Experimental characterization of the rear door fans and heat exchanger of a fully-enclosed, hybrid-cooled server cabinet

Abstract

A water-cooled, fully-enclosed server cabinet is one type of hybrid cooling technology used in data centers to cool high power IT equipment. These types of cabinets employ a water/air heat exchanger. External chilled water is provided to the heat exchanger and circulating air inside the cabinet is supplied to the server intakes. One advantage of this type of hybrid system is that the heat removed by the water-side can be used for other purposes, which is a potential means for increasing the overall data center energy efficiency. A specific commercial hybrid server cabinet design has been characterized experimentally in this study. The cabinet utilizes a V-shaped, unmixed-unmixed liquid-to-air cross flow heat exchanger. Three robust rear door mounted fans produce the air circulation in the cabinet. They are capable of providing an air flow rate of up to 1.321m3/s (2800 CFM) depending on the air temperature inside the cabinet. In the experiments, the air velocity is measured at different positions at the inlet and outlet of the heat exchanger using an array of velocity sensors. The contribution of each fan to the airflow distribution at the inlet of the heat exchanger is characterized using the measured air velocity data. For the water-side, the flow rate and temperature of the chilled water supply is measured using a vortex flow meter. From the measured air and water flow rates and temperatures, the effectiveness of the heat exchanger is calculated. The experimental results are presented in terms of effectiveness curves for different air and water operating flow rates and the high performance V-shaped heat exchanger is characterized in detail using these results. The heat exchanger performance data provides a better understanding of the design and operation of this type of closed cabinet, which can be used to potentially improve the operating efficiency.