Study on the Thermal Comfort in Office Buildings Adopting Low-Velocity Air Circulation and Displacement Ventilation Systems

Abstract With the improvement of living standards, the demand for indoor comfort has increased. Fan coil systems have been found to cause uneven indoor temperature distribution, strong drafts, airflow short-circuiting, stagnant zones, and high noise levels during long-term use, thereby failing to ensure thermal comfort for occupants. This study investigates airflow characteristics and thermal comfort under low-velocity indoor air circulation. By adjusting fan coil and dehumidified displacement ventilation parameters, a more comfortable and healthier environment is achieved. The research focuses on a typical office fan coil unit with fresh air system. Environmental parameters were measured and recorded on an experimental platform in summer and winter to analyze the impact of different fan coil air parameters on indoor airflow and thermal comfort. The study shows that under low-velocity air circulation, short air jets cause temperature differences in the working area. However, the building envelope's insulation, airflow kinetics, and temperature field diffusion maintain stable indoor airflow and acceptable temperature uniformity. Compared to traditional systems, low-velocity systems reduce maximum air velocity by 62% in winter and 20% in summer, with a draft dissatisfaction coefficient of only 28–61%. For long-term seated occupants, optimal temperature settings and well-insulated envelopes are required.