Experimental characterization and modeling of a water-cooled server cabinet

Water-cooled server racks are typically closed cabinets, so no heat load is removed by the room cooling system in a raised floor data center. Instead, the cooling is provided by a closed system employing an air-water (fin-tube) heat exchanger. This kind of heat exchanger uses chilled water from a central plant, and there is the potential of using the waste heat that is returned. The goal of this study is characterize a specific sealed-door, water-cooled server cabinet under steady state and transient operation. The experimental part of the study is being performed on a Knurr CoolThermTM® rack. In this cabinet, the water/air heat exchanger is located at the bottom. Cooling air is circulated by three rear door mounted fans, the cooled air flows upward in front of the servers. The specific cabinet being tested has the capability to handle 25 kW and has a 30% cooling system energy efficiency. In the experiments, 16 1U servers and a 9U load bank are employed for generating a heat load. Over 100 thermocouples are used to monitor air temperature within different parts of the cabinet. The operating conditions monitored include: water flow rate, water inlet temperature, air flow rate through the servers, air flow rate through the heat exchanger, air temperatures and server power. The internal temperature of the servers is also monitored. From the measured data, the effectiveness is calculated for four different water flow rates and different power dissipation levels. Computational modeling of the air flow and heat transfer in a simplified model of the cabinet is also performed.