Liquid cooling

Liquid cooling is the use of fluids instead of air to remove heat from IT equipment, exploiting the fact that water conducts heat roughly 25 times better than air and carries far more heat per unit volume. Main approaches include direct-to-chip cold plates, rear-door heat exchangers (liquid-cooled doors on standard racks), and immersion cooling. Liquid cooling becomes practically necessary above roughly 40-50 kW per rack and is mandatory for modern AI hardware: NVIDIA's GB200 NVL72 rack at around 120-130 kW is liquid-cooled by design. Benefits include support for extreme density, lower fan energy, better PUE (often below 1.2), and heat-reuse potential from warm return water. The shift to liquid is reshaping colocation, as legacy air-cooled halls require costly retrofits with coolant distribution units (CDUs) and new piping.