With rising rack densities, AI-driven workloads, and increasing demands for improved energy efficiency, traditional cooling methods are reaching their limits. Among the technologies gaining attention are rear door heat exchangers (RDHx), but despite their growing adoption, misconceptions persist.

A clear understanding of RDHx technology is essential for data center operators seeking to evaluate how best to future-proof their facilities.

What are rear door heat exchangers?

Rear door heat exchangers are liquid-based, air-assisted cooling systems mounted on the rear of server racks to remove heat at its source.

Ambient air enters the rack through IT equipment fans, and the resulting hot exhaust air passes over a heat exchanger, assisted by EC fans in the RDHx chassis. The heat is transferred to a liquid-cooling fluid, and the cooled air is expelled back into the room at or just below the set room’s ambient temperature.

By removing heat at the source, RDHx systems reduce dependence on room-level cooling and maintain stable thermal conditions even as power densities increase. This targeted approach meets current demands for more efficient cooling over traditional cooling.

Myth 1: Rear door heat exchangers are too expensive

A common assumption is that RDHx systems have prohibitive upfront costs compared to traditional cooling systems. While initial capital expenditure may be slightly higher, this view often overlooks the total cost of ownership, as long-term energy and maintenance savings provide a strong ROI.

By removing heat directly at its source, RDHx systems reduce fan energy, overcooling, and overall power consumption. This energy-efficient design delivers operational savings, especially in high-density environments where traditional air-cooling systems are less effective.

RDHx systems also require less maintenance than conventional systems, further reducing costs. When evaluated from a long-term efficiency and sustainability perspective, RDHx compares favorably to traditional alternatives.

Myth 2: RDHx systems are complex and hard to maintain

Another misconception is that RDHx systems are complex to install and maintain. In fact, leading RDHx systems are designed for simplicity and ease of use.

Unlike traditional cooling systems that often require complex maintenance and specialized technicians, RDHx systems are low-maintenance. Advanced models feature user-friendly interfaces and intuitive controls, allowing data center operators to monitor and manage performance without specialist support.

Myth 3: RDHx aren’t compatible with existing infrastructure

Some believe that RDHx systems require major modifications to existing data center infrastructure to deploy. In practice, best-in-class RDHx systems are highly compatible and integrate seamlessly with a wide range of server racks and cooling systems, making them ideal for hybrid environments where both high-density and legacy infrastructure exist.

Advanced RDHx systems can be easily retrofitted to legacy equipment or installed in new data centers. This flexibility minimizes operational disruption and enables incremental upgrades without major modifications.

A strategic tool for high-density computing

As AI, HPC, and edge computing reshape data center design, cooling has become a strategic priority rather than just a facilities concern.

RDHx systems are increasingly valuable tools for thermal management, enabling data centers to support the next generation of AI advancements without compromising efficiency or performance.

By addressing outdated assumptions about cost, complexity, and compatibility, data center leaders can better determine how RDHx supports their broader efficiency, sustainability, and scalability goals.

Enhancing cooling efficiency with Legrand’s ColdLogik RDHx

RDHx technology, shown by ColdLogik RDHx from USystems (a brand of Legrand), highlights how targeted, liquid-based, air-assisted cooling can scale to support long-term efficiency and higher rack densities.

At the University of Cambridge’s West Cambridge Data Centre, ColdLogik RDHx forms part of a hybrid cooling strategy supporting HPC workloads. The deployment enabled cabinet power densities to increase from approximately 30kW to 44kW per rack, and data hall capacity to rise from 900kW to 1.2MW, without compromising thermal stability or cooling efficiency.

The RDHx solution works with chilled water, glycol, and air-cooled systems, enabling 100 percent free-cooling operation with hybrid dry coolers. This approach removes heat at source, reduces reliance on room-level cooling, and eliminates operational water use through a closed-loop design, supporting both low-PUE and zero-WUE cooling strategies.

With the ability to remove up to 200kW of heat per rack, ColdLogik RDHx shows how rear-door heat exchangers enable higher-density, AI-ready environments while maintaining efficiency, resilience, and sustainability. The system can be deployed in existing data center infrastructure, reinforcing RDHx’s role as a scalable, practical solution for modernizing data centers rather than requiring a disruptive overhaul. As facilities evolve to support AI and other high-performance workloads, this flexibility supports improved performance, resilience, and long-term environmental goals.

For more information on Legrand’s ColdLogik RDHx, visit the Legrand website.