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This paper presents a method to evaluate air flow effectiveness of both traditional raised floor designs and non-raised floor air-conditioning designs for data centers. Metrics are developed that will easily permit owners, engineers and operators to measure and quantify the performance of their data center air distribution systems or changes that they make to their cooling systems to improve air management and hence cooling system efficiency. The metrics incorporate and integrate together the major factors that decrease the effectiveness of computer room air cooling. These metrics, which are covered in the paper, include; negative pressure flow rate (air induced into the floor void), bypass flow rate (from floor void directly back to the air-conditioners without cooling servers), recirculation flow rate (from server outlet, back into server inlet) and the balance of CRAC and server design flow rates. Examples of the application of these metrics are also presented. Additionally, benchmarking data of bypass and recirculation collected from over 60 data centers during energy audits are presented. The benchmarking data clearly identifies potential energy saving opportunities when compared to ideal (no bypass and no recirculation). Consequently, one can use the benchmarking data to compare a given data center to others and to measure progress in reducing recirculation and bypass levels as energy conservation measures and best design practices are implemented in the data center. The methodology presented in this paper offers the advantage to establish quick understanding of the air management in the data center in fairly short amount of time using internal resources once the presented guidelines and lessons learned are followed. Performing CFD, which may be required in some cases, requires specialized engineers with sufficient knowledge in data center air flow paths, racks and server types, cooling equipment and power distribution units in order to build reliable air flow- - models using any of the commercially available CFD packages. The aforementioned requirements render the CFD simulation an expensive service. Hence, CFD simulation should be used when air management analysis falls short, example of such cases include planning for future IT growth using specific hardware in specific location.