Data Center Cooling Evolution: CRAC, CRAH, Fan Wall and RDHx Liquid Cooling Solutions
The next milestone in our technical roadmap focuses on hall-level data center cooling infrastructure. Mainstream air-cooled equipment includes CRAC units, CRAH units and fan wall systems, while direct expansion (DX) units are rarely deployed in modern facilities. As a professional rear door heat exchanger supplier, we systematically analyze the differences between traditional air cooling and emerging rack-level liquid cooling technologies to support high-density AI data center construction and upgrading.
CRAC and CRAH represent two generations of traditional data center air-cooling architectures with distinct operating principles and application scenarios. CRAC runs an independent refrigerant circulation system paired with external condensing units, featuring simple structure but limited cooling capacity (up to 100kW) and low energy efficiency, suitable for small-scale legacy data centers. As a mature rack door heat exchanger alternative, centralized CRAH systems connect multiple air handlers to building chilled water loops, delivering better long-term economy for large data centers with fewer moving parts and stable operation.
Modern large-scale data centers increasingly adopt fan wall systems to replace traditional CRAH units, boasting a single-unit cooling capacity of 500–600kW and modular stacking design that supports 5–10MW hall-level cooling demands. Fan walls eliminate the need for raised floors and perforated tiles, drawing hot air from mechanical corridors instead of ceiling return air. Optimized for ultra-large computing clusters, this air-cooled architecture perfectly complements our heat exchanger rear door rack cooling system, forming a hybrid cooling layout for diversified load requirements.
Redundant configuration is a core guarantee for Tier 3 equivalent data center reliability. CRAC, CRAH and fan wall systems generally adopt N+1 or N+2 equipment redundancy, while water supply pipelines deploy 2N architecture to support isolated maintenance and fault switching. In pursuit of higher cooling efficiency for upgraded rack density, the rear door heat exchanger cooling solution has gained rapid popularity, serving as a rack-level precision cooling upgrade of traditional CRAH systems.
The rear door heat exchanger (RDHx) is installed on the rear side of server racks, utilizing circulating chilled water to absorb heat from air-cooled IT equipment. Passive RDHx supports 30–40kW per rack, while active fan-enhanced models exceed 50kW, widely adopted in high-density AI clusters such as xAI’s Memphis data center. As a professional liquid rear door cooler manufacturer, we optimize RDHx heat exchange efficiency up to 0.8, surpassing the 0.6–0.7 efficiency of conventional CRAH and fan wall systems, allowing higher chilled water inlet temperatures to reduce chiller energy consumption.
RDHx delivers outstanding precision cooling advantages yet comes with inherent cost and power consumption tradeoffs. Multiple small fans used in rack-level cooling consume more power than centralized large fans, and increased moving parts raise capital expenditure. In partial liquid cooling renovation scenarios, the matched coolant manifold rear door heat exchanger and CDU (Coolant Distribution Unit) are required to precisely regulate flow rate, temperature and pressure drop, ensuring stable and balanced operation of the entire rack liquid cooling loop.
CDU acts as the core heat transfer hub for rack-level liquid cooling, conducting heat exchange between the internal IT cooling loop and external building chilled water loop, with single-unit capacity exceeding 1MW. Paired with RDHx equipment, the complete rack rear door liquid cooling system solves the heat dissipation bottleneck of 40kW+ high-density racks, realizing seamless switching between air cooling and hybrid air-liquid cooling for both legacy room renovation and new data center construction.
Chillers serve as the core energy-consuming equipment of data center cooling systems, divided into air-cooled and water-cooled types. Water-cooled chillers support ultra-large capacity up to 20MW with high COP energy efficiency, requiring cooling towers for heat dissipation. Wet cooling towers deliver powerful cooling performance in dry regions, while dry towers achieve zero water consumption for environmentally sensitive scenarios. Our complete product portfolio covers customizable and export data center rear door heat exchanger solutions, matching various chiller systems to build low-PUE, high-reliability green data center cooling infrastructure worldwide.
EXTRCOOL delivers the liquid cooling infrastructure you need: CDUs, cold plates, manifolds, and piping, available as standard products or custom-engineered to your precise requirements. Our solutions maximize thermal efficiency while minimizing environmental impact, with a proven track record at gigawatt-scale deployments worldwide. When performance and uptime are on the line, EXTRCOOL is the name you trust.
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