Being located in subtropical area, the weather in Taiwan is hot and humid which imposing huge cooling load on buildings. Conventionally, central air-conditioning plants were designed using refrigerant compressors to make chilled water, and then pumped through the zone pumps to meet the cooling load, providing air-conditioning by Fan Coil Unit (FCU) or Air-Handling Units (AHU) by ductwork. To meet the varying cooling demand, two important systems were developed for energy savings, namely, the Variable Water Volume (VWV) system, and the Variable Air Volume (VAV) system, which has been widely adapted in Taiwan area. The working principle is mainly devoted to adjusting the volume of the chilled water and/or air volume delivered through inverter-driven pimps and fans to achieve energy saving. On the other hand, recently in Japan, an important energy-saving air-conditioning system has been developed which directly varying the refrigerant flow rate to meet the varying cooling demand by inverter-driven compressors, named VRV system. Comparative to the conventional air-conditioning system, the heat exchange mechanism of the VRV system has been effectively enhanced by direct exchange of the refrigerant and the cool air, which is in effect a combination of the VWV and VAV system. It provided huge energy saving potential for the application on buildings with moderate cooling loads, such as 100 USRT or so. It is the goal of this research project, to evaluate the performance of the VRV system in Taiwan¡¦s hot and humid climate, by performing full-scale experimental investigation so that energy savings effect can be validated quantitatively. Since VRV system is fairly new in Taiwan, the validation of the system performance under local weather condition is of particular importance. It is anticipated that through the changing of the operation conditions, such as different outdoor conditions, various partial load conditions, and different scheduling of the VRV system, the power consumption of the VRV vs. conventional system can be compared precisely and quantitatively. These experimental data will, in turn, provides valuable reference to the establishment of the building energy consumption index in Taiwan, which outwits the direct adoption of the foreign data such as from Japan, in achieving a much reliable database.