When does a data centre need liquid cooling instead of air?

Air cooling with good hot-aisle/cold-aisle containment works well for most racks, typically up to around 20–30 kW each. Above that, as with GPU servers for AI workloads, air struggles to remove the heat efficiently, and liquid cooling becomes a more practical option. Liquid cooling includes rear-door heat exchangers, direct-to-chip cold plates and immersion cooling, where servers sit in tanks of non-conductive fluid. Many sites run a hybrid, keeping air cooling for standard racks and adding liquid cooling only where densities demand it.