The Misconception: Liquid Cooling Doesn’t Eliminate Fan Requirements
When AI infrastructure teams first deploy liquid cooling — whether Rear Door Heat Exchangers (RDHx), direct liquid cooling (DLC), or immersion cooling — a common assumption is that fans become unnecessary. The reality is more nuanced. In hybrid liquid-air cooling architectures, which represent the vast majority of deployed AI data centers today, fans remain critical components in at least three distinct subsystems.
This guide explains where fans are still required, what specifications matter for each application, and how to select the right liquid cooling fan for AI server environments running NVIDIA DGX, Meta Grand Teton, OCP Open Rack v3, and similar platforms.
Where Fans Are Still Required in AI Liquid Cooling
1. Rear Door Heat Exchangers (RDHx)
RDHx systems mount water-cooled panels on the rear of server racks. Hot exhaust air from servers passes through the chilled panel, transferring heat to the building chilled water loop before it enters the data hall hot aisle. The RDHx panel itself creates airflow resistance — typically 150–300 Pa depending on fin density and chilled water temperature.
Servers alone cannot overcome this added resistance. Dedicated RDHx fans mounted in the door panel boost static pressure to push air through the heat exchanger matrix. For AI GPU racks dissipating 30–60 kW, fan arrays of 12–16 units in N+1 redundancy are standard, with each fan delivering ≥350 Pa static pressure.
2. Coolant Distribution Units (CDU)
CDU stations circulate chilled water or dielectric fluid to server cold plates. The CDU itself contains a coolant-to-air heat exchanger that rejects heat from the return loop before recirculating to the facility chilled water system — or in adiabatic configurations, directly to atmosphere. Fans in the CDU cabinet drive airflow across this internal heat exchanger.
CDU fan requirements depend on heat rejection capacity: 15–30 kW units typically use 92mm fans, while 40–100 kW CDU stations require 120mm or larger fans for adequate airflow volume at acceptable noise levels.
3. GPU Cold Plate Auxiliary Cooling
High-density GPU clusters (NVIDIA H100, H200, B200) use cold plates that contact the GPU die directly, but surrounding components — VRM voltage regulators, memory modules, NVLink bridges — still dissipate heat into the chassis airspace. Auxiliary fans maintain positive pressure within the chassis to prevent hotspot formation around these non-liquid-cooled components. These fans typically require 80–120 CFM at 200–300 Pa static pressure.
Critical Specifications for AI Liquid Cooling Fans
| Application | Size | Static Pressure | Airflow | Voltage | MTBF |
|---|---|---|---|---|---|
| RDHx Array | 92mm or 120mm | ≥350 Pa | 80–140 CFM | 48V DC | ≥50,000 h |
| CDU Cabinet | 120mm or 172mm | ≥300 Pa | 110–350 CFM | 48V DC | ≥50,000 h |
| GPU Auxiliary | 80mm or 92mm | ≥250 Pa | 60–100 CFM | 12V or 48V DC | ≥50,000 h |
Why 48V DC Matters for AI Data Centers
OCP Open Rack v3 standardizes on 48V DC power distribution throughout the rack. Native 48V DC fans eliminate the need for intermediate DC-DC converters, reducing power conversion losses by 3–5%, simplifying the power architecture, and enabling compatibility with OCP BBU (Battery Backup Unit) modules for ride-through during power events.
In large AI clusters (10,000+ GPUs), the cumulative efficiency gain from eliminating fan power converters represents meaningful power savings — and simplifies compliance with data center PUE targets.
Fengheng Technology Liquid Cooling Fan Portfolio
Fengheng Technology (Shenzhen) manufactures industrial-grade cooling fans for AI liquid cooling applications. The complete portfolio for RDHx, CDU, and auxiliary cooling:
- 92×25mm 48V DC — 8,000 RPM, 80 CFM, 350 Pa — RDHx arrays, compact CDU
- 120×25mm 48V DC — 5,500 RPM, 110 CFM, 380 Pa — CDU stations, OCP Open Rack v3
- 120×38mm 48V DC — 4,500 RPM, 140 CFM, 420 Pa — High-density RDHx, large CDU
- 172×51mm 48V DC — 3,200 RPM, 280 CFM, 480 Pa — 100 kW+ CDU stations
- 172×51mm EC — 0-10V/Modbus control, 350 CFM, 520 Pa — Building automation integrated CDU
- 240mm Radiator — 2,200 RPM, 180 CFM, 220 Pa — Edge AI liquid cooling loops
All models feature dual ball bearing construction (MTBF ≥50,000 hours), 4-pin PWM speed control, tachometer output, and CE/RoHS certification. 48V DC models are OCP Open Rack v3 compatible.
Need AI Server Liquid Cooling Fans?
Fengheng Technology supplies high-static-pressure 48V DC fans for RDHx, CDU stations, and GPU auxiliary cooling. Sample lead time: 2 weeks. Contact [email protected] or view the full AI liquid cooling fan portfolio →