For many years, rack density in data centers remained relatively stable. But in the past few years, it has started to rise significantly. According to the AFCOM State of the Data Center Report, average rack density increased from 7 kW per rack in 2021 to 8.5 kW in 2023, then to 12 kW in 2024, and now sits at 16 kW per rack.

This trend shows no signs of slowing. In fact, 79% of data center professionals expect further increases due to AI and other high-performance computing workloads. While some facilities are already running 50 kW racks and a few have surpassed 100 kW, those are still outliers. Even so, 68% of operators are actively working to support higher densities.

Some of the key strategies they are using to cope with higher densities include:

• Adopting liquid cooling (46%)
• Leveraging new sensors for enhanced visibility (38%)
• Improving airflow (51% of respondents)

Adopting Liquid Cooling

As rack density rises, so does interest in liquid cooling. One common approach is direct-to-chip (DTC) cooling, which uses cold plates to deliver liquid coolant directly to high-heat components like CPUs. This method supplements, rather than replaces, traditional air cooling. Fans are still needed to move air through the server.

Coolants range from water to dielectric fluids, each requiring proper plumbing and safety procedures.

Immersion cooling is another option, where entire servers or racks are submerged in dielectric fluid. This allows for highly efficient heat exchange, as the coolant is in direct contact with hot components. While some envision immersion cooling as the future for AI-focused data centers, it is important to remember that air cooling still plays a role. Heat removed from the servers is transferred to the immersion tank and eventually to the surrounding room. That heat must still be removed from the environment, which typically requires air-based systems.

Enhancing Visibility with Sensors

Deploying sensors throughout the data center helps operators monitor and optimize environmental conditions and infrastructure performance. Today’s sensors can track a wide range of variables including:

• Temperature and humidity
• Power quality
• Airflow and heat index
• Water leaks and flooding
• Smoke or fire
• Motion and access

These sensors can trigger alerts via text, email, or audio, or appear in centralized management systems. When integrated into platforms such as DCIM or AI-enabled analytics, they provide actionable insights to help fine-tune fan speeds, cooling unit output, and airflow paths.

As these technologies evolve, operators are gaining more precise control over how air and coolant are distributed throughout the data center.

Improving Airflow

According to the AFCOM report, improving airflow is the most common strategy being used to manage increasing rack density. This is not surprising, since airflow inefficiencies such as hot and cold air mixing, bypass airflow, and exhaust air recirculation are common and costly.

Optimizing airflow requires a comprehensive approach across four key areas:

1. Raised Floor: Seal cable openings with grommets or brushes, manage perforated tile placement, and inspect perimeter walls beneath the raised floor for unsealed penetrations. Use fire-rated materials to seal any gaps.

2. Rack: Eliminate open spaces along the vertical intake plane. Install blanking panels, rack grommets, and seals under cabinets and between mounting rails and cabinet sides.

3. Row: Block open spaces beneath racks, between cabinets, and wherever IT equipment is missing. For high-density areas or maximum efficiency, implement hot aisle or cold aisle containment.

4. Room: Adjust the cooling infrastructure by raising return air temperature setpoints, while staying within IT equipment specifications. Consider turning off underutilized cooling units, reducing fan speeds for those with variable frequency drives (VFDs), or installing VFDs where applicable. Monitor cooling performance and make ongoing adjustments to maintain efficiency.

As rack densities continue to rise, facilities that take a proactive, multi-faceted approach will be best equipped to keep up. Combining airflow optimization, real-time visibility, and advanced cooling technologies enables data centers to meet current demands and prepare for what is ahead.