Servers have time constants on the order of several minutes, which is significantly longer than many other time constants observed in data centers. When server thermal masses are not negligible, transient scenarios cannot be modeled appropriately with the steady state boundary conditions. By using the time constant and thermal masses of the servers, transient server air exit temperature can be calculated by solving unsteady heat balance equations for the server and air stream. This paper presents a room-level CFD case study of rack shutdown in which transient server exit air temperature are introduced via user defined functions. The results include verification of simulation results with the experimental data taken in a 3-rack test cell.