Cooling Distribution Unit

Overview

A Cooling Distribution Unit (CDU) is the central component of a direct-to-chip liquid cooling system. It conditions facility water or facility chilled water (primary loop) and circulates precision-temperature, precision-flow coolant to server cold plates via the secondary loop. CDUs are available in two major configurations: liquid-to-liquid (in-row, for data centers with chilled water infrastructure) and liquid-to-air (in-row or sidecar, for facilities without chilled water). Cooling capacity ranges from approximately 100 kW for sidecar/in-row units to 2.5 MW for large in-row models.

For AI training deployments, CDU control logic must handle frequently varying GPU thermal loads across training stages — a requirement beyond conventional CDU designs that target steady-state server loads. Key performance metrics include approach temperature differential (ATD), flow rate range and stability, redundancy configuration (N+1 for pumps, fans, and power supplies), and behavior during failure switchover.

Envicool's largest in-row liquid-to-liquid CDU delivers 2500 kW at 4°C ATD with 3750 LPM at 35 psi, N+1 power supply redundancy, wide flow rate range (1%–100%), and less than 5% fluctuation during failure switchover.