Energy savings in direct air-side free cooling data centers: A cross-system modeling and optimization framework

The advancement of intelligent technology has led to a significant increase in the electricity consumption of data centers. Efficient free cooling and cross-system optimization are major means to improve data center energy efficiency. This work aims to develop a cross-system modeling and optimization methodology to reduce the energy consumption within data centers equipped with direct air-side economizer. A series of physics-based models are built, accounting for free cooling costs, supply air conditions (including both temperature and humidity), and outdoor weather fluctuations. A holistic energy optimization framework is proposed to determine optimal system setpoints that accommodate changes in computing workload arrival rates and outdoor environments. Experimental results demonstrate that the optimal cost characteristic curve for free cooling can be represented as a piecewise function. The advantages of the proposed method can save up to more than 5% of overall energy, which occurs during summer weeks, and more than 46% of cooling energy during winter weeks. The highest share of cooling energy consumption is the supply air fan, reaching up to more than 92% in some situations. The operation of a direct air-side economizer is found to contain four optimal modes.