at minimizing life-cycle cost, is formulated adopting SLSQP (Sequential Least Squares Programming) algorithm. A cooling system model is developed using the manufacturer's performance data of cooling equipment. The optimal designs in different climate zones are identified according to energy performance under full-range loads and ambient temperatures. Furthermore, this study comprehensively analyzes and compares free cooling hours, cooling energy, and lifecycle cost of the optimized designs with conventional designs. 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.