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Engineering

Why AI racks need liquid

For thirty years a data centre was a room with cold air in it. Accelerator racks ended that. Somewhere above thirty kilowatts in a rack, air stops being an engineering choice and becomes an argument with physics, and the building has to change shape.

Why AI racks need liquidEngineering

Air stops working somewhere around thirty kilowatts in a rack. What replaces it, and what it does to the building.

Where air gives out

Air carries little heat per unit volume, so removing more of it means moving more air, faster. Fan power rises steeply, noise rises with it, and containment gets harder to hold. Conventional halls sit comfortably in the single-digit kilowatts per rack. Modern accelerator rows are specified many times higher. That gap is not closed by better fans.

What replaces it

Liquid takes the heat where it is made. Direct-to-chip puts a cold plate on the processor and runs coolant to it through a distribution unit that separates the technical loop from the building's. Rear-door heat exchangers cool the air as it leaves the rack, which suits a retrofit. Immersion puts the hardware in fluid entirely. The three differ in how much of the building they demand, and how much of the customer's hardware they dictate.

What it does to the building

Liquid changes floor loading, plant room, risers and the maintenance regime. It also changes the temperature of what leaves – and that is the part worth designing for. Direct-to-chip returns warmer water than an air-cooled hall ever produced, and warmer water is what makes waste heat sellable rather than merely rejected. A cooling decision is a heat decision taken early.

The honest limit

Liquid is not free efficiency. It adds a fluid circuit to a building that must never lose one, it demands a maintenance culture more than a product, and it constrains what a tenant may install. We design the environment and draw the boundary at the rack. What crosses that boundary is contractual, and saying so is more useful to a customer than claiming to support everything.

Sources

  1. 01ASHRAE – thermal guidelines for data processing environments, and the liquid cooling classes
  2. 02Energieeffizienzgesetz (EnEfG) – the efficiency obligations that make cooling a legal question

Where else to go.

The rest of the site, including the parts a diligence reader wants and the parts the law requires.

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