Comparison of underfloor and overhead air distribution systems in an office environment

This study compares thermal environment of two air distribution systems in an office setting. Airflow, heat and mass (water vapor and contaminant gas) transfer in steady-state condition are modeled for an underfloor air distribution system and an overhead air distribution system. The models include a typical cubicle in a large office floor with a chair, a desk with a personal computer on top, and heat sources such as seated person, desktop computer, and lights. For underfloor air distribution system, cool air enters the occupied zone through an inlet located at the floor level supplying a vertical upward inflow. Three different locations of the inlet diffuser are considered. For overhead air distribution, the inlet is located on the ceiling with slower and cooler inflow. Three inlet angles are considered. For both systems, the air return location is on the ceiling at the same place. Distributions of velocity, temperature, relative humidity, and contaminant concentration in various cases for both systems are computed. Thermal comfort factors are assessed for the two systems. The results are compared among cases of each system, as well as between two typical cases of the two systems and to experimental data for an actual office building given in literature. The results provide a detailed understanding of air transport and its consequence on thermal comfort and indoor air quality that are useful for office building air conditioner design. It is found that underfloor system gives better performance than overhead system in contaminant removal and significantly in energy saving while maintaining the same thermal comfort condition.