For an air conditioned building, the major electricity consumption is by the heating, and air conditioning (HVAC) system. As energy saving strategies may be in conflict with the criteria of indoor air quality and thermal comfort, a concept of the building environmental performance model (BEPM) has been developed to optimize energy consumption in HVAC systems without any deterioration of the indoor air quality and thermal comfort. The BEPM is divided into two main modules: the adaptive comfort temperature (ACT) module and the new demand control ventilation (nDCV) module. This study aims to enhance and prompt the conventional operation of the air side systems by incorporating temperature reset with the adaptive comfort temperature control and the new demand control ventilation system in high rise buildings in Hong Kong. A new example weather year (1991) was established as a reference to compute the energy use of HVAC systems in buildings in order to obtain more representative data for predicting annual energy consumption. A survey of 165 Hong Kong office buildings was conducted and it provided valuable information on the existing HVAC design values in different grades of private commercial buildings in Hong Kong. It was found that the actual measured values of indoor temperature were lower than the design ones. Furthermore, with the new example weather year and the integration of the BEPM into Grade A private office buildings in Hong Kong, the total energy saving of the air conditioning systems was calculated (i.e. a saving of HK$122 million in electrical consumption per year) while the thermal comfort for the occupants was also maintained. (c) 2006 Elsevier Ltd. All rights reserved.