Why Data Center Efficiency Is No Longer Just About Power

When data center efficiency is discussed, many people still instinctively think in terms of “how much power is consumed” or “what the PUE looks like.” But in real-world data center operations, efficiency has never been a single-point issue.

While servers consume electricity, they also continuously generate heat. How that heat is removed in a stable and controllable way often determines whether the power system can truly operate efficiently.

As liquid cooling systems are introduced into next-generation data centers, the discussion around efficiency has expanded—from simply asking whether the power system is well designed to questioning whether power, cooling, and control are designed and operated within the same framework. In this process, PDUs and CDUs are increasingly becoming key factors that influence PUE.

Understanding PUE in Modern Data Centers

PUE remains one of the core metrics for measuring data center energy efficiency, but at its core, it is a result—not a root cause.

A high PUE does not necessarily mean the IT load itself is inefficient. More often, it reflects issues such as overly complex power distribution paths or significant “non-productive” energy consumption in the cooling system.

As cooling strategies evolve from purely air-based systems toward the introduction of liquid cooling, the composition of PUE also changes. Energy consumption that was once concentrated in fans and chiller systems is now partially shifted to liquid circulation, heat exchange, and coolant distribution.

PDUs: The Foundation of Electrical Efficiency

PDUs are among the most easily overlooked—but absolutely indispensable—components in a data center.

They do not participate in computation, yet they determine whether power can be delivered safely, reliably, and efficiently to every rack and every server.

In high-density environments, the value of a PDU extends beyond basic power delivery. It also includes:

• Whether power paths are clear and well defined

• Whether fine-grained power metering is supported

• Whether unnecessary conversion losses can be minimized

If power has already taken a “detour” before reaching IT equipment, even the most advanced cooling system will struggle to reduce overall PUE.

Where Efficiency Is Lost: From Power Distribution to Cooling Infrastructure

In practice, many efficiency losses do not occur within a single device, but at the boundaries between systems.

For example:

• Power distribution may be highly refined, while the cooling system lacks corresponding adjustment capability

• Server loads may fluctuate significantly, while the cooling side responds slowly

When liquid cooling is introduced, these system misalignments can become even more pronounced. This is because the coolant itself also requires energy to be pumped, regulated, and controlled.

Liquid Cooling Enters the Equation

Liquid cooling is not simply “a different cooling method”—it introduces new efficiency variables.

In a complete liquid cooling system, the coolant is no longer just a heat transfer medium; it becomes the core of the thermal management system.

Coolant flow rate, temperature differential, and stability directly affect:

• Chip temperatures

• Pump energy consumption

• Overall energy efficiency performance

This is why, in liquid-cooled environments, a purely power-centric perspective is no longer sufficient to explain changes in PUE.

What Is a CDU and Why It Matters

One of the most common questions when first encountering liquid cooling is: What is a CDU?

Simply put, a Coolant Distribution Unit (CDU) is the key component in a liquid cooling system responsible for delivering coolant to the right place, in the right amount, and under the right conditions.

If a liquid cooling system is compared to a municipal water supply network, the CDU is akin to a combination of a regional pumping station and a dispatch center.

It does not generate coolant, nor does it directly contact the chips—but it determines whether cooling is balanced, controllable, and efficient.

Coolant Distribution Units in the Data Center

In practical data center deployments, a CDU unit typically performs the following functions:

• Receiving coolant from the primary cooling source or a secondary loop

• Distributing coolant to different racks or servers based on load demand

• Controlling flow rate, pressure, and temperature windows

From an engineering perspective, the design of a coolant distribution unit directly affects system stability. Uneven distribution can result in some equipment being overcooled while others operate near thermal limits—ultimately increasing overall energy consumption.

CDU in the Data Center Power and Cooling Balance

In a CDU-based data center architecture, the cooling system is no longer merely an accessory to the power system.

The operating state of the CDU can, in turn, influence power delivery strategies and overall efficiency.

For example:

• Increased CDU pump power is reflected in auxiliary energy consumption

• Inefficient cooling distribution may force IT equipment to reduce performance or rely on additional redundancy

As a result, data center CDU planning often needs to be carried out in parallel with PDU and power architecture design, rather than being added as an afterthought.

Measuring What Matters: PDUs, CDUs, and Real Efficiency Visibility

Truly controllable efficiency comes from visibility.

PDUs provide transparency on the power side, while CDUs provide transparency on the cooling side. Only when the two are combined does PUE become more than just a number on a report.

When power load, cooling load, and IT load can be understood within a unified monitoring framework, optimization shifts from guesswork to fact-based adjustment.

Common Pitfalls When Evaluating Efficiency in Liquid-Cooled Data Centers

After liquid cooling is introduced, common pitfalls include:

• Focusing only on server temperatures while ignoring cooling distribution efficiency

• Looking solely at overall PUE without visibility into CDU-level energy consumption

• Assuming liquid cooling is “automatically more efficient” while overlooking system design quality

These issues often do not appear in design documents, but gradually surface after months of operation.

Building a Balanced Infrastructure: Power, Cooling, and Control

An efficient data center is not one where a single system is exceptionally advanced, but one where all systems are well balanced.

PDUs ensure power is delivered properly, CDUs ensure heat is removed effectively, and control systems ensure both operate within optimal ranges.

When these three elements form a closed loop, efficiency becomes stable and sustainable—rather than something maintained through constant manual intervention.

How ATTOM Supports PDU and CDU Integration in Liquid-Cooled Data Centers

In liquid-cooled data center projects, ATTOM focuses not on individual devices, but on end-to-end infrastructure coordination.

From power distribution designs that support liquid-cooled loads to cooling distribution strategies aligned with CDUs, ATTOM delivers system-level, deployment-ready support—helping customers introduce liquid cooling while maintaining a balance between energy efficiency and operational reliability.