Cooling Performance of Air-Conditioning System with Ceiling Suspended Packaged Air Conditioning Unit over Divided-Type Membrane Ceilings in Large Classroom

The mainstream of air-conditioning system for medium and small sized buildings is conditionally air mixing ventilation with ceiling cassette unit of packaged air conditioner (PAC), however, it may bring a high cold-draught risk to occupants, due to the direct drop of the supply air jet. To solve this problem, the air mixing ventilation system can be improved into an air based radiant air-conditioning system by stretching the non-flammable membrane under the ceiling with PAC, thus the cold-draught of PAC could be substantially eliminated and the indoor environment could be improved easily. This air-conditioning system is named Membrane Ceiling Air-Conditioning System Using Ceiling Suspended PAC in this study. Many advantages of the system are (1) draught-less environment by inhibiting air velocity in occupation zone; (2) combination of the convective cooling by supplying micro airflow through a membrane ceiling and the radiative cooling from the cooled membrane ceiling; (3) the occupants' safety in case of the ceiling is collapsing because of its lightweight compared with the conventional ceiling materials; (4) the effect to avoid glare by diffusing illumination light. In addition, by dividing the membrane and making slits between them, that is divided-type, the convective airflow between the spaces across the membrane can be increased.  
However, it isn’t clear how the indoor environment will be affected by divided-type membrane ceiling air-conditioning system under various conditions. The aim of this study is to investigate the performance of this membrane ceiling air-conditioning system, and to conduct a Computational Fluid Dynamics (CFD) analysis on the airflows in the lecture room with this improved membrane ceiling air-conditioning system. The parameter in the CFD analysis is the membrane laying ratio, which is the ratio of membrane ceiling area to floor area. Furthermore, room air temperature, air flow pattern and two evaluation indices (DR and ADPI), and exchange air velocity were evaluated by CFD analysis. 
The result of this study shows that the improved membrane ceiling air-conditioning system can largely reduce the air velocity and thermal discomfort in occupied zone, compared with the traditional PAC. In addition, it is also shown that the membrane laying ratio would give a large effect on the indoor thermal environment, cooling efficiency and indoor air quality in the occupied zone.