What Are Rear Door Heat Exchangers (RDHx)?

Benefits and Drawbacks of RDHx Compared to Other Cooling Systems

Rear door heat exchangers (RDHx) offer a unique blend of localized cooling, energy efficiency, and scalability. When evaluating RDHx technology, it is useful to compare it with other data center cooling methods, such as traditional Computer Room Air Conditioning (CRAC) units, in-row cooling, and liquid immersion cooling. Each system has distinct characteristics, and the choice depends on factors such as rack density, energy use goals, and facility design.

RDHx vs. CRAC (Computer Room Air Conditioning)

Traditional CRAC systems cool the entire room by conditioning the air that circulates throughout the data center. While effective for low-to-moderate density environments, CRAC systems often struggle to maintain thermal efficiency in high-density setups due to the mixing of hot and cold air. RDHx units cool the air directly at the rack level, preventing hot air from entering the room and reducing the overall demand on facility-wide heating, ventilation, and air conditioning (HVAC) systems. However, unlike CRAC systems, RDHx requires chilled water infrastructure and may involve more complex plumbing during deployment.

RDHx vs. In-Row Cooling

In-row cooling places cooling units between server racks, targeting hot air before it disperses into the room. This approach offers more precise airflow management than CRAC systems. Additionally, RDHx provides even more localized cooling by addressing heat at the rear of the rack itself, making it better suited for extremely high-density racks. On the other hand, in-row systems are often viewed as being easier to retrofit in some environments. As such, they may provide more flexibility in aisle containment strategies.

RDHx vs. Liquid Immersion Cooling

(RDHx does not overlap w/Immersion, whereas there is some overlap with DLC and should have its own paragraph/comparison)

Liquid immersion cooling involves submerging IT equipment in a thermally conductive dielectric fluid, offering excellent heat dissipation for very high-density systems. Although RDHx is less invasive in certain scenarios, this plus point is typically less significant in more modern IT setups where immersion-ready infrastructure is already in place. It is often compatible with legacy IT hardware, making it easier to deploy in traditional data centers. Nevertheless, RDHx simply cannot match the capacity of fully liquid-cooled systems and may not be suitable for ultra-high performance workloads requiring extreme thermal management.

Use Cases for RDHx in Modern Data Centers

Rear door heat exchangers are a versatile cooling solution suited to a range of deployment scenarios. Their ability to provide localized cooling at the rack level makes them especially valuable in environments where efficiency, density, and sustainability are top priorities.

In high-density server deployments, RDHx systems allow data centers to manage the significant heat output of densely packed racks without over-relying on room-level air conditioning. This localized approach enables operators to run more powerful hardware while maintaining thermal stability, often without the need for extensive HVAC upgrades.

Edge data centers also benefit from RDHx technology. These smaller, distributed facilities often operate in constrained spaces with limited access to traditional cooling infrastructure. RDHx units provide compact and efficient heat removal directly at the source, helping to ensure performance and reliability even in remote or non-traditional locations.

Sustainability-focused data centers increasingly adopt RDHx to reduce energy consumption and improve cooling efficiency. Because RDHx can work effectively with higher inlet water temperatures and supports the use of free cooling, it contributes to lower overall power usage and helps achieve aggressive environmental goals, such as reduced carbon footprint and improved PUE (Power Usage Effectiveness).

Legacy data centers that were not originally built to handle today’s thermal loads can also use RDHx as a retrofit solution. Rather than undergoing a full infrastructure overhaul, facilities can add RDHx units to existing racks to improve cooling performance. This allows for a degree of modernization with a data center refresh but without the advanced cooling efficacy of direct-to-chip liquid cooling and other, cutting-edge technologies.

FAQs

1. Is RDHx liquid cooling? 
   Yes, RDHx is a form of liquid cooling. It uses a liquid-to-air heat exchanger, typically with chilled water or another coolant, to absorb heat from server exhaust air. However, unlike direct-to-chip or immersion cooling, the liquid in RDHx systems does not come into direct contact with electronic components.
2. Why deploy RDHx in data centers? 
   RDHx systems offer localized, energy-efficient cooling at the rack level, which helps reduce the load on traditional HVAC systems. This leads to improved thermal performance, lower operating costs, and better support for high-density computing environments.
3. Can RDHx be installed in existing data centers? 
   Yes, RDHx can often be retrofitted onto existing server racks, making it a practical solution for legacy data centers looking to improve cooling efficiency without major infrastructure changes.