Data centres depend on precise environmental control. As server density increases, cooling decisions affect performance, energy use, and operational reliability. Two primary systems dominate the cooling landscape: CRAH and CRAC. While they appear similar in function, the underlying mechanisms and outcomes differ significantly. Understanding how each system works and where a liquid cooling system fits into the picture helps operators make better infrastructure choices.
Understanding CRAH Units
CRAH stands for Computer Room Air Handler. These units rely on chilled water from an external cooling system. They use fans to move air across a cooling coil. That chilled coil reduces air temperature before reintroducing it into the server room. CRAH units perform best in facilities with built-in liquid cooling systems like chillers or cooling towers.
CRAH units work by circulating air through raised flooring or ceiling spaces. The fans pull in warm air from servers and push cooled air back into the environment. Technicians managing large-scale data centres often choose CRAH setups for precise temperature control and consistent performance.
Chilled water-based systems deliver higher energy efficiency over time. Since CRAH units separate cooling medium (water) from air movement components, technicians can independently maintain both. That modular flexibility ensures fewer shutdowns and longer equipment life. Using CRAH also reduces reliance on mechanical refrigeration cycles, lowering power usage.
CRAH systems suit facilities with centralised cooling infrastructure. Their performance depends on available chilled water and integration with broader cooling architectures. Data centres with expanding rack density benefit from CRAH’s scalable performance, especially in combination with liquid cooling systems handling higher thermal loads.
Exploring CRAC Units
CRAC stands for Computer Room Air Conditioner. These units use direct expansion (DX) refrigeration cycles with internal compressors. Unlike CRAH, CRAC does not depend on external chilled water sources. Instead, CRAC units use refrigerant to absorb and expel heat directly.
CRAC units include fans, cooling coils, and refrigeration compressors. Warm air enters the unit, passes through evaporator coils filled with refrigerant, and exits as cold air. The system then discharges heat outdoors using condenser fans or external units.
Operators choose CRAC systems in facilities without chilled water infrastructure. These systems offer self-contained operation and minimal external dependency. CRAC units suit smaller data centres, network rooms, or edge facilities requiring standalone climate control.
However, CRAC units draw more energy per kilowatt of heat removed. That lowers efficiency compared to chilled water systems. With rising heat loads and increasing equipment density, CRAC struggles to match the long-term scalability that CRAH provides. Facilities that depend entirely on CRAC may encounter higher operational costs over time.
While CRAC simplifies installation and reduces initial setup costs, long-term performance tends to lag behind liquid-cooled CRAH environments. That performance gap becomes more evident in high-density environments where rapid, efficient heat removal becomes critical.
Comparing CRAH and CRAC in Application
CRAH and CRAC differ in cooling media, energy use, and operational design. CRAH uses chilled water from a central source, while CRAC relies on direct refrigerant cycling. CRAH allows integration into large-scale liquid cooling systems, offering better scalability for growing data demands.
CRAH units run more efficiently in high-density data centres, especially those implementing liquid cooling for advanced hardware. Large-scale facilities typically invest in chillers or cooling towers. These connect to CRAH units, distributing chilled water to multiple handlers. That network improves heat transfer efficiency and ensures stable conditions for sensitive hardware.
CRAC operates well in isolated environments. Small facilities or remote network hubs often benefit from CRAC due to the absence of centralised cooling plants. These setups require less infrastructure but limit temperature control as thermal loads rise. As rack densities grow, CRAC units need frequent upgrades or replacements to match cooling demands.
CRAH enables greater airflow management and supports hot aisle/cold aisle containment strategies. Combined with liquid cooling systems, CRAH contributes to maintaining narrow temperature tolerances while cutting operational overhead. CRAC, in contrast, remains static in design. Adjusting for expansion means installing extra units or investing in larger-capacity models.
Energy consumption also differs. CRAH draws less power when paired with efficient chillers and optimised airflow paths. CRAC, depending on internal compressors, burns more electricity during peak cooling cycles. Energy-sensitive environments find CRAH better suited for sustainability goals and long-term cost control.
Why the Difference Matters in Long-Term Cooling
Choosing between CRAH and CRAC has long-term consequences for operational efficiency, facility design, and cooling costs. CRAH aligns with facilities investing in a liquid cooling system to achieve high-efficiency cooling across scalable infrastructure. That integration creates predictable thermal management in line with data centre growth.
CRAH promotes future-ready expansion. Engineers can increase capacity without redesigning the entire HVAC framework. That flexibility reduces downtime and minimises long-term cost per kW of IT load. CRAH supports in-row or rear-door liquid cooling deployments, allowing precise cooling at the rack level.
CRAC works as a short-term or isolated solution. It simplifies installations in locations without water access or where infrastructure costs must remain low. Over time, however, CRAC presents operational challenges. Rising energy costs and maintenance needs undercut the early affordability.
Investors planning multi-megawatt facilities should consider CRAH paired with liquid cooling systems. That combination ensures performance, uptime, and energy efficiency. Small operators or edge environments may still find CRAC sufficient. But as IT loads increase, those facilities may face capacity bottlenecks and higher retrofit costs.
The decision impacts airflow dynamics, cooling redundancy, and hardware reliability. Data centres prioritising uptime, scalability, and energy conservation consistently choose CRAH over CRAC.
Conclusion
Selecting the right cooling solution requires understanding thermal demands, infrastructure layout, and long-term goals. CRAH systems, supported by liquid cooling infrastructure, deliver high-efficiency performance and flexibility for modern data environments. CRAC units serve limited roles in standalone settings but fall behind as density increases.
Organisations planning for scale, reliability, and energy control should evaluate CRAH systems alongside liquid cooling components. That approach guarantees better performance and lower lifecycle costs.
Contact Canatec for expert guidance on implementing a reliable liquid cooling system in Singapore that supports your data centre’s performance and expansion goals.