Why CRAH Still Matters: The Essential Role of Air Cooling in Modern Data Centers

 • Liquid cooling does not eliminate the need for data center air cooling. Even liquid-cooled racks still release heat into the data hall, making efficient air-side cooling essential for stable data center operation.^[1]

 • CRAH is a core component of data center air cooling systems. Using chilled water from a central plant instead of a built-in compressor, it removes the remaining heat that liquid cooling leaves behind while supporting high-density IT environments.^[2]

 • As rack density increases, CRAH efficiency has a growing impact on data center energy consumption. Fan power and airflow design become major operating costs, making high-efficiency fans and low-resistance coils critical for reducing energy use.^[3]

 • LG's CRAH is designed for modern data centers, delivering approximately up to 405 kW of modular cooling capacity with a high-efficiency 3D Blade EC fan and oval coil design that may help reduce operating energy.

Liquid cooling is transforming how data centers handle heat, but it has not removed the need for air. Even in the most advanced liquid-cooled facilities, cold plates draw heat off the processors while the rest of the rack still vents heat into the room, and that heat has to go somewhere. According to Lawrence Berkeley National Laboratory (LBNL) under the U.S. Department of Energy’s data center energy efficiency program, liquid-cooled solutions are typically hybrid, with air cooling removing the share the liquid loop leaves behind.^[1]

 

That is where the computer room air handler, or CRAH, does its work. While liquid cooling manages high-density heat loads at the rack level, CRAHs remain essential for maintaining room-level cooling in liquid-cooled facilities and continue to serve as a primary cooling solution in many air-cooled data centers.

Room cooling still matters even though liquid cooling captures a large share of IT heat. Air-side cooling manages the remaining heat released into the data hall, helping maintain stable operating conditions. The U.S. Department of Energy's Center of Expertise for Data Center Energy Efficiency, run by Lawrence Berkeley National Laboratory, describes most liquid-cooled solutions as hybrid, where only part of the heat is removed by liquid and the rest is removed by traditional air cooling. In its own testing of direct-to-chip cold plates, the liquid loop typically captured around 50 to 60 percent of the heat, leaving the remainder to the air side.^[1]

 

That remainder is not trivial. Memory, power supplies, storage drives, and networking gear all shed heat into the room, and in a dense rack that adds up to a substantial cooling load on its own. As AI hardware pushes rack power higher, the total heat in the room rises with it. According to an International Energy Agency (IEA) report, the power density of AI servers increased approximately elevenfold between 2020 and 2025, with a further fourfold increase projected by 2027 under certain assumptions.^[2] Even when liquid takes the largest slice, the air-side slice grows in absolute terms as density climbs.

 

This is why room cooling remains important in the liquid cooling era, no less. A liquid loop that performs perfectly still cannot protect a room whose air side is undersized. The heat it leaves behind has nowhere to go, and temperatures climb regardless. Reliable high-density cooling depends on the air side being engineered with the same care as the liquid side.

A CRAH, or computer room air handler, is a precision cooling unit that removes heat from a data hall by passing warm room air over a chilled water coil. Cool water supplied by a central chiller plant runs through the coil, the unit's fans draw hot air across it, and the air gives up its heat to the water before returning to the room. The warmed water carries that heat back to the chiller plant to be rejected outside. Because the CRAH itself has no compressor, it is essentially a high-performance air-to-water heat exchanger with fans, and its chilled water valves and fan speeds can be tuned to the temperature of the air arriving at the racks.^[1]

 

That design is what separates a CRAH from its close relative, the CRAC. The distinction matters when sizing a facility. A CRAC, or computer room air conditioner, cools with its own built-in refrigerant compressor, which makes it self-contained and well suited to smaller rooms and edge sites. A CRAH has no compressor and instead relies on the central chiller plant, which makes it a common choice for larger facilities and campus-scale operations where a central plant is already in place. In systems where the central chiller plant incorporates free-cooling capability, CRAH units can take advantage of cool outdoor conditions to reduce reliance on mechanical refrigeration during favorable weather conditions.^[2]

 

CRAH serves as a key air-side component in high-density data halls. While the liquid loop draws heat straight off the processors, the CRAH manages the temperature of the whole room, clearing the residual heat from every component the liquid never touches and holding the space within the ranges IT equipment needs. It helps maintain the surrounding environment within ranges required for the dense racks enabled by liquid cooling.

One of the most important qualities in a modern CRAH is efficient air movement, because as racks get denser, the energy spent moving air becomes a major operating cost. ASHRAE notes that as servers grow denser, fan power can increase from less than 2% of total server power to around 10–20% in some high-density systems. In a 50kW rack, that corresponds to roughly 5–10 kW devoted to server fans alone^.[1] A CRAH that moves the required air with less fan energy can help lower that cost, which is why the features below deserve close attention.

 

When comparing CRAH units for a high-density hall, five factors matter most:

LG's CRAH is a modular fan-wall unit built specifically to be the air-side workhorse of a high-density hall, and it sits within a full LG hybrid portfolio that also includes Cold Plate and Coolant Distribution Unit products for the liquid side, so both the liquid-side and air-side cooling systems can be supplied by a single vendor as an option.*

 

*Actual performance depends on site conditions and workload.

 

At a glance, the unit offers:

 

 • Cooling capacity up to 490kW, delivered in a two-module lineup that can be customized to a data hall's dimensions.

 • Air handling capacity of approximately 100,000 CMH per unit, under design conditions.

*The required number of FWUs depends on the IT load and design conditions of the data hall.

 • Standard 380 to 480V power supply, for straightforward integration into facility electrical systems.

 • Designed for chilled water at 20/28°C, matching the central chiller plant it pairs with.

Liquid cooling has changed where a data center's heat is captured, but not the fact that the room still has to be cooled. While liquid cooling removes heat directly from targeted IT components, air-side cooling remains essential for managing the remaining heat within the data hall and maintaining stable operating conditions. The CRAH is the unit built for that job, using a chilled water coil and efficient fans to hold a high-density room within safe limits while keeping fan energy in check.

 

Treating the air side as a first-class part of the design, rather than an afterthought to the liquid loop, is what makes a high-density facility both reliable and efficient. A well-chosen CRAH, engineered for efficient airflow and coordinated with the rest of the system, can be an important factor in achieving reliable and efficient operation.