Nowadays, an objective of different systems and technologies widely used in the HVAC systems is to provide acceptable quality of clean indoor air and comfort. The main reason of using mechanical ventilation in office buildings is to supply comfortable and healthy living environments for occupants, while maintaining minimum energy consumption. Electricity, which is the most expensive energy resource, is used in HVAC systems. Saving energy without changing the thermal comfort level would provide vast amount of profit considering operation costs. There are many measures which can be taken in this regard. In this study, experiments were hold in a climate chamber in the Department of Mechanical Engineering Heat Technology Laboratory in Uludag University, neck skin temperatures were measured and thermal sensations were questioned of subjects under different climate conditions. To evaluate the thermal comfort or discomfort "Predicted Mean Vote (PMV) index was used. After comparing the graphics obtained using the experiment results with the PMV values, optimum HVAC system operation conditions that yield profit without compromising thermal comfort are determined. In the conclusion optimum operation conditions for HVAC systems are suggested.