There are in total about 1.9 million air conditioners (ACs) in Taiwan, and during the summer time the energy consumption of these ACs is about 30% of total country energy consumption. Therefore, effective energy management of these ACs is an essential task to energy saving and carbon reduction. The purpose of this paper is thus to design and to develop an energy billing and demand control system for buildings with aggregated ACs, such as schools, company offices, factories, apartments, etc. The system presented in this paper consists of a power meter, an RFID billing reader, and a demand control module with infrared remote control and relay control. Computer GUI for supervisory control and data acquisition (SCADA) and energy management is also developed. Based on the experimental results, the demand variations of ACs indeed follow the commands sent from the presented system, and the fluctuation of the room temperature is not large during the demand control period.