High-Density Rack Cooling Challenges
Facing high-density racks of 100–130kW or more (such as NVL72), the chiller serves as the “heat exchange heart” on the facility side. Through dual-loop isolation design, 15–25°C high-temperature supply water to prevent condensation, free cooling, and second-level variable-frequency regulation, it ensures GPUs with 700–1200W TDP can sustain full load operation without throttling, achieving an annual PUE (Power Usage Effectiveness) ≤1.15.
Item | Specification |
Rack Power Density | 100～130kW |
Single Chip Thermal Design Power (TDP) | 700～1200W |
Chiller Supply Water Temperature | 15～25°C（high temperature anti-condensation） |
Annual Target PUE | ≤1.15 |
Dual-Loop Heat Exchange Architecture
● Primary Side TCS (Chip Side): Cold plates tightly attached to GPUs absorb heat. Coolant flows through the cold plates, carrying away heat, using ~30–45°C deionized water or PGW (propylene glycol water solution) as the working fluid, which returns to the CDU for liquid–liquid heat exchange.
● Intermediate CDU: Equipped with plate heat exchangers for liquid–liquid exchange. Micro-pressure isolation ensures no leakage into the motherboard loop while maintaining coolant purity.
● Secondary Side FWS (Facility Side): Chiller provides 15–25°C chilled water to absorb heat.
● Final Heat Rejection: Cooling towers or dry coolers release waste heat to the atmosphere via evaporative latent heat or finned air cooling.
Four Core Mechanisms of Chillers
Core Mechanism | Technical Challenge | Control Strategy and Advantages |
Extreme Heat Flux | In AI servers or HPC environments, single chips (e.g., GPUs) generate highly concentrated heat, typically 700–1200W TDP. | High-flow, low-resistance water loop design with CDU optimization reduces local overheating risks. |
Precise Water Temperature Control | Traditional 7°C chilled water may fall below ambient dew point, causing condensation risks. | Maintaining supply water at 15–25°C effectively prevents condensation. |
Free Cooling | Continuous compressor operation increases energy consumption and PUE. | By expanding allowable chip water temperature to 25–35°C, free cooling/heat exchanger modes are prioritized in cooler seasons, reducing compressor usage and achieving PUE ≤1.15. |
Second-Level Load Tracking | In AI data centers or high-performance computing environments, the cooling system can respond within seconds to drastic server load fluctuations, maintaining stable water temperature and heat dissipation, and preventing GPU or CPU from throttling due to sudden overheating. | Using magnetic-bearing oil-free centrifugal or variable-frequency twin-screw compressors, adjustments can be completed within 3–5 seconds, keeping water temperature fluctuations within ±0.5°C. |
Comparison of Mainstream Chiller System Types
System Type | Architecture Features | Core Advantages | Limitations & Challenges |
Water-Cooled Chiller + Cooling Tower | Heat rejected outdoors via cooling tower using evaporative latent heat. | COP ≥6.0, highest efficiency, small footprint. | High water consumption, requires chemical treatment, risk of freezing in winter. |
Air-Cooled Chiller (with Free Cooling) | Condenser integrates fans and fins, refrigerant directly rejects heat to air. | Zero water use, modular deployment, no water treatment. | Efficiency drops in summer, large rooftop footprint, noise issues. |
Hybrid Dry Cooler System (Hybrid Chiller) | Dry cooler handles cooling in cold seasons; chiller activates in hot seasons. | Optimal annual PUE, water-saving, stable, longer lifespan. | Complex piping, PLC control requirements, high initial CAPEX. |
Future Evolution Trends
● Short Term: The emergence of two-phase immersion cooling will transform the chiller’s role into a “precision cold source.” Chillers act as stable cold sources for top condenser coils, maintaining micro-pressure and vapor–liquid balance in sealed chambers. In high-temperature or special scenarios, chillers remain indispensable, thus increasing their value.
● Long Term: With dry coolers and warm-water cooling (35–45°C) maturing, most seasons will rely on dry coolers or free cooling as the primary heat rejection method. Chillers may shift to auxiliary equipment, reducing demand, but still serve as a safeguard in extreme environments.
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