Data center cooling removes the enormous heat that servers and IT equipment produce, keeping them within safe temperatures and the facility running efficiently. It has become one of the most important — and fastest-changing — parts of data center design, as soaring AI and GPU power densities push traditional air cooling past its limits and drive a shift toward liquid. This guide covers how data centers are cooled, from air conditioning to direct-to-chip and immersion liquid cooling, and the chillers and distribution systems behind them.
What is data center cooling?
Data center cooling is the collection of systems that capture and reject the heat generated by computing equipment. Every watt a server consumes ends up as heat, and that heat must be removed continuously to prevent equipment from overheating, throttling, or failing. Cooling directly affects three things data center operators care about most: uptime, equipment life, and energy efficiency — cooling is one of the largest non-IT energy costs in a facility.
Why cooling matters more than ever
The demands on cooling are rising sharply. AI and machine-learning hardware packs far more power into each rack than traditional servers, and that concentrated heat is difficult to remove with air alone. At the same time, operators are under pressure to improve efficiency, measured by PUE (Power Usage Effectiveness) — the ratio of total facility energy to IT energy. Since cooling is a major share of the overhead, better cooling is one of the most direct ways to lower PUE and energy cost. These twin pressures — higher density and tighter efficiency — are reshaping how data centers are cooled.
Air cooling methods
For decades, data centers have been cooled primarily by air. The familiar approaches include:
- CRAC / CRAH units — computer room air conditioners and air handlers that cool and circulate room air, often through a raised floor.
- Hot-aisle / cold-aisle containment — arranging racks so cold supply air and hot exhaust air are kept separate, improving efficiency.
- In-row and rack-level air cooling — placing cooling closer to the racks to handle higher densities.
Air cooling is well understood and works well at moderate densities. Its limitation is physics: air carries relatively little heat, so as racks grow hotter, air cooling needs ever more airflow and eventually cannot keep up.
Liquid cooling methods
To handle modern densities, data centers are turning to liquid cooling, which brings coolant far closer to the heat. The main approaches are:
Direct-to-chip (cold plate)
A cold plate is mounted directly on the processor or GPU, and coolant flowing through it carries heat away to a coolant distribution unit and the facility system. Direct-to-chip cooling targets the hottest components precisely and is a leading choice for AI hardware.
Immersion cooling
Servers are submerged in a thermally conductive, electrically non-conductive fluid that absorbs heat directly. In single-phase immersion the fluid stays liquid; in two-phase immersion it boils and condenses to move heat. Immersion is highly effective and removes the need for server fans, but requires specialized tanks and fluids.
Rear-door heat exchangers
A liquid-cooled heat exchanger is fitted to the back of a rack, cooling the hot exhaust air as it leaves. This is a practical way to add liquid-cooling capacity to existing air-cooled rooms.
Free cooling and efficiency
Because cooling energy is so significant, data centers use techniques to cut it wherever possible. Economizers use cool outside air or water when ambient conditions allow, reducing or avoiding mechanical refrigeration. Adiabatic and evaporative cooling use the cooling effect of water evaporation to boost efficiency. And chilled-water systems with efficient chillers form the backbone of many large facilities. Together these approaches push PUE down toward the ideal of 1.0.
The cooling infrastructure: chillers, CDUs, and heat exchangers
Behind every cooling approach is the infrastructure that produces and moves the coolant. Chillers generate chilled fluid; coolant distribution units (CDUs) isolate and manage the liquid loop that serves the IT equipment, controlling flow, temperature, and pressure; and heat exchangers transfer heat between loops. In a liquid-cooled data center, a CDU typically separates the clean technology coolant from the facility water, running the IT side as a controlled closed loop. The CDU is important enough that it deserves its own discussion as the heart of liquid cooling.
Eldrotec liquid cooling for high-density applications
Eldrotec designs and manufactures the building blocks that high-density and liquid cooling depend on: precision chillers, custom heat exchangers and hydronics — pumps, manifolds, piping, and connectors that form coolant distribution and closed-loop systems — engineered to each application’s heat load and conditions. Built to AS9100 and MIL-STD standards with thermal modelling and simulation, these systems suit high-density, edge, and custom cooling requirements. Contact the engineering team to discuss a liquid cooling solution for your environment.
Frequently Asked Questions
What is data center cooling?
Data center cooling is the set of systems that remove the heat generated by servers and IT equipment, keeping them within safe operating temperatures. It is essential to uptime, equipment life, and energy efficiency, and ranges from traditional air conditioning of the room to advanced liquid cooling that brings coolant directly to the hottest components.
Why are data centers moving to liquid cooling?
Rising rack power densities — driven especially by AI and GPU hardware — generate more heat than air cooling can practically remove. Liquid carries far more heat than air, so liquid cooling can handle these high densities efficiently, in a smaller footprint and often with lower energy use, which is why data centers are adopting it.
What is the difference between air and liquid cooling in data centers?
Air cooling moves cool air through the room and across servers using units such as CRAC/CRAH systems and aisle containment. Liquid cooling brings coolant much closer to the heat — to cold plates on the chips or by immersing hardware in fluid — removing far more heat per unit. Air suits lower densities; liquid is needed for high-density and AI workloads.
What is direct-to-chip (cold plate) cooling?
Direct-to-chip cooling mounts a cold plate — a metal plate with internal coolant channels — directly onto a processor or GPU. Coolant flowing through the plate carries heat away to a coolant distribution unit and the facility’s cooling system. It targets the hottest components precisely and is a leading approach for AI hardware.
What is immersion cooling?
Immersion cooling submerges servers in a thermally conductive, electrically non-conductive fluid that absorbs their heat directly. In single-phase immersion the fluid stays liquid; in two-phase immersion it boils and condenses to move heat. It removes heat very effectively and eliminates server fans, but requires specialized tanks and fluids.
What is PUE in data center cooling?
PUE, or Power Usage Effectiveness, is the ratio of a data center’s total energy use to the energy used by its IT equipment alone. A PUE closer to 1.0 means less energy spent on overhead such as cooling. Because cooling is a major part of that overhead, efficient cooling is central to improving PUE.