Abstract: Buildings account for about 40% of total energy consumption worldwide. This consumed energy is usually as a result of the HVAC systems installed in the building which are delegated with the task of providing thermal comfort or a high quality indoor environment as humans spend about 90% of their time in buildings. With energy sources depleting at an unsustainable rate and contributing significantly to climate change, calls are intensifying for greener and more resource efficient systems.To support the drive towards a sustainable society, 4-way cassette air-conditioners are commonly deployed in offices in Eastern China. However, without optimal control of these systems, potential energy saving is lost while high level of indoor comfort is also not achieved.  The work in this paper presents a numerical investigation of thermal comfort in an office room with 4-way cassette air-conditioner. In this study, parameters such as supply air temperature and air velocity were varied to observe their effects on the comfort level in the room.The results show that the ability to control these parameters provides promising benefits for use to optimise the control of similar HVAC systems, resulting in building energy efficiency and improved occupant comfort or indoor environment quality.