Free cooling in data centers: Principles, technologies, and applications

Free-cooling is a central strategy in data center thermal management to reduce cooling energy use and improve system efficiency. This chapter reviews major free-cooling approaches, including conduction-, convection-, and radiation-based methods, with air-side and water-side economizers dominating current practice. Advances in information technology hardware tolerance and the adoption of liquid cooling have expanded allowable operating temperatures, enabling broader and more flexible use of economizer-based cooling. The growth of artificial intelligence workloads further enhances free-cooling potential by enabling location-aware siting, workload scheduling aligned with favorable ambient conditions, and the deployment of high-density, liquid-cooled infrastructures. These developments support a transition from opportunistic free-cooling to coordinated, system-level strategies that integrate workload, cooling, and environmental conditions. Future systems are expected to adopt more adaptive control and high-capacity heat rejection pathways, positioning free-cooling as a foundational component of next-generation data center design.