In a typical data center, large numbers of IT sever racks are arranged in multiple rows. In IT environments, in which extensive electronic hardware is air-cooled, cooling system inefficiencies result when heated exhaust air from equipment prematurely mixes with chilled coolant air before it is used for cooling. Mixing of chilled air before it is used with heated exhaust air results in significant cooling inefficiencies in many systems. Over-temperatures may not only harm expensive electronic equipment but also interrupt critical and revenue generating services. The cool shield is a cost effective aisle partition system used to contain the air in cold aisles and hot aisles of an IT server room. This paper focuses on the use of performance metrics for analyzing a vertical aisle partition system in high-density data centers. Performance metrics provide a great opportunity for the data center industry at large. They could form the foundation for a standardized way of specifying and reporting various cooling solutions. The Rack Cooling Index (RCI) is a measure of how well the system cools the IT servers within the manufacturers' specifications, and the Return Temperature Index (RTI) is a measure of the energy performance of the air-management system. Combined, they provide an opportunity to judge the performance of the aisle partition system in an objective way subsequent to comprehensive CFD modeling. (C) 2011 Elsevier B.V. All rights reserved.