W45
ASHRAE's liquid-cooling classes keyed to maximum facility-water supply temperature, where a higher number means warmer water: less chiller capex and heat-reuse potential, less thermal headroom.
Also written as: W17 · W27 · W32 · W40
Current numbers
up to ~45 °C supply / ~65 °C return (W45-class)GB200 NVL72 coolant acceptance envelope — supply / return (ASHRAE W45-class); ~25 °C was NVIDIA's operating example, not a limit
~45 °Cwarm-water inlet band (W40/W45) GB200 & Rubin target — enables near-year-round chiller-less free cooling
up to ~45 °C supply / ~65 °C return (W45-class)GB200 NVL72 rack coolant acceptance envelope (ASHRAE W45-class) — warm-water operation is the design intent; colder supply buys thermal margin, at chiller cost