Coordinating Liquid and Free Air Cooling with Workload Allocation for Data Center Power Minimization

Data centers are seeking more efficient cooling techniques to reduce their operating expenses, because cooling can account for 30-40% of the power consumption of a data center. Recently, liquid cooling has emerged as a promising alternative to traditional air cooling, because it can help eliminate undesired air recirculation. Another emerging technology is free air cooling, which saves chiller power by utilizing outside cold air for cooling. Some existing data centers have already started to adopt both liquid and free air cooling techniques for significantly improved cooling efficiency and more data centers are expected to follow. In this paper, we propose SmartCool, a power optimization scheme that effectively coordinates different cooling techniques and dynamically manages workload allocation for jointly optimized cooling and server power. In sharp contrast to the existing work that addresses different cooling techniques in an isolated manner, SmartCool systematically formulates the integration of different cooling systems as a constrained optimization problem. Furthermore, since geo-distributed data centers have different ambient temperatures, SmartCool dynamically dispatches the incoming requests among a network of data centers with heterogeneous cooling systems to best leverage the high efficiency of free cooling. A light-weight heuristic algorithm is proposed to achieve a near-optimal solution with a low run-time overhead. We evaluate SmartCool both in simulation and on a hardware testbed. The results show that SmartCool outperforms two state-of-the-art baselines by having a 38% more power savings.