Liquid to Liquid In-Row Coolant Distribution Unit Characterization for High Power Data Center
Authors: Shahi Pardeep , Heydari Ali , Modi Himanshu , Chinthaparthy Lochan Sai Reddy , Barigala Anto , Eslami Bahareh , Chowdhury Uschas , Agonafer Dereje , Tradat Mohammad , Rodriguez Jeremy 
Published: November 2024

Abstract
As the need for high-performance computing grows, data center operators have the challenge of regulating the increasing heat densities produced by current information technology equipment. Conventional air-based cooling systems are inadequate for dissipating the heat generated by high-power servers, prompting the exploration of alternative cooling techniques. The implementation of liquid cooling, particularly liquid-to-liquid cooling systems, has been identified as a potentially advantageous solution to addressing these issues. There are four distinct forms of liquid cooling technologies used in data centers. These include single-phase immersion cooling, two-phase immersion cooling, direct-to-chip liquid cooling employing single-phase micro-fin routed cold plates, and direct-to-chip liquid cooling employing two-phase cold plates. The coolant distribution unit (CDU) is an essential component of the liquid cooling system used in direct-to-chip liquid cooling technology. The CDU comprises a heat exchanger, circulating pumps, coolant monitoring sensors, and a Programmable Logic Controller that receives inputs and feedback from all coolant monitoring devices. The major function is to circulate the fluid, dissipate heat, and regulate the coolant’s supply temperature at a specific flow rate within the system. Alternatively, the CDU is tasked with regulating the temperature of the refrigerant supply. Testing is critical to ensure that the CDU performs at the desired level after installation. This article aims to outline several tests conducted on a CDU to evaluate its functionality and verify its proper operation. A coolant distributing unit is examined with a closed loop cooling system. The cooling system consists of two row manifolds, eight rack manifolds, and 32 cooling loops equipped on each of the 32 Thermal test vehicles. Thermal energy may be used to power the TTVs to a maximum of 200 KW. A suggested cleaning technique is followed to commission the CDU with the coolants at the start of the process. The tests involve operating the CDU in a variety of modes, such as pressure differential mode and flow control mode, at a range of coolant inlet temperatures that are suggested by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). An analysis is conducted on several realtime case scenarios, such as pump failure, low load operations, high load operations, and the response time of leak detection integrated into the CDU system. Accrediting liquid-to-liquid in-row coolant distribution systems is crucial to ensure the reliable and efficient functioning of high-power data centers. These advanced cooling technologies enhance data center performance, energy efficiency, and environmental sustainability in the current era of demanding computer workloads. They achieve this by effectively addressing thermal management-related challenges.