Computational fluid dynamics investigation of the thermal effectiveness of an oscillating air jet from a cassette split type air conditioner

A comfortable healthy indoor environment has become a major concern since people spend about 90% of their time in the indoor environment on average. Thermal uniformity in the indoor environment is not only about thermal comfort with high indoor environment quality, but it is also advantageous to assess diffusive performance of the air conditioner. The purpose of this study is to qualitatively investigate the thermal effectiveness of an oscillating air jet generated by side-to-side swing-type louvers (air delivery device) which are mounted inside a cassette split type air conditioner to provide the thermal uniformity. The impact of air supply control strategies such as louvers’ movement type, time interval, and swing angle, on indoor thermal environment were evaluated by Computation Fluid Dynamic (CFD) numerical simulation. A full-scale field experiment for validation is conducted in the environment chamber. The simulated result matches the experimental data well and verifies the feasibility of the proposed control method. In this study, the temperature performance was evaluated by: (i) average temperature difference and standard deviation (RMS) at represent sections; (ii) temperature utilisation coefficient for energy efficiency; (iii) air draught rate (DR%) on the face to determine the local discomfort due to cold draught in heating mode. The oscillating airflow as generated by the side-to-side swing deliver louvers mounted inside a cassette split type air conditioner could shorten warming time in heating conditions. In addition, the high temperature area is sign of the circle generates from diffusive type oscillating (louvers swing angle±40º) airflow. The supply air provides even temperature at each representative section compared to the conventional straight type airflow. The operation optimisation on the louvers’ movement parameters significantly improves the thermal uniformity, with a temperature difference reduction of 34% and draught rates on the face ranged 0-35% at 1.2m height horizontal section. The temperature utilisation coefficient varied in accordance with the louver’s directions, however, relatively poor temperature utilisation coefficients are occurred at the corners under straight type airflow.