Go with the Flow: Is it Time Yet for Liquid Cooling?

But not for everyone. At least, not yet.

While hyperscale data centers will see significant growth in rack density, smaller enterprise and colocation data centers are forecasted to remain in the 12 KW – 17.5 KW levels for the next few years¹.

This suggests that there will be a transition period during which many operators can and will continue to use traditional chillers for cooling. Each method has its pros and cons. 

Air-Cooled Systems

On the plus side, air cooling is cost-effective, simple and reliable. It blows cold air across and around the hardware, causing the heat to dissipate and lowering the temperature inside the server.

Air-cooled systems are designed in three basic configurations.

• Room—The data center’s HVAC system drives cold air into the entire room or through vents in raised floors under the servers.
• Row—Airflow is targeted by dedicating an overhead cooling unit for each row of equipment. This is more efficient than cooling the entire room because less energy is needed to move the air over the servers.
• Rack—An even more focused approach, rack-based air-cooling systems target specific racks with their own cooling unit.

Also on the positive side, many data centers can help boost their HVAC system’s cooling capacity just by adding chillers or replacing their existing chiller with a more powerful one. Their HVAC technicians are typically familiar with chiller technology and understand how it works and how to maintain their systems.

The drawbacks? Although air cooling is enough for many data centers now, it may not be in the long term due to:

• The surging demand for data
• Rising cost of energy
• Water-related issues (particularly challenging for systems with large cooling towers)
  • Escalating water rates
  • Potential for water shortages

In addition to AI’s voracious appetite for computing power, rising energy costs—and even the cost of water for systems with large cooling towers—may be daunting challenges for data center operators with air-cooled systems.

Liquid Cooling

Instead of providing cooling at the room or row level, liquid cooling targets the heat right at its source: the servers. This technology can work in a few different ways.

• Direct-to-Chip Single Phase—This method delivers a liquid (usually water) to the CPU or GPU, with a cold plate in between so the electronics are never in contact with the fluid. Fans then blow in chilled air to move the tempered air away from the servers. The data center’s chiller still plays a major role with this type of liquid cooling.
  
  
• Rear Door Heat Exchanger—Here, a coolant-filled exchanger is mounted to the back of the server. An internal fan blows heat out of the server and across the exchanger, cooling it down before it’s released into the data center’s indoor air environment. Because it can be implemented without major modifications to the existing servers, it can be a cost-effective solution for data centers seeking to improve cooling.
  
  
• Immersion Cooling—With this technology, all server components are submerged in a tank of non-conductive liquid coolant. This dielectric fluid absorbs and dissipates heat, carrying the warmed fluid away from the components and into a cooling system. There, the heat is either expelled or further dissipated using other cooling methods. Immersion cooling offers high cooling efficiency compared to other liquid technologies. It’s also quieter, more energy-efficient and more compact, allowing for more densely packed hardware configurations.

While each type of liquid cooling system offers advantages, they have downsides as well.

• Initial costs are high due to the need for specialized equipment such as coolant tanks, pumps and heat exchangers. Even retrofitting existing equipment can incur additional investment.
  
  
• There’s always the risk of leaks, which can damage equipment and cause outages.
  
  
• Liquid cooling components require regular maintenance, including periodic fluid replacement.
  
  
• Certain hardware components cannot be used with liquid cooling systems due to their design and/ or materials.
  
  
• Systems are complex and require careful design, installation and maintenance, with special attention paid to proper sealing, plumbing and monitoring.
  
  
• Because it’s new technology, employees who are accustomed to maintaining air-cooled HVAC systems will experience a learning curve.

Whether you choose to stick with an air-cooled system or transition to liquid cooling—or implement a hybrid created from—Trane can help you develop, design, and operate the cooling system that keeps your data center up and running. 

^{1 JLL Research, 2024 - https://www.jll.com.co/en/trends-and-insights/research/data-center-outlook (Accessed April 2024)}