Effect of transient boundary conditions and detailed thermal modeling of data center rooms

With the ever increasing heat loads dissipated by computer hardware, the ability to accurately characterize the cooling requirements in data centers is becoming crucial. Computational fluid dynamics modeling has proven in many cases to be adequate in providing a general understanding of the thermal environment in data centers. However, almost all analyses of data centers to this day are conducted in steady state. The effect of changes in hardware configurations and cooling resources on server rack inlet temperatures and airflow through servers has not been adequately investigated. This paper introduces transient modeling of data centers with changing power dissipations and computer room air-conditioning (CRAC) airflow rates. Transient modeling proves advantageous in monitoring temperature fluctuations due to airflow changes, which in some cases leads to insufficient cooling. In addition, modeling server thermal mass is shown to be important for transient analysis, as it can lead to overshoots in temperatures. Another segment of this paper looks at the effect of introducing thermal characteristics curves into CRAC modeling on server inlet temperature. All the cases presented show that fixed CRAC supply temperature is a non-valid assumption.