Thermal mass characterization of a server at different fan speeds

Abstract

Dynamic cooling has been proposed as one approach for enhancing the energy efficiency of data center facilities. It involves using sensors to closely monitor the data center environment with time and making real time decisions on how to allocate the cooling resources based on the location of hotspots and concentration of workloads. In order to effectively implement this approach, it is good to know the transient thermal response of the various systems comprising the data center must be determined, which is a function of thermal mass. Not only is thermal mass important in dynamic cooling, it also plays a major role in the temperature rise of a data center during power failure. A previous study concentrated on characterizing the thermal mass of a 2 RU server by running the server at different powers and a fixed fan speed. The fixed fan speed corresponds to one specific heat transfer coefficient value. This study is a continuation to the previous work, where the server fan speed is varied to deduce the change in heat transfer coefficient at different airflow rates. As expected, the heat transfer coefficient increases as the server airflow rate increases. The average thermal mass value obtained for the 2 RU server in this study was 12 kJ/K. A method of adopting the compact model developed in this study into a Computational Fluid Dynamics (CFD) code is proposed to cut down on the computational time of transient analysis.