Building energy management and the necessity to reduce overall energy consumption is becoming an increasingly important topic. Especially in dynamic environments, where the setting and occupancy keep changing, knowing occupancy information, including the number and identities of the occupants and where they are located, can be beneficial in energy management as well as other application areas including safety, security and emergency response. In particular, occupancy information has a direct impact on various aspects of heating, ventilation, and air conditioning (HVAC) systems, such as heat loads, system running time, required heating, cooling and distribution of conditioned air, and preferred temperature set points. Energy-saving strategies can be carried out in response to real-time occupancy changes. In this paper, an RFID based occupancy detection system is proposed to support demand-driven HVAC operations by detecting and tracking multiple stationary and mobile occupants in multiple spaces simultaneously. The proposed system estimates the thermal zone where each occupant is located, and reports the number of occupants for each thermal zone in real time. The field tests yielded an average zone level detection accuracy of 88% for stationary occupants and 62% for mobile occupants. For scattering analysis, averages distances to corresponding centroids were 1.45 m and 3.24 m for stationary and mobile occupants, respectively. In order to explore the benefits of demand-driven HVAC operations, current HVAC work procedures are examined, major energy consumers in HVAC systems are identified and quantified, and energy-saving strategies are presented. This study aims to support reducing the consumption of the HVAC systems by integration of the occupancy detection system and the demand-driven HVAC operation strategies. (C) 2012 Elsevier B.V. All rights reserved.