Supercritical Carbon Dioxide Brayton Power Cycle is getting commercially attractive for power generation due to its numerous advantages like zero water discharge, compactness, low environmental emission and potential to reach high thermal efficiency. A typical recuperated closed cycle consists of three heat exchangers (main heat exchanger, cooler and recuperator) and two turbomachinery (turbine and compressor). The cooler using ambient air for cooling is the focus of this study. Steady state air cooler model is set up to study the effect of air cooler size on cycle efficiency. The effect of change in ambient air temperature on air cooler pinch point for different air cooler sizes is analyzed using transient air cooler model. The simulation is setup for design of approximately 100MWe cycle with operating temperature of 700°C and pressure of 250 bara. Transient calculations are done using LMS AMESim. LMS AMESim is Siemens PLM commercially available software. This work thus serves as a framework to develop a basis for design of air cooler in the power cycle as a function of transient operating conditions.