Air-to-Water Rear Door Cooler for High-Density Data Centers

An Air-to-Water Rear Door Cooler (RDC) is a high-efficiency, rack-mounted heat exchanger installed on the rear side of IT cabinets. It removes server exhaust heat directly at the rack level by transferring thermal energy from hot air to a closed-loop water circuit. Rear door coolers are widely adopted in high-density data centers where conventional room-based air conditioning is no longer sufficient or energy-efficient.

By cooling the exhaust air before it re-enters the data hall, an Air-to-Water Rear Door Cooler enables higher rack power densities, reduces reliance on CRAC/CRAH units, and significantly improves overall cooling effectiveness.

Working Principle

The Air-to-Water Rear Door Cooler operates on a simple and robust heat transfer principle:

1. Hot Air Capture
   Hot exhaust air discharged from servers flows directly into the rear door cooler.

2. Heat Exchange
   Inside the rear door, a finned tube or microchannel heat exchanger transfers heat from the air to circulating cooling water.

3. Air Discharge
   The cooled air exits the rear door at or near room temperature, minimizing hot aisle formation.

4. Water Heat Rejection
   The warmed water is routed to a heat rejection system such as a dry cooler, cooling tower, or chilled water loop.

This configuration allows the majority of IT heat to be removed without mixing with the data hall air.

Key Components

• High-efficiency air-to-water heat exchanger

• EC or passive airflow design (fan-assisted or fan-less)

• Stainless steel or aluminum frame construction

• Flexible hose connections or rigid piping interfaces

• Control valves, temperature sensors, and leak detection (optional)

Technical Advantages

• High Cooling Capacity

Rear door coolers can handle rack heat loads ranging from 20 kW to over 80 kW per rack, depending on water temperature and airflow design.

• Energy Efficiency

By using warm water cooling and free cooling sources, RDC systems significantly reduce compressor-based cooling energy and improve PUE.

• Modular and Scalable

Rear door coolers are deployed on a per-rack basis, making them ideal for phased expansions and mixed-density environments.

• Minimal White Space Impact

Installation does not require raised floors or major changes to existing air distribution systems.

• Support for High-Density IT

Well suited for AI, HPC, GPU clusters, and blade servers where traditional air cooling reaches its limits.

Typical Applications

• High-density enterprise data centers

• AI and HPC computing rooms

• Colocation facilities with mixed rack loads

• Edge data centers with limited space

• Retrofit projects requiring capacity upgrades

Integration with Data Center Cooling Systems

Air-to-Water Rear Door Coolers can be integrated with:

• Chilled water systems

• Warm water loops (18–45 °C supply)

• Dry coolers or adiabatic coolers

• Heat recovery systems for building heating or domestic hot water

This flexibility allows operators to optimize both capital and operational costs.

Design Considerations

• Water supply temperature and flow rate

• Rack airflow and server fan characteristics

• Pressure drop on air and water sides

• Redundancy and leak protection requirements

• Door weight and rack compatibility

Proper hydraulic and thermal design ensures stable operation and long service life.

Conclusion

The Air-to-Water Rear Door Cooler is a proven and future-ready cooling solution for modern data centers facing increasing rack power densities. By removing heat directly at the source, it enhances cooling efficiency, reduces energy consumption, and enables scalable growth without extensive infrastructure changes. For operators seeking a reliable path toward high-density and sustainable data center cooling, rear door cooling technology offers a compelling and cost-effective solution.