Cooling performance of ceiling-plenum-ducted containment systems in data centers

In an effort to improve the reliability and efficiency of data centers, racks and sometimes entire hot aisles are ducted to a dropped ceiling. The cooling performance of such systems strongly depends on IT and cooler airflow, the number and configuration of ducted objects and perforated ceiling tiles, the leakiness of the ceiling system, ceiling plenum depth, and other factors. Recently, a compact model has been proposed in which a Flow Network Model (FNM) representing the ducted equipment is embedded into a parent CFD model. By eliminating the need to explicitly model difficult-to-characterize leakage paths in CFD, this approach allows for realistic solutions while greatly improving the solutions speed and robustness of the CFD simulation. This paper employs the FNM (without CFD) to characterize and compare the cooling effectiveness of individually-ducted racks and ducted hot aisles subject to a given ceiling plenum pressure. Example resistance values needed in the FNM are provided. Additionally, an example data center layout is studied with the coupled FNM-CFD model to explore cooling performance as a function of ceiling leakiness, plenum depth, ratio of cooling to IT airflow, and rack density (IT airflow). Best-practice type recommendations for ducted equipment are provided.