Cooling and Water Foundations for AI Infrastructure

Glossary

ASHRAE Thermal Guidelines

The reference published by ASHRAE technical committee TC 9.9 that sets recommended and allowable server inlet air conditions and the W-classes for liquid cooling supply temperatures.

Coolant distribution unit (CDU)

Equipment containing a heat exchanger, pumps, filters and controls that transfers heat from the server-side technology cooling loop to the building's facility water system while keeping the two loops separate.

Direct-to-chip liquid cooling

Cooling in which liquid flows through cold plates mounted on processors and other hot components, carrying heat away from the chip without relying on server airflow for those parts.

Dry cooler

A finned-coil heat exchanger that rejects heat to outdoor air with fans and no evaporation. It uses no water but can only cool fluid to a few degrees above ambient air temperature.

Immersion cooling

Cooling in which servers are submerged in a dielectric liquid. In single-phase systems the liquid stays liquid; in two-phase systems it boils on hot components and condenses on a coil.

Power usage effectiveness (PUE)

The ratio of total facility energy to the energy delivered to information technology equipment, defined by The Green Grid in 2007 and standardized as ISO/IEC 30134-2. Lower is better; 1.0 would mean zero overhead.

Water usage effectiveness (WUE)

Annual site water used for cooling and humidification divided by information technology equipment energy, in liters per kilowatt-hour. Introduced by The Green Grid in 2011 and standardized as ISO/IEC 30134-9.

Water withdrawal versus consumption

Withdrawal is all water taken from a source; consumption is the portion not returned, chiefly water evaporated. Evaporative cooling's main impact is consumption.