In this study, performance of the solar-thermal assisted air-conditioning system installed in an office building is investigated. In this paper, firstly the results of field measurements in winter (heating) and summer (cooling) are presented. Efficiency and performance of equipments which constitutes a system are investigated. Also the utilization efficiency of solar energy and the solar fraction are estimated for winter/summer season. In addition to analysis of field measurement data, system simulation of performance was conducted in this paper. Simulation program using in this study was developed as the tool for Life Cycle Energy Management of HVAC system. In this paper mathematical model of each equipment are presented as well as how to model total system . Although there are some limitations of solar system simulation with 1 hour time step, the calculation result was well in agreement in an actual measurement.