The energy consumption of a building is significantly influenced by occupant behaviour. This paper presents an agent-based model that accounts for social interactions among occupants and quantitatively portrays the evolution process of their energy use patterns due to social norms. Several important factors influencing occupants' total energy consumption have been identified and examined within the model, including individual's energy use intensity (EUI) distribution and the introduction of energy-saving ambassadors into a scale-free social network. Results indicate that up to 40% of energy savings can be achieved through specific strategies, providing valuable insights for promoting sustainable practices among occupants in real world.