Comprehensive Guide to Rack Cooling in Data Centers

With the rapid growth of AI, high-performance computing (HPC), and cloud services, data center power density is rising faster than ever before. As server performance increases, so does the amount of heat they generate — and thermal management has become a critical factor affecting both the stability and energy efficiency of data center operations.Rack cooling systems have therefore emerged as one of the most essential and effective thermal management solutions in modern data centers.

Why Rack Cooling Matters

In traditional data centers, cooling was primarily handled by room-level air conditioning systems (CRAC/CRAH) that lowered the overall room temperature. However, as rack power density has climbed from a few kilowatts to 20–30 kW or more, this “whole-room” cooling approach has become insufficient for managing localized heat buildup.

Rack cooling shifts the focus from room-level to cabinet-level precision cooling, delivering cold air directly to the heat source and recovering hot air immediately at the rack.

This close-coupled cooling method not only improves thermal efficiency but also reduces energy consumption and maintenance costs — making it the ideal solution for high-density computing and sustainable data center operations.

How Rack Cooling Works

At the core of rack cooling is the concept of “close-proximity cooling.”Through controlled airflow or liquid-cooled modules, the system directs the cooling medium precisely to the server’s heat-generating components, achieving localized, fast, and targeted heat exchange.

Typically, cold air enters the rack from the front or bottom, absorbs heat as it passes through the servers, and exits from the rear. Some systems incorporate cooling coils or rear-door heat exchangers that immediately cool the exhaust air and return it to circulation.

In higher-density environments, rack cooling systems may also integrate liquid circulation loops, using chilled water or glycol solutions to carry away heat, thereby further enhancing cooling efficiency.

Common Types of Rack Cooling

• In-Row Cooling:Cooling units are placed between racks, creating a short, efficient airflow path. Cold air is delivered directly to server inlets, while hot air is captured at the rear. This setup offers high efficiency and low energy consumption — ideal for medium to high-density environments.
•  Rear Door Heat Exchanger (RDHx):A liquid-cooled door is mounted on the back of the rack to absorb heat as air exits. RDHx requires no additional floor space and can significantly enhance cooling performance without altering existing room-level air conditioning layouts.
• In-Rack Cooling:Cooling modules are integrated directly inside the cabinet, using liquid cooling coils or sealed air circulation. This method provides precise, high-efficiency cooling for high-density servers and HPC applications.

Key Considerations for Deploying Rack Cooling Systems

• Thermal Load Assessment: Identify rack-level power distribution and peak heat output to ensure sufficient cooling redundancy.

• Airflow Optimization: Design proper hot-aisle and cold-aisle containment to prevent hot air recirculation.

• Space and Piping Layout: Coordinate placement of cooling units, piping, and cabling to avoid maintenance conflicts.

• Coolant and Safety Management: For liquid systems, incorporate leak detection and emergency drainage mechanisms.

• Intelligent Monitoring: Use sensors and monitoring platforms for real-time tracking of temperature, flow rate, and pressure with automated alerts.

With proper design and integration, rack cooling systems can effectively control temperature, extend equipment lifespan, and significantly improve energy utilization.

Future Trend: The Convergence of Rack and Liquid Cooling

As GPU clusters and AI computing centers become mainstream, rack power densities are approaching 40 kW and beyond.
The future of data center cooling will no longer be a binary choice between air and liquid systems — but a hybrid architecture that combines both:

• Rack cooling handles medium-power zones,

• Liquid cooling (such as Direct-to-Chip or immersion systems) supports ultra-dense computing nodes.

Together, they form a layered thermal management ecosystem, maximizing overall cooling efficiency while enabling modular scalability and sustainable infrastructure growth.

Attom Rack Cooling Solutions

Attom offers a full portfolio of rack-level cooling products and integrated systems — including in-row cooling, rear-door heat exchangers, and in-rack liquid cooling architectures.

Whether for new AI training centers or upgrading traditional facilities, Attom delivers efficient, safe, and sustainable rack cooling solutions that help data centers stay cool, stable, and high-performing in the era of high-density computing.