Heat gains in commercial buildings in China are rather large compared to those of other public buildings, for occupant densities are usually high in such buildings. To match the requirements for both indoor environment and building energy conservation, ventilation systems, either mechanical ventilation, i.e., ventilating cooling (VC) or air-conditioning cooling (AC) systems, play important roles in maintaining good indoor air quality and thermal comfort. As the time durations for cooling and heating of AC systems in such buildings are different from other types of public buildings, temperature ranges for the application of different ventilation strategies all year round were obtained by using the local meteorological records in the present study. The results show that the time period in a whole year can be divided into five ranges according to the four outdoor critical temperatures for the operation of VC and AC systems with a heat recovery ventilator (HRV). The critical temperatures are mainly influenced by local climatic characteristics, occupant density, and pressure drop of the ventilation system, etc. Furthermore, energy effectiveness by employing different ventilation modes in commercial buildings with large internal gains was discussed and compared for four cities located in four different climatic zones of China. (C) 2012 Elsevier B.V. All rights reserved.