Dynamic models for server rack and CRAH in a room level CFD model of a data center

In this work dynamic numerical models for server, rack, and Computer Room Air Handler (CRAH) are developed and used in a room level Computational Fluid Dynamics (CFD) model. The effect of server, rack, and Computer Room Air Handler (CRAH) heat capacity is investigated in cases of server power fluctuations and CRAH failure situations. The room level numerical model used in this analysis is an experimentally verified model that has been developed in previous studies for steady state analysis. The model takes into account the calibrated fan curves for servers and cooling units, and a detailed model for a rack to address the potential leakage locations. A validated lumped mass model is used to simulate the heat capacity of a server based on available experimental data. The server level model is utilized in room level CFD simulations. The heat capacity of rack chassis is also modeled in this study based on a detailed rack model. A validated analytical model for a CRAH cooling coil using manufacturer data is developed. Two CFD models simulating the CRAH cooling coil are also developed and the lumped mass model is used for transient simulations in case of CRAH failure. An order of magnitude increase is observed in the time constant associated with change in temperature compared with models that neglects the effect of server and CRAH heat capacity. It is also found that the rack chassis heat capacity has a slight influence on temperatures rate of change, thus it can be neglected without affecting the accuracy of the results and also reducing the computational time.

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