The purpose of this study is to develop an optimization methodology for the detailed energy and cost effective design of a finned-tube condenser coil in order to enhance the system performance. Using this method, the frontal area of the condenser coil is maintained as constant, while other geometrical parameters of the thermal and economic performance of the system are varied and investigated. An existing air-cooled direct expansion (DX) rooftop package unit of a real-world commercial building is used for experimental data collection. First, the theoretical-empirical model for the system components is developed. Based on mathematical models and using collected data, a numerical algorithm is developed and embedded in a transient simulation tool. The integrated simulation tool is then validated by using the wide range of operating data obtained experimentally from the cooling plant during summer time. Furthermore, a mixed heuristic-deterministic optimization algorithm was implemented to determine the synthesis and design variables that influence the cost and energy efficiency of each configuration. Different new designs for condenser coil were then constructed to evaluate the potential of design improvements. Afterwards, the computer model was used to predict how changes in condenser coil geometry would affect the cost and energy consumption of the system. (C) 2014 Elsevier B.V. All rights reserved.